Accepted Manuscript Hop performance and leg muscle power in athletes: Reliability of a test battery Kockum Britta, MSc Heijne I-L, M. Annette, PhD, RPT, University lecturer PII:
S1466-853X(14)00075-3
DOI:
10.1016/j.ptsp.2014.09.002
Reference:
YPTSP 629
To appear in:
Physical Therapy in Sport
Received Date: 16 December 2013 Revised Date:
25 August 2014
Accepted Date: 7 September 2014
Please cite this article as: Britta, K., Annette, H.I.-L,.M, Hop performance and leg muscle power in athletes: Reliability of a test battery, Physical Therapy in Sport (2014), doi: 10.1016/j.ptsp.2014.09.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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HOP PERFORMANCE AND LEG MUSCLE POWER IN ATHLETES:
AUTHORS: Kockum Britta1 MSc, Heijne I-L, M, Annette2 PhD 1
Swedish Sports Confederation Center, Bosön Sports Clinic, 181 47 Lidingö, Sweden, email:
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[email protected] 2
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RELIABILITY OF A TEST BATTERY
Karolinska Institutet, Department of Neurobiology, Care Sciences and Society (NVS),
CORRESPONDING AUTHOR:
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Division of Physiotherapy, 141 83 Huddinge, Sweden, email: [email protected]
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Annette Heijne, PhD, RPT, University lecturer Department of Neurobiology, Care Sciences and Society Karolinska Institutet 23 100 SE-141 83 HUDDINGE SWEDEN Phone: +46 (0)8 524 888 37 Mobile: +46 (0)70 509 48 33
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Fax: +46 (0)8 524 888 13
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[email protected]
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HOP PERFORMANCE AND LEG MUSCLE POWER IN ATHLETES:
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RELIABILITY OF A TEST BATTERY
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ABSTRACT
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Objectives: To measure the absolute and relative reliability and the smallest real difference
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(SRD) in three commonly used hop tests, two leg-power tests and the single-leg squat jump.
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Design: Methodological study
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Setting: Clinical setting
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Participants: Fourteen healthy athletes (seven women and seven men) were evaluated in a
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standardized test-retest design.
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Main outcome measures: The Intra-class correlation coefficient (ICC2.1), Standard Error of
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Measurement (SEM) and SRD were calculated for the vertical jump, one-leg hop for distance,
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side-hop, single-leg squat jump and knee-flexion and knee-extension power tests.
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Results: All tests showed good to excellent ICC (0.84–0.98). The SEM (%) ranged between
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3.4 and 11.1 for the four hop tests and between 8.1 and 12.4 for the leg-power tests. The SRD
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(%) for the hop tests ranged between 9.3 and 30.7 and for the three power tests between 22.4
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and 34.3.
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Conclusions: The absolute reliability of this test protocol showed good to excellent ICC
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values and measurement errors of approximately 10%. This instrument can be recommended
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for determining function in terms of power in healthy athletes or late in the rehabilitation
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process. The tests’ methodological errors must be considered and caution should be taken
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regarding the standardization procedure during testing.
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Key Words: hop tests, lower extremity function, outcome measures, single-leg squat jump
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INTRODUCTION
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Injuries to the lower extremities are common in sports. The reported incidence of re-injury is
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high for athletes returning to competitive sports at top levels (Salmon, Russell, Musgrove,
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Pinczewski, & Refshauge, 2005; Shelbourne, Gray, & Haro, 2009) and may be the result of
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insufficient rehabilitation (Hägglund, Ekstrand, & Waldén, 2006), asymmetrical movement
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patterns (Östenberg, Roos, Ekdahl, & Roos, 1998) or inadequate, in terms of reliability and
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validity, non-discriminative outcome measures regarding return to sports (Myer, Paterno,
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Ford, Carmen, & Hewett, 2006; Myklebust & Bahr, 2005; Paterno et al., 2010). Most sport-
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specific clinical measurements are sufficiently reliable when discriminating between injured
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and uninjured patients. However, in terms of sub-elite and elite athletes, methods need to be
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sensitive enough to discern finer differences (Atkinson & Nevill, 1998) and to determine an
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athlete’s readiness for higher level of performance.
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The gold standard for muscle strength evaluation is the isokinetic muscle torque test (Farrell,
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& Richards, 1986). However, this test has been questioned because there is a low correlation
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between isokinetic muscle torque and functional performance (Östenberg, Roos, Ekdahl &
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Roos, 1998). Instead, it has been suggested to use dynamic muscle power tests to evaluate
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muscle function (Augustsson &Thomée, 2000), given that the ability to produce high forces
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during high velocities is one of the most important factors in sports performance (Kraemer et
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al., 2002). A test battery for evaluation of leg muscle power after anterior cruciate ligament
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(ACL) injury, including both closed and opened kinetic chain exercises have earlier been
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developed (Neeter, Gustavsson, Thomée, Augustsson, Thomée, & Karlsson, 2006).
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In addition to power tests, hop tests have been highly recommended for evaluating sport-
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specific performance in healthy athletes and after various interventions (Hewitt, Stroupe,
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Nance, & Noyes, 1995; Paterno et al., 2010), particularly for sports involving twisting and
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cutting movements (Itoh, Kurosaka, & Yoshiya, 1998). . Further, functional knee stability,
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unilateral strength symmetry, power, endurance and agility are some of the criteria that should
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be evaluated to be able to determine readiness to safely return to sport following injury (Myer
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et al., 2011). A battery of hop tests, aiming to evaluate hop performance has earlier been
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described and analyzed for reliability, by Gustavsson et al. (2006). Three tests, with high
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capacity to discriminate hop performance, were chosen for inclusion in their test battery: the
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vertical jump, the hop for distance, and the side hop.
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The squat jump is one of the most frequently used exercises in the field of strength and
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conditioning (Chandler & Stone, 1991). It has biomechanical and neuromuscular similarities
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to a wide range of athletic movements (Escamilla, 2001) and is designed to enhance athletic
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performance, therefore regarded as a supreme test of lower-body strength (Schoenfeld, 2010).
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A resisted single-limb squat exercise involves simultaneous activation of the quadriceps and
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hamstring muscles that may increase the dynamic control of the knee (Shields, Gregg, Leitch,
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Petersen, Salata, & Wallerich, 2005). Such co-activation has frequently been suggested as one
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factor among several that play a major role in preventing injury of the knee (More, Karras,
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Neiman, Fritchy, Woo, & Daniel, 1993). Unilateral deficits may not be evident during
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bilateral movements (Myer et al., 2011); therefore a dynamic single-limb test is advocated to
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show deficits in function owing to an injury to the lower extremity.
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The reliability of a squat-jump test on a single leg with external loading has not yet been
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established in the literature. The aim of this study was to measure the absolute and relative
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reliability and the smallest real difference (SRD) in three commonly used hop tests, two leg-
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power tests on a device and the single-leg squat jump, with external weight.
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METHODS
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Subjects
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Eighteen healthy athletes (nine women and nine men), average age 23.4 years (SD:2.4),
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average weight 72.1 kg (SD:15.3) and average height 172 cm (SD:11.0) were asked to
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participate in this study.
