IJSPT

ORIGINAL RESEARCH

HAND-HELD DYNAMOMETER POSITIONING IMPACTS DISCOMFORT DURING QUADRICEPS STRENGTH TESTING: A VALIDITY AND RELIABILITY STUDY Evan M. Hansen, PT, DPT1 Caitlyn N. McCartney, PT, DPT1 Ryan S. Sweeney, PT, DPT1 Marcus R. Palimenio, ATC1 Terry L. Grindstaff, PT, PhD, ATC, SCS1

ABSTRACT Purpose/Background: A belt-stabilized hand-held dynamometer (HHD) offers the ability to quantify quadriceps muscle strength in a clinical environment, but a limitation is participant discomfort at the interface between the HHD and the tibia. The purpose of this study was to quantify the level of discomfort associated with a modified belt-stabilized HHD configuration compared to a standard belt-stabilized configuration and an isokinetic dynamometer. The secondary purpose of this study was to determine the validity and reliability of a modified configuration used to measure quadriceps strength compared to the “gold-standard” isokinetic dynamometer. Methods: Twenty healthy participants (5 males, 15 females; age=24.7±2.2 years, height=171.1±8.8 cm, mass=72.0±18.7 kg) performed maximal knee extension isometric contractions during each of three testing conditions: isokinetic dynamometer, standard configuration with HHD placement on the tibia, and an alternative configuration with the HHD interfaced with the leg of a table. Discomfort was quantified using a Visual Analog Scale (VAS). Differences in discomfort and torque (N•m) associated with the testing positions were determined using Friedman test or repeated measures analysis of variance. Validity was quantified using Pearson correlations and within-session intrarater reliability was determined using an intraclass correlation coefficient (ICC2,1) and associated confidence intervals (95% CI). Results: The isokinetic dynamometer configuration resulted in the least discomfort (p< .01) and the modified configuration was more comfortable than the standard configuration (p= .003). There was a significant correlation between measures from the isokinetic dynamometer and the standard configuration (r=.87) and modified