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All athletes were active in sports at both recreational and competitive levels. The inclusion
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criterion was that athletes had been able to fully participate in their sport or to be physically
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active (6-8 sessions/week) three months prior to the test session with no pain and no reduced
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function. Two women and two men could not complete the study due to nerve entrapment
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(n=1), illness (n=1), or injury (n=2). Fourteen healthy athletes were therefore evaluated in a
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standardized test-retest design, with 7–10 days between tests. The group of athletes had
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various levels of experience with barbell squat exercises and weight training, according to
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their own accounts. When asked, four considered themselves experts, four were novices, and
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10 were familiar with general weight training and barbell squat exercises.
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The present study was approved by a local committee consisting of senior researchers at
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Karolinska Institutet, Stockholm, Sweden. Ethical considerations in the study have followed
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the recommendations Harris and Atkinson (2011).
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Procedure
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The subjects were all students from the same school of sports. The exercises were tested in
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the same at the two test occasions. The training load or training manners regarding the
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physical practice in school was persistent over the 7-10 days according to the subjects. The
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amount of individual training could be different from subject to subject – depending on what
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activity level they were in sports. The participants were told to do the regular amount of
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training and competition and intensive heavy strength or jumping was not allowed 48 hrs
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before the testing. The testing was performed in the same laboratory which had the same
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temperature and humidity at the time of testing. The tests were performed at day-time but
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could differ from morning to afternoon. All tests were supervised by the same test leader and
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similar verbal encouragement was used in all case.
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The test battery; vertical jump, one-leg hop for distance, side hop, single-leg squat jump,
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knee-flexion and knee-extension power tests were described to the athletes consecutively.
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Before the tests, a standardized warm-up program was performed comprising 10 minutes on a
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stationary bike, two sets of 15 repetitions of toe raises and two sets of 6 repetitions of tuck
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jumps. Immediately prior to the vertical jump and the hop for distance, each athlete was
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allowed to practice three to five trials on each leg, followed by a one-minute rest; and before
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the side-hop test, the subject was allowed to practice 10–15 jumps to become acquainted with
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the hop test. The single-leg squat-jump test required initial positioning of the knee at a 90°
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angle; thus subjects became warmed up and acquainted with the test, as they needed to squat
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bilaterally three to four times in order to find the appropriate starting position. Prior to the
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hamstring and quadriceps muscle-power tests, each athlete was allowed to perform 10
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bilateral familiarization sessions on sub-maximum weights, followed by a two-minute rest.
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Technical equipment
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An Ivar jump mat® (IVAR measuring systems, Tallin, Estland) was used for evaluation of the
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vertical jump. This jump mat is constructed with a field of infrared light beams that are
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triggered when a subject jumps off the mat and thus interrupts the beams. The system records
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the ground-contact time and air-flight times.
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Mechanical power output in a given task was obtained from the direct or indirect
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measurements of parameters such as time, displacement and force using inverse dynamics
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approach (Hori et al., 2007). The Muscle Lab® (Ergotest Technology, Oslo, Norway) linear
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position transducer measurement system was used for evaluation of power. The Muscle Lab®
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system consists of a spring-loaded string that is connected to a sensor inside the linear
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encoder unit. When the string is pulled, the sensor outputs a series of digital pulses
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proportional to the distance traveled. The resolution is approximately one pulse every 0.07
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mm. By counting the number of pulses per time segment, the system records the displacement
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as a function of time can be recorded and thus allow calculation of velocity. Further, knowing
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the body mass and external load (f = m*a), power was then calculated as force times velocity.
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In the present study the string was attached to the specific weight used in the various power
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tests.
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Hop tests
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Vertical jump
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The vertical jump test was performed as a countermovement jump (CMJ) (Komi & Bosco,
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1978). The starting position was standing on one leg in an upright position with hands on the
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hips. The athlete quickly flexed the knee as much as desired and then immediately jumped
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upwards, attempting to maximize the jump height. The subject was requested to land on a
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straight knee, followed by a rebound jump. Hands were to be kept on the hips throughout the
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test. Three maximal approved trials were recorded for each leg, starting with the right leg and
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alternating legs for every jump. Additional jumps were allowed if increased jump height was
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demonstrated. The jump height in centimeters was recorded.
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One-leg hop for distance
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The subject began the hop for distance standing on one leg, toes behind a mark on the floor.
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Keeping the hands on the hips throughout the jump, the athlete jumped forward as far as
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possible. The subject was instructed to perform a controlled landing (Neeter et al., 2006). The
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test was performed until three successful jumps were performed for each leg, starting with the
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right leg and thereafter alternating right and left leg. The distance in centimeters was
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measured.
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Side-hop
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Standing on one leg with hands on hips, the athletes were asked to jump from side to side
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between two parallel lines 40 cm apart as many times as possible in 30 seconds. If the foot
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landed on the line or if the other foot touched the floor, the jump was considered incorrect.
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Subjects’ hands were to be kept on their hips throughout the test (Itoh et al., 1998; Gustavsson
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et al., 2006). The number of correct jumps was recorded for each athlete.
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Strength tests
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Single-leg squat jump
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A concentric squat-jump test on one leg was performed in a modified Smith machine (Nordic
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Gym, Bollnäs, Sweden); the barbell weighed 21.4 kg, and the power rack was elongated to
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allow for a jumping motion. Hands were placed an even distance between each other more
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than shoulder width apart. The athlete was instructed to keep the body in an upright position
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during the whole test. To define the starting position of a 90°, the subject performed three to
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four bilateral squats with the feet shoulder width apart, slightly externally rotated, and placed
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on a marked line on the floor that corresponded to a line through the transverse line of the
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malleoli (Figure 1a). With a standard goniometer, the correct angle of 90° knee flexion was
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measured and a moveable stopper was placed on the safety rack, defining an individual
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starting position. The subject was instructed to stand on one leg with the foot centered under
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the barbell (Figure 1b). The foot was placed such that the center of mass was immediately
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under the foot on the same transverse line as in the bilateral starting position, and also on a
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straight sagittal line in accordance with the metacarpal II, indicated by the line of a laser
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beam. Two warm-up squat jumps from the starting position of 90° were performed on each
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leg using the load of the bar. On a given signal the test started and the subject was told to
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perform a maximum squat from 90° of flexion as quickly as possible and with maximum
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effort to ascend to full knee and hip extension, followed by a smooth landing. In total, the
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subject performed 10 maximal trials, two trials on five weight levels with a two-minute rest
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period between trials. The first load was 21.4 kg and thereafter 50%, 60%, 70%, and 80%
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BW. A linear position transducer was attached to the bar and measured the vertical
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displacement of the bar with an accuracy of 0.01 cm. The maximum average power was
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calculated by the Muscle Lab.
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Knee-flexion power test
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The knee-flexion power test (Neeter et al., 2006) was performed on a seated leg-flexion
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weight-training machine (Seated Leg Curl 103 SE, Nordic Gym, Bollnäs, Sweden). The
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footpad was placed approximately 5 cm above the lateral malleoli, and the back seat was
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positioned so that the knee joint aligned with the axis of the resistance arm of the machine.
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The test was unilaterally performed starting with the left leg and alternating with the right leg.
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The warm-up consisted of 10 submaximal (70% of 1 RM) bilateral leg curl repetitions. The
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first external testing load was half the warm-up weight. The test was performed with two
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trials on each leg with maximum effort and on five weight levels. The weight was increased
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by 2.5 kg to 5 kg with two minutes of rest between trials. The five loads assessed were
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between 40% and 70% of the individual’s 1 RM. On a given signal, the subject was asked to
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flex his or her knee as quickly and as forcefully as possible from full knee extension to
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approximately 110º knee flexion. The distance the weight stack was lifted and the time it took
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to fully flex the knee were measured with a linear encoder connected to the machine’s weight
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stack. After the five trials the maximum average power was calculated by the Muscle Lab.
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Knee-extension power test
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The knee-extension power test (Neeter et al., 2006) was performed on a knee-extension
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weight-training machine (Leg Extension 101 SE, Nordic Gym, Bollnäs, Sweden). The same
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procedure as that for the knee-flexion power test was used. The test was performed from
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approximately 110º knee flexion to full knee extension.
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Statistical Analyses
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No power calculation was performed prior to this study, instead the number of subjects was
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estimated based on that the number of individuals * the number of tests shouldn’t be less than
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25 (Bruton et al., 2000). For data on participants’ characteristics, mean and standard deviation
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(SD) were calculated. A paired-sample t-test was used to assess systematic changes between
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the two tests. To check for systematic bias, outliers, and heteroscedasticity, the data were
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visualized in Bland and Altman plots (Bland & Altman, 1986). Relative reliability; the
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intraclass correlation coefficient, was assessed by ICC2.1 (Atkinson & Nevill, 1998; Lexell &
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Downham, 2005). Absolute reliability was calculated with the standard error of measurement
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(SEM), SEM%, a measure of repeatability and repeatability percentage. SEM was defined as
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the within-subject standard deviation, that is the square root of the within-subject variance
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(WMS)
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Downham, 2005). The SEM and SEM% can be used to determine the limit for the smallest
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real difference (SRD). To determine the SRD, a measure of repeatability (Lexell & Downham,
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2005) and repeatability as a percentage of the mean were calculated according to these
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formulas: Repeatability =
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, and further,
(Atkinson & Nevill, 1998; Lexell &
and Repeatability % =
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significant level of p < 0.05 was used. The 95% limits of agreement for all the test variables
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were calculated as the inter trial mean difference ± 1.96 SD. All calculations were performed
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using SPSS for Windows (release 20.0).
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RESULTS
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Absolute values for the tests are shown in Table 1. No significant differences were found in
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any of the tests when comparing the absolute values of tests 1 and 2, except for the side-hop
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test, left leg (P = 0.01).
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Table 1 (about here)
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Good to excellent test-retest reliability (ICC2.1:0.84-0.98) was found in all tests for the left and
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right legs. Absolute values in SEM for the six tests are shown in Table 2. The SEM (%)
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ranged between 3.4 and 11.1 for the hop tests and between 8.1 and 12.4 for the power tests
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(Table 2). The smallest real differences (SRD) for the hop tests ranged between 9.3% and
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30.7% and between 24.1% and 34.3% for the three power tests (Table 2). Bland and Altman
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plots for all tests can be found as supplementary electronic data.
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Table 2 (about here)
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DISCUSSION
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To our knowledge this is the first study to examine the absolute reliability and, further, the
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SRD for the knee-flexion, knee-extension, and single-leg squat-jump tests in terms of power.
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The absolute agreement calculated with the ICC2.1 model was high, 0.88-0.96 (Vincent,
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1994). Further, the ICC for the vertical jump, the hop for distance, and the side-hop tests
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ranged from good to high absolute agreement, 0.84-0.98. In addition, the 95% CI for all
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included tests, right and left leg, was narrow, indicating good agreement.
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The ICC includes the variance term for individuals and is therefore affected by sample size
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heterogeneity, meaning that a high correlation can still mean unacceptable measurement error
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(Atkinson & Nevill, 1998). In the present study we therefore further analyzed the absolute
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agreement, which is unaffected by the range of measurements. One indicator of absolute
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reliability or the measurement variability is the SEM (Lexell & Downham, 2005). The smaller
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the SEM, the more reliable the measurement, which is often used to interpret the results of an
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improvement after an intervention. The reported SEM% for the six tests in the present study
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ranged from 3.4% to 12.4%, demonstrating that an improvement that is smaller does not
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indicate a clinically important improvement. The SEM data in the present study regarding the
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vertical jump, the hop for distance, and the side hop align closely with previously reported
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data (Neeter et al., 2006). For the knee-extension and the knee-flexion tests, our data reveal
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somewhat higher methodological error compared to those reported by Neeter et al. (2006) and
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for the newly developed more complex exercise, the single-leg squat jump, the average
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SEM% for left and right leg was 9.1%, representing approximately 75 Watt. However, it is
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important to take into consideration that several statistical assumptions are involved when
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calculating the SEM (Atkinsson & Nevill, 1998). In the literature there is no clarity regarding
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an acceptable SEM; instead, one must consider in what context the measurement is used and
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what is clinically acceptable.
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The smallest real difference (SRD) or repeatability is one way to statistically describe or
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express a measurement’s clinometric property, not to be confused with clinically important
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changes (Bland and Altman, 1986; Lexell & Downham, 1995; Turner et al., 2012). Minimal
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clinically important changes (MIC) should rather be chosen arbitrarily, referred to what
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clinicians, scientist, and patients’ rate as an important change or one that affects an individual
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functional performance (Lexell & Downham, 2005; Turner et al., 2012). According to
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analysis in the present study, it is important to determine the 95% CI in order to present a
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useful reference range. If no arbitrarily chosen MIC is available for the method of interest, it
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is recommended that SEM be used to approximate a small change (Turner et al., 2012)
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between two different measures, such as before and after an intervention period.
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To isolate and detect strength deficiency of the hamstrings- or the quadriceps musculature is
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of great importance after knee rehabilitation since a history of previous injury has been
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associated with sustaining a new injury (Alonso et al., 2012). Further, it has been found that
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biomechanical measures during landing and postural stability can predict second anterior
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cruciate ligament injury after anterior cruciate ligament reconstruction and return to play
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(Paterno et al., 2010). The importance of testing single-leg squat motions as well as single-leg
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hops, and landing function has lately been advocated by many authors (Myer et al., 2006;
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Tagesson & Kvist, 2007; von Porat, Holmström, & Roos, 2008). Gustavsson et al. (2012)
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found abnormal symmetry in five different one-legged hop tests ranging from 43 to 77% for
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patients with an ACL injury (11 months post injury) and from 51 to 86% for patients who had
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undergone ACL reconstruction (6 months post operatively), respectively. The squat jump on
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two legs is commonly used for training and testing power among athletes, especially in sports
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involving acceleration movements such as sprinting, jumping, and throwing (Escamilla, 2001;
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Peterson et al., 2006), however, the single-leg squat simulates to a higher extend, a common
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athletic position requiring control of the body over the single fixed lower leg (Schoenfeld,
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2010; Trulsson, Garwicz, & Agerberg, 2010; Zätterström, Fridén, Lindstrand, & Moritz,
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2000). Neeter et al. (2006) studied a single-legged squat with the subjects in a supine position
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(leg press), and is therefore probably less sport-specific, since squatting in a standing position
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puts higher demands on trunk stability and coordination. One might therefore expect to see
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lower ICC values in standing position compared to lying down. Our study confirms this
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hypothesis, showing somewhat lower ICC, 0.88-0.93, compared to that found by Neeter et al.
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(2006), 0.94-0.98.
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The low number of included subject in the present study can be considered as a limitation,
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however a commonly described advise in the literature is that the number of individuals * the
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number of tests, shouldn’t be less than 25 (Bruton et al 2000; Chinn 1991), in our study 28.
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No power calculation was performed prior to the study, instead we were concerned with the
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degree of agreement, so that this problem is one of estimation rather than hypothesis testing,
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meaning we do not expect any differences between test one and test two.
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CONCLUSIONS
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The absolute reliability of this test protocol was clinically acceptable when testing healthy
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athletes, with good to excellent ICC values and measurement errors of approximately 10%.
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The test battery reflects athletic performance involving jumping movements with and without
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external loading (a single-leg squat) and leg power. The feasibility of the instrument for
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injured athletes is not known, but this test battery can be recommended for determining
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whether an athlete is ready to return to sport after an injury, since several of the involved tests
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are highly sport specific. The most sport-specific test, the single-leg squat jump, is also
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recommended as a preseason test for athletes involved in sports that require power and
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jumping qualities.
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CONFLICTS OF INTEREST AND SOURCE OF FUNDING We have no conflicts of interest and no external funding has been received for this study.
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31. Turner, D., Schünemann, H.J., Griffith, L.E., Beaton, D.E, Griffiths, A.M., Critch, J.N., and Guyatt, G.H. (2012). The minimal detectable change cannot reliably replace
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32. Vincent J. Statistics in kinesiology. Champaign (IL): Human Kinetics Books, 1994.
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videotaped functional performance tests in ACL-injured subjects. Physiother Res Int, 13(2), 119-130.
34. Zätterström, R., Friden, T., Lindstrand, A., and Moritz, U. (2000). Rehabilitation
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35. Östenberg, A., Roos, E., Ekdahl, C., and Roos, H. (1998). Isokinetic knee extensor
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strength and functional performance in healthy female soccer players. Scand J Med Sci
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Sports, 8, 257-264.
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ACKNOWLEDGMENTS We would like to acknowledge all the study participants and thank them for sharing their time
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with us.
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Tables Table 1: Absolute values for the right (R) and left (L) leg (n=14) for the vertical jump, hop for distance, side hop, single-legged squat jump, knee flexion and knee extension tests. Mean and Standard Deviation (SD) is presented. Mean (SD) Test 2
Difference Test 1-Test 2 (SD) Vertical jump (cm), R 17.2 (5.3) 17.3 (5.4) 0.1 (0.9) Vertical jump (cm), L 17.1 (5.0) 17.3 (5.5) 0.2 (0.8) Hop for distance (cm), R 141.3 (29) 144.5 (25.9) 3.2 (6.6) Hop for distance (cm), L 143.1 (28.4) 146.5 (27.5) 3.4 (6.9) Side hop (no/30s), R 47.0 (12.8) 49.6 (13.5) 2.6 (7.4) Side hop (no/30s,) L 45.1 (12.6) 47.4 (13) 2.3 (2.9) Single-legged squat jump (Watt), R 810.2 (214.2) 848.9 (216.7) 38.7 (98.2) Single-legged squat jump (Watt), L 804.5 (212.3) 823.3 (233.4) 18.8 (111.4) Knee flexion (Watt), R 168.7 (64.1) 176.1 (58.9) 7.4 (19.0) Knee flexion (Watt), L 156.5 (54.4) 163.7 (49.3) 7.2 (19.6) Knee extension (Watt), R 212.7 (74.8) 220.1 (85.2) 7.4 (28.3) Knee extension (Watt), L 215.5 (95.8) 213.6 (74.8) - 1.9 (39.0)
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0.84 0.43 0.09 0.09 0.22 0.01** 0.16 0.54 0.17 0.19 0.34 0.86
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Table 2. Relative and Absolute reliability of the six included tests for left (L) and right (R) leg (n=14). (Intra Class Correlation (ICC), Standard Error of Measurement (SEM), Smallest Real Difference (SRD)). SEM (%)
SRD
SRD (%)
0.63 (cm) 0.58 (cm) 5.0 (cm) 5.3 (cm) 5.4 (no)
3.6
10.0
- 1,77
1,67
9.3
-1,77
1,42
9.7
-17,12
10,69
10.1
-17,92
11,21
2.5 (no) 72.3 (Watt)
5.5
1.72 (cm) 1.6 (cm) 13.9 (cm) 14.6 (cm) 14.8 (no) 7.0 (no)
8.7
200.2 (Watt)
0.97
0.9-0.99
0.97
0.89-0.99
0.84
0.58-0.94
0.96
0.79-0.99
0.91
0.74-0.97
0.88
0.67-0.96
77.0 (Watt)
9.5
0.95
0.85-0.98
8.1
0.96
0.78-0.98
13.9 (Watt) 14.3 (Watt) 20.0 (Watt) 26.6 (Watt)
0.94 0.91
0.82-0.98 0.72-0.97
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3.4 3.5 3.6
8.9 9.2
12.4
95 % SRD upper
30.7
-17,41
12,27
15.2
-9,31
4,74
24.1
-238,94
161,47
213.4 (Watt)
26.2
-232,20
194,59
38.6 (Watt) 39.6 (Watt) 55.4 (Watt) 73.7 (Watt)
22.4
-46,02
31,23
24.8
-46,85
32,44
25.6
-62,82
47,94
34.3
-71,79
75,57
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Vertical jump (cm), R Vertical jump (cm), L Hop for distance (cm), R Hop for distance (cm), L Side hop (no/30s), R Side hop (no/30s,) L Single-legged squat jump (Watt), R Single-legged squat jump (Watt), L Knee flexion (Watt), R Knee flexion (Watt), L Knee extension (Watt), R Knee extension (Watt), L
ICC2.1 95 % CI (lowerupper bound) 0.98 0.94-0.99
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Figure 1a and 1b. The single-leg squat jump, starting and flight position.
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HIGHLIGHTS FOR REVIEW Three hop tests, two leg-power tests and the single-leg squat jump were evaluated.
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The ICC of this test battery was good to excellent (0.84-0.98)
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The ICC for the newly developed single-leg squat jump was high (0.88-0.91).
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The measurement errors of approximately 10% is clinically acceptable
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This test battery can be used for determining power in healthy athletes. .
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Caution should be taken regarding the standardization procedure during testing.
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CONFLICTS OF INTEREST AND SOURCE OF FUNDING
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We have no conflicts of interest and no external funding has been received for this study.
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The present study was approved by a local committee consisting of senior researchers at Karolinska Institutet, Departments of Neurobiology, Care Sciences and Society, division fo physiotherapy. Ethical considerations in the study have followed the recommendations Harris
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and Atkinson (Harris & Atkinson, 2011).
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Difference in One-legged hop test (test 1-test 2) (cm)
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Difference Side hop test (test 1-test 2) (no of jumps)
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Average (no of jumps) test 1-test 2, Side hop test
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Difference in Single-legged squat jump (test 1-test 2) (Watt)
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Average (Watt) between test 1 and test 2, Single-legged squat jump
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Average (Watt) between test 1 and test 2, Leg-extension
S1466-853X(14)00075-3
DOI:
10.1016/j.ptsp.2014.09.002
Reference:
YPTSP 629
To appear in:
Physical Therapy in Sport
Received Date: 16 December 2013 Revised Date:
25 August 2014
Accepted Date: 7 September 2014
Please cite this article as: Britta, K., Annette, H.I.-L,.M, Hop performance and leg muscle power in athletes: Reliability of a test battery, Physical Therapy in Sport (2014), doi: 10.1016/j.ptsp.2014.09.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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HOP PERFORMANCE AND LEG MUSCLE POWER IN ATHLETES:
AUTHORS: Kockum Britta1 MSc, Heijne I-L, M, Annette2 PhD 1
Swedish Sports Confederation Center, Bosön Sports Clinic, 181 47 Lidingö, Sweden, email:
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[email protected] 2
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RELIABILITY OF A TEST BATTERY
Karolinska Institutet, Department of Neurobiology, Care Sciences and Society (NVS),
CORRESPONDING AUTHOR:
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Division of Physiotherapy, 141 83 Huddinge, Sweden, email: [email protected]
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Annette Heijne, PhD, RPT, University lecturer Department of Neurobiology, Care Sciences and Society Karolinska Institutet 23 100 SE-141 83 HUDDINGE SWEDEN Phone: +46 (0)8 524 888 37 Mobile: +46 (0)70 509 48 33
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Fax: +46 (0)8 524 888 13
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[email protected]
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HOP PERFORMANCE AND LEG MUSCLE POWER IN ATHLETES:
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RELIABILITY OF A TEST BATTERY
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ABSTRACT
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Objectives: To measure the absolute and relative reliability and the smallest real difference
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(SRD) in three commonly used hop tests, two leg-power tests and the single-leg squat jump.
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Design: Methodological study
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Setting: Clinical setting
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Participants: Fourteen healthy athletes (seven women and seven men) were evaluated in a
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standardized test-retest design.
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Main outcome measures: The Intra-class correlation coefficient (ICC2.1), Standard Error of
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Measurement (SEM) and SRD were calculated for the vertical jump, one-leg hop for distance,
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side-hop, single-leg squat jump and knee-flexion and knee-extension power tests.
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Results: All tests showed good to excellent ICC (0.84–0.98). The SEM (%) ranged between
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3.4 and 11.1 for the four hop tests and between 8.1 and 12.4 for the leg-power tests. The SRD
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(%) for the hop tests ranged between 9.3 and 30.7 and for the three power tests between 22.4
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and 34.3.
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Conclusions: The absolute reliability of this test protocol showed good to excellent ICC
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values and measurement errors of approximately 10%. This instrument can be recommended
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for determining function in terms of power in healthy athletes or late in the rehabilitation
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process. The tests’ methodological errors must be considered and caution should be taken
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regarding the standardization procedure during testing.
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Key Words: hop tests, lower extremity function, outcome measures, single-leg squat jump
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INTRODUCTION
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Injuries to the lower extremities are common in sports. The reported incidence of re-injury is
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high for athletes returning to competitive sports at top levels (Salmon, Russell, Musgrove,
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Pinczewski, & Refshauge, 2005; Shelbourne, Gray, & Haro, 2009) and may be the result of
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insufficient rehabilitation (Hägglund, Ekstrand, & Waldén, 2006), asymmetrical movement
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patterns (Östenberg, Roos, Ekdahl, & Roos, 1998) or inadequate, in terms of reliability and
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validity, non-discriminative outcome measures regarding return to sports (Myer, Paterno,
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Ford, Carmen, & Hewett, 2006; Myklebust & Bahr, 2005; Paterno et al., 2010). Most sport-
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specific clinical measurements are sufficiently reliable when discriminating between injured
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and uninjured patients. However, in terms of sub-elite and elite athletes, methods need to be
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sensitive enough to discern finer differences (Atkinson & Nevill, 1998) and to determine an
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athlete’s readiness for higher level of performance.
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The gold standard for muscle strength evaluation is the isokinetic muscle torque test (Farrell,
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& Richards, 1986). However, this test has been questioned because there is a low correlation
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between isokinetic muscle torque and functional performance (Östenberg, Roos, Ekdahl &
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Roos, 1998). Instead, it has been suggested to use dynamic muscle power tests to evaluate
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muscle function (Augustsson &Thomée, 2000), given that the ability to produce high forces
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during high velocities is one of the most important factors in sports performance (Kraemer et
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al., 2002). A test battery for evaluation of leg muscle power after anterior cruciate ligament
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(ACL) injury, including both closed and opened kinetic chain exercises have earlier been
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developed (Neeter, Gustavsson, Thomée, Augustsson, Thomée, & Karlsson, 2006).
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In addition to power tests, hop tests have been highly recommended for evaluating sport-
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specific performance in healthy athletes and after various interventions (Hewitt, Stroupe,
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Nance, & Noyes, 1995; Paterno et al., 2010), particularly for sports involving twisting and
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cutting movements (Itoh, Kurosaka, & Yoshiya, 1998). . Further, functional knee stability,
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unilateral strength symmetry, power, endurance and agility are some of the criteria that should
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be evaluated to be able to determine readiness to safely return to sport following injury (Myer
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et al., 2011). A battery of hop tests, aiming to evaluate hop performance has earlier been
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described and analyzed for reliability, by Gustavsson et al. (2006). Three tests, with high
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capacity to discriminate hop performance, were chosen for inclusion in their test battery: the
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vertical jump, the hop for distance, and the side hop.
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The squat jump is one of the most frequently used exercises in the field of strength and
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conditioning (Chandler & Stone, 1991). It has biomechanical and neuromuscular similarities
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to a wide range of athletic movements (Escamilla, 2001) and is designed to enhance athletic
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performance, therefore regarded as a supreme test of lower-body strength (Schoenfeld, 2010).
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A resisted single-limb squat exercise involves simultaneous activation of the quadriceps and
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hamstring muscles that may increase the dynamic control of the knee (Shields, Gregg, Leitch,
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Petersen, Salata, & Wallerich, 2005). Such co-activation has frequently been suggested as one
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factor among several that play a major role in preventing injury of the knee (More, Karras,
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Neiman, Fritchy, Woo, & Daniel, 1993). Unilateral deficits may not be evident during
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bilateral movements (Myer et al., 2011); therefore a dynamic single-limb test is advocated to
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show deficits in function owing to an injury to the lower extremity.
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The reliability of a squat-jump test on a single leg with external loading has not yet been
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established in the literature. The aim of this study was to measure the absolute and relative
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reliability and the smallest real difference (SRD) in three commonly used hop tests, two leg-
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power tests on a device and the single-leg squat jump, with external weight.
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METHODS
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Subjects
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Eighteen healthy athletes (nine women and nine men), average age 23.4 years (SD:2.4),
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average weight 72.1 kg (SD:15.3) and average height 172 cm (SD:11.0) were asked to
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participate in this study.
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All athletes were active in sports at both recreational and competitive levels. The inclusion
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criterion was that athletes had been able to fully participate in their sport or to be physically
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active (6-8 sessions/week) three months prior to the test session with no pain and no reduced
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function. Two women and two men could not complete the study due to nerve entrapment
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(n=1), illness (n=1), or injury (n=2). Fourteen healthy athletes were therefore evaluated in a
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standardized test-retest design, with 7–10 days between tests. The group of athletes had
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various levels of experience with barbell squat exercises and weight training, according to
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their own accounts. When asked, four considered themselves experts, four were novices, and
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10 were familiar with general weight training and barbell squat exercises.
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The present study was approved by a local committee consisting of senior researchers at
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Karolinska Institutet, Stockholm, Sweden. Ethical considerations in the study have followed
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the recommendations Harris and Atkinson (2011).
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Procedure
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The subjects were all students from the same school of sports. The exercises were tested in
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the same at the two test occasions. The training load or training manners regarding the
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physical practice in school was persistent over the 7-10 days according to the subjects. The
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amount of individual training could be different from subject to subject – depending on what
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activity level they were in sports. The participants were told to do the regular amount of
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training and competition and intensive heavy strength or jumping was not allowed 48 hrs
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before the testing. The testing was performed in the same laboratory which had the same
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temperature and humidity at the time of testing. The tests were performed at day-time but
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could differ from morning to afternoon. All tests were supervised by the same test leader and
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similar verbal encouragement was used in all case.
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The test battery; vertical jump, one-leg hop for distance, side hop, single-leg squat jump,
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knee-flexion and knee-extension power tests were described to the athletes consecutively.
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Before the tests, a standardized warm-up program was performed comprising 10 minutes on a
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stationary bike, two sets of 15 repetitions of toe raises and two sets of 6 repetitions of tuck
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jumps. Immediately prior to the vertical jump and the hop for distance, each athlete was
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allowed to practice three to five trials on each leg, followed by a one-minute rest; and before
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the side-hop test, the subject was allowed to practice 10–15 jumps to become acquainted with
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the hop test. The single-leg squat-jump test required initial positioning of the knee at a 90°
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angle; thus subjects became warmed up and acquainted with the test, as they needed to squat
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bilaterally three to four times in order to find the appropriate starting position. Prior to the
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hamstring and quadriceps muscle-power tests, each athlete was allowed to perform 10
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bilateral familiarization sessions on sub-maximum weights, followed by a two-minute rest.
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Technical equipment
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An Ivar jump mat® (IVAR measuring systems, Tallin, Estland) was used for evaluation of the
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vertical jump. This jump mat is constructed with a field of infrared light beams that are
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triggered when a subject jumps off the mat and thus interrupts the beams. The system records
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the ground-contact time and air-flight times.
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Mechanical power output in a given task was obtained from the direct or indirect
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measurements of parameters such as time, displacement and force using inverse dynamics
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approach (Hori et al., 2007). The Muscle Lab® (Ergotest Technology, Oslo, Norway) linear
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position transducer measurement system was used for evaluation of power. The Muscle Lab®
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system consists of a spring-loaded string that is connected to a sensor inside the linear
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encoder unit. When the string is pulled, the sensor outputs a series of digital pulses
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proportional to the distance traveled. The resolution is approximately one pulse every 0.07
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mm. By counting the number of pulses per time segment, the system records the displacement
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as a function of time can be recorded and thus allow calculation of velocity. Further, knowing
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the body mass and external load (f = m*a), power was then calculated as force times velocity.
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In the present study the string was attached to the specific weight used in the various power
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tests.
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Hop tests
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Vertical jump
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The vertical jump test was performed as a countermovement jump (CMJ) (Komi & Bosco,
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1978). The starting position was standing on one leg in an upright position with hands on the
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hips. The athlete quickly flexed the knee as much as desired and then immediately jumped
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upwards, attempting to maximize the jump height. The subject was requested to land on a
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straight knee, followed by a rebound jump. Hands were to be kept on the hips throughout the
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test. Three maximal approved trials were recorded for each leg, starting with the right leg and
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alternating legs for every jump. Additional jumps were allowed if increased jump height was
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demonstrated. The jump height in centimeters was recorded.
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One-leg hop for distance
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The subject began the hop for distance standing on one leg, toes behind a mark on the floor.
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Keeping the hands on the hips throughout the jump, the athlete jumped forward as far as
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possible. The subject was instructed to perform a controlled landing (Neeter et al., 2006). The
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test was performed until three successful jumps were performed for each leg, starting with the
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right leg and thereafter alternating right and left leg. The distance in centimeters was
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measured.
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Side-hop
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Standing on one leg with hands on hips, the athletes were asked to jump from side to side
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between two parallel lines 40 cm apart as many times as possible in 30 seconds. If the foot
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landed on the line or if the other foot touched the floor, the jump was considered incorrect.
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Subjects’ hands were to be kept on their hips throughout the test (Itoh et al., 1998; Gustavsson
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et al., 2006). The number of correct jumps was recorded for each athlete.
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Strength tests
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Single-leg squat jump
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A concentric squat-jump test on one leg was performed in a modified Smith machine (Nordic
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Gym, Bollnäs, Sweden); the barbell weighed 21.4 kg, and the power rack was elongated to
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allow for a jumping motion. Hands were placed an even distance between each other more
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than shoulder width apart. The athlete was instructed to keep the body in an upright position
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during the whole test. To define the starting position of a 90°, the subject performed three to
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four bilateral squats with the feet shoulder width apart, slightly externally rotated, and placed
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on a marked line on the floor that corresponded to a line through the transverse line of the
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malleoli (Figure 1a). With a standard goniometer, the correct angle of 90° knee flexion was
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measured and a moveable stopper was placed on the safety rack, defining an individual
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starting position. The subject was instructed to stand on one leg with the foot centered under
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the barbell (Figure 1b). The foot was placed such that the center of mass was immediately
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under the foot on the same transverse line as in the bilateral starting position, and also on a
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straight sagittal line in accordance with the metacarpal II, indicated by the line of a laser
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beam. Two warm-up squat jumps from the starting position of 90° were performed on each
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leg using the load of the bar. On a given signal the test started and the subject was told to
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perform a maximum squat from 90° of flexion as quickly as possible and with maximum
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effort to ascend to full knee and hip extension, followed by a smooth landing. In total, the
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subject performed 10 maximal trials, two trials on five weight levels with a two-minute rest
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period between trials. The first load was 21.4 kg and thereafter 50%, 60%, 70%, and 80%
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BW. A linear position transducer was attached to the bar and measured the vertical
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displacement of the bar with an accuracy of 0.01 cm. The maximum average power was
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calculated by the Muscle Lab.
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Knee-flexion power test
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The knee-flexion power test (Neeter et al., 2006) was performed on a seated leg-flexion
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weight-training machine (Seated Leg Curl 103 SE, Nordic Gym, Bollnäs, Sweden). The
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footpad was placed approximately 5 cm above the lateral malleoli, and the back seat was
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positioned so that the knee joint aligned with the axis of the resistance arm of the machine.
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The test was unilaterally performed starting with the left leg and alternating with the right leg.
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The warm-up consisted of 10 submaximal (70% of 1 RM) bilateral leg curl repetitions. The
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first external testing load was half the warm-up weight. The test was performed with two
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trials on each leg with maximum effort and on five weight levels. The weight was increased
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by 2.5 kg to 5 kg with two minutes of rest between trials. The five loads assessed were
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between 40% and 70% of the individual’s 1 RM. On a given signal, the subject was asked to
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flex his or her knee as quickly and as forcefully as possible from full knee extension to
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approximately 110º knee flexion. The distance the weight stack was lifted and the time it took
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to fully flex the knee were measured with a linear encoder connected to the machine’s weight
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stack. After the five trials the maximum average power was calculated by the Muscle Lab.
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Knee-extension power test
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The knee-extension power test (Neeter et al., 2006) was performed on a knee-extension
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weight-training machine (Leg Extension 101 SE, Nordic Gym, Bollnäs, Sweden). The same
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procedure as that for the knee-flexion power test was used. The test was performed from
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approximately 110º knee flexion to full knee extension.
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Statistical Analyses
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No power calculation was performed prior to this study, instead the number of subjects was
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estimated based on that the number of individuals * the number of tests shouldn’t be less than
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25 (Bruton et al., 2000). For data on participants’ characteristics, mean and standard deviation
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(SD) were calculated. A paired-sample t-test was used to assess systematic changes between
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the two tests. To check for systematic bias, outliers, and heteroscedasticity, the data were
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visualized in Bland and Altman plots (Bland & Altman, 1986). Relative reliability; the
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intraclass correlation coefficient, was assessed by ICC2.1 (Atkinson & Nevill, 1998; Lexell &
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Downham, 2005). Absolute reliability was calculated with the standard error of measurement
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(SEM), SEM%, a measure of repeatability and repeatability percentage. SEM was defined as
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the within-subject standard deviation, that is the square root of the within-subject variance
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(WMS)
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Downham, 2005). The SEM and SEM% can be used to determine the limit for the smallest
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real difference (SRD). To determine the SRD, a measure of repeatability (Lexell & Downham,
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2005) and repeatability as a percentage of the mean were calculated according to these
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formulas: Repeatability =
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, and further,
(Atkinson & Nevill, 1998; Lexell &
and Repeatability % =
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significant level of p < 0.05 was used. The 95% limits of agreement for all the test variables
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were calculated as the inter trial mean difference ± 1.96 SD. All calculations were performed
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using SPSS for Windows (release 20.0).
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RESULTS
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Absolute values for the tests are shown in Table 1. No significant differences were found in
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any of the tests when comparing the absolute values of tests 1 and 2, except for the side-hop
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test, left leg (P = 0.01).
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Table 1 (about here)
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Good to excellent test-retest reliability (ICC2.1:0.84-0.98) was found in all tests for the left and
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right legs. Absolute values in SEM for the six tests are shown in Table 2. The SEM (%)
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ranged between 3.4 and 11.1 for the hop tests and between 8.1 and 12.4 for the power tests
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(Table 2). The smallest real differences (SRD) for the hop tests ranged between 9.3% and
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30.7% and between 24.1% and 34.3% for the three power tests (Table 2). Bland and Altman
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plots for all tests can be found as supplementary electronic data.
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Table 2 (about here)
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DISCUSSION
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To our knowledge this is the first study to examine the absolute reliability and, further, the
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SRD for the knee-flexion, knee-extension, and single-leg squat-jump tests in terms of power.
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The absolute agreement calculated with the ICC2.1 model was high, 0.88-0.96 (Vincent,
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1994). Further, the ICC for the vertical jump, the hop for distance, and the side-hop tests
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ranged from good to high absolute agreement, 0.84-0.98. In addition, the 95% CI for all
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included tests, right and left leg, was narrow, indicating good agreement.
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The ICC includes the variance term for individuals and is therefore affected by sample size
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heterogeneity, meaning that a high correlation can still mean unacceptable measurement error
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(Atkinson & Nevill, 1998). In the present study we therefore further analyzed the absolute
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agreement, which is unaffected by the range of measurements. One indicator of absolute
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reliability or the measurement variability is the SEM (Lexell & Downham, 2005). The smaller
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the SEM, the more reliable the measurement, which is often used to interpret the results of an
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improvement after an intervention. The reported SEM% for the six tests in the present study
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ranged from 3.4% to 12.4%, demonstrating that an improvement that is smaller does not
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indicate a clinically important improvement. The SEM data in the present study regarding the
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vertical jump, the hop for distance, and the side hop align closely with previously reported
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data (Neeter et al., 2006). For the knee-extension and the knee-flexion tests, our data reveal
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somewhat higher methodological error compared to those reported by Neeter et al. (2006) and
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for the newly developed more complex exercise, the single-leg squat jump, the average
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SEM% for left and right leg was 9.1%, representing approximately 75 Watt. However, it is
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important to take into consideration that several statistical assumptions are involved when
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calculating the SEM (Atkinsson & Nevill, 1998). In the literature there is no clarity regarding
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an acceptable SEM; instead, one must consider in what context the measurement is used and
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what is clinically acceptable.
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The smallest real difference (SRD) or repeatability is one way to statistically describe or
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express a measurement’s clinometric property, not to be confused with clinically important
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changes (Bland and Altman, 1986; Lexell & Downham, 1995; Turner et al., 2012). Minimal
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clinically important changes (MIC) should rather be chosen arbitrarily, referred to what
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clinicians, scientist, and patients’ rate as an important change or one that affects an individual
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functional performance (Lexell & Downham, 2005; Turner et al., 2012). According to
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analysis in the present study, it is important to determine the 95% CI in order to present a
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useful reference range. If no arbitrarily chosen MIC is available for the method of interest, it
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is recommended that SEM be used to approximate a small change (Turner et al., 2012)
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between two different measures, such as before and after an intervention period.
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To isolate and detect strength deficiency of the hamstrings- or the quadriceps musculature is
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of great importance after knee rehabilitation since a history of previous injury has been
266
associated with sustaining a new injury (Alonso et al., 2012). Further, it has been found that
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biomechanical measures during landing and postural stability can predict second anterior
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cruciate ligament injury after anterior cruciate ligament reconstruction and return to play
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(Paterno et al., 2010). The importance of testing single-leg squat motions as well as single-leg
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hops, and landing function has lately been advocated by many authors (Myer et al., 2006;
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Tagesson & Kvist, 2007; von Porat, Holmström, & Roos, 2008). Gustavsson et al. (2012)
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found abnormal symmetry in five different one-legged hop tests ranging from 43 to 77% for
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patients with an ACL injury (11 months post injury) and from 51 to 86% for patients who had
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undergone ACL reconstruction (6 months post operatively), respectively. The squat jump on
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two legs is commonly used for training and testing power among athletes, especially in sports
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involving acceleration movements such as sprinting, jumping, and throwing (Escamilla, 2001;
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Peterson et al., 2006), however, the single-leg squat simulates to a higher extend, a common
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athletic position requiring control of the body over the single fixed lower leg (Schoenfeld,
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2010; Trulsson, Garwicz, & Agerberg, 2010; Zätterström, Fridén, Lindstrand, & Moritz,
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2000). Neeter et al. (2006) studied a single-legged squat with the subjects in a supine position
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(leg press), and is therefore probably less sport-specific, since squatting in a standing position
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puts higher demands on trunk stability and coordination. One might therefore expect to see
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lower ICC values in standing position compared to lying down. Our study confirms this
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hypothesis, showing somewhat lower ICC, 0.88-0.93, compared to that found by Neeter et al.
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(2006), 0.94-0.98.
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The low number of included subject in the present study can be considered as a limitation,
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however a commonly described advise in the literature is that the number of individuals * the
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number of tests, shouldn’t be less than 25 (Bruton et al 2000; Chinn 1991), in our study 28.
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No power calculation was performed prior to the study, instead we were concerned with the
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degree of agreement, so that this problem is one of estimation rather than hypothesis testing,
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meaning we do not expect any differences between test one and test two.
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CONCLUSIONS
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The absolute reliability of this test protocol was clinically acceptable when testing healthy
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athletes, with good to excellent ICC values and measurement errors of approximately 10%.
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The test battery reflects athletic performance involving jumping movements with and without
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external loading (a single-leg squat) and leg power. The feasibility of the instrument for
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injured athletes is not known, but this test battery can be recommended for determining
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whether an athlete is ready to return to sport after an injury, since several of the involved tests
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are highly sport specific. The most sport-specific test, the single-leg squat jump, is also
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recommended as a preseason test for athletes involved in sports that require power and
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jumping qualities.
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CONFLICTS OF INTEREST AND SOURCE OF FUNDING We have no conflicts of interest and no external funding has been received for this study.
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ACKNOWLEDGMENTS We would like to acknowledge all the study participants and thank them for sharing their time
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Tables Table 1: Absolute values for the right (R) and left (L) leg (n=14) for the vertical jump, hop for distance, side hop, single-legged squat jump, knee flexion and knee extension tests. Mean and Standard Deviation (SD) is presented. Mean (SD) Test 2
Difference Test 1-Test 2 (SD) Vertical jump (cm), R 17.2 (5.3) 17.3 (5.4) 0.1 (0.9) Vertical jump (cm), L 17.1 (5.0) 17.3 (5.5) 0.2 (0.8) Hop for distance (cm), R 141.3 (29) 144.5 (25.9) 3.2 (6.6) Hop for distance (cm), L 143.1 (28.4) 146.5 (27.5) 3.4 (6.9) Side hop (no/30s), R 47.0 (12.8) 49.6 (13.5) 2.6 (7.4) Side hop (no/30s,) L 45.1 (12.6) 47.4 (13) 2.3 (2.9) Single-legged squat jump (Watt), R 810.2 (214.2) 848.9 (216.7) 38.7 (98.2) Single-legged squat jump (Watt), L 804.5 (212.3) 823.3 (233.4) 18.8 (111.4) Knee flexion (Watt), R 168.7 (64.1) 176.1 (58.9) 7.4 (19.0) Knee flexion (Watt), L 156.5 (54.4) 163.7 (49.3) 7.2 (19.6) Knee extension (Watt), R 212.7 (74.8) 220.1 (85.2) 7.4 (28.3) Knee extension (Watt), L 215.5 (95.8) 213.6 (74.8) - 1.9 (39.0)
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0.84 0.43 0.09 0.09 0.22 0.01** 0.16 0.54 0.17 0.19 0.34 0.86
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Table 2. Relative and Absolute reliability of the six included tests for left (L) and right (R) leg (n=14). (Intra Class Correlation (ICC), Standard Error of Measurement (SEM), Smallest Real Difference (SRD)). SEM (%)
SRD
SRD (%)
0.63 (cm) 0.58 (cm) 5.0 (cm) 5.3 (cm) 5.4 (no)
3.6
10.0
- 1,77
1,67
9.3
-1,77
1,42
9.7
-17,12
10,69
10.1
-17,92
11,21
2.5 (no) 72.3 (Watt)
5.5
1.72 (cm) 1.6 (cm) 13.9 (cm) 14.6 (cm) 14.8 (no) 7.0 (no)
8.7
200.2 (Watt)
0.97
0.9-0.99
0.97
0.89-0.99
0.84
0.58-0.94
0.96
0.79-0.99
0.91
0.74-0.97
0.88
0.67-0.96
77.0 (Watt)
9.5
0.95
0.85-0.98
8.1
0.96
0.78-0.98
13.9 (Watt) 14.3 (Watt) 20.0 (Watt) 26.6 (Watt)
0.94 0.91
0.82-0.98 0.72-0.97
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3.4 3.5 3.6
8.9 9.2
12.4
95 % SRD upper
30.7
-17,41
12,27
15.2
-9,31
4,74
24.1
-238,94
161,47
213.4 (Watt)
26.2
-232,20
194,59
38.6 (Watt) 39.6 (Watt) 55.4 (Watt) 73.7 (Watt)
22.4
-46,02
31,23
24.8
-46,85
32,44
25.6
-62,82
47,94
34.3
-71,79
75,57
M AN U
11.1
SC
0.95-0.99
95 % SRD lower
RI PT
SEM
0.98
EP
Vertical jump (cm), R Vertical jump (cm), L Hop for distance (cm), R Hop for distance (cm), L Side hop (no/30s), R Side hop (no/30s,) L Single-legged squat jump (Watt), R Single-legged squat jump (Watt), L Knee flexion (Watt), R Knee flexion (Watt), L Knee extension (Watt), R Knee extension (Watt), L
ICC2.1 95 % CI (lowerupper bound) 0.98 0.94-0.99
TE D
Tests
RI PT
ACCEPTED MANUSCRIPT
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Figure 1a and 1b. The single-leg squat jump, starting and flight position.
ACCEPTED MANUSCRIPT
HIGHLIGHTS FOR REVIEW Three hop tests, two leg-power tests and the single-leg squat jump were evaluated.
•
The ICC of this test battery was good to excellent (0.84-0.98)
•
The ICC for the newly developed single-leg squat jump was high (0.88-0.91).
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The measurement errors of approximately 10% is clinically acceptable
•
This test battery can be used for determining power in healthy athletes. .
•
Caution should be taken regarding the standardization procedure during testing.
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•
ACCEPTED MANUSCRIPT
CONFLICTS OF INTEREST AND SOURCE OF FUNDING
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We have no conflicts of interest and no external funding has been received for this study.
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The present study was approved by a local committee consisting of senior researchers at Karolinska Institutet, Departments of Neurobiology, Care Sciences and Society, division fo physiotherapy. Ethical considerations in the study have followed the recommendations Harris
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and Atkinson (Harris & Atkinson, 2011).
ACCEPTED Bland and Altman plots for all included tests. DataMANUSCRIPT from left and right leg have been merged in figure.
3
RI PT
2
1
+2 SD
Mean
SC
0
-1
-2
-3
-4 6
8
10
12
14
M AN U
Difference in Counter Movement Jump (test 1-2) (cm)
4
16
18
20
22
-2 SD
24
26
28
AC C
EP
TE D
Average (cm) between test and test 2, Counter Movement Jump
30
32
20
+2 SD
RI PT
10
-10
-20
80
Mean
SC
0
100
M AN U
Difference in One-legged hop test (test 1-test 2) (cm)
ACCEPTED MANUSCRIPT
120
140
160
-2 SD
180
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Average (cm) between test 1-test 2, One-legged hop hop test
200
ACCEPTED MANUSCRIPT
15 +2 SD
RI PT
10 5 0
Mean
SC
-5 -10 -15 -20 -25 10
20
M AN U
Difference Side hop test (test 1-test 2) (no of jumps)
20
30
40
50
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Average (no of jumps) test 1-test 2, Side hop test
-2 SD
60
70
ACCEPTED MANUSCRIPT
+2 SD
200
RI PT
100
0
Mean
SC
-100
-200
-300
-400 400
500
600
700
M AN U
Difference in Single-legged squat jump (test 1-test 2) (Watt)
300
800
900
1000
-2 SD
1100
1200
1300
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Average (Watt) between test 1 and test 2, Single-legged squat jump
1400
ACCEPTED MANUSCRIPT
40
RI PT
+2 SD
20
-20
-40
-60 60
Mean
SC
0
80
100
120
M AN U
Difference in Leg-Curl (test 1-test 2) (Watt)
60
140
160
180
200
220
-2 SD
240
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EP
TE D
Average (Watt) between test 1 and test 2, Leg-Curl
260
280
300
ACCEPTED MANUSCRIPT
120 100 80
+2 SD
RI PT
60 40 20 0
SC
-20 -40 -60 -80
M AN U
Difference in Leg-extension (test 1-test 2) (Watt)
140
-100 -120 -140 80
Mean
-2 SD
100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
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Average (Watt) between test 1 and test 2, Leg-extension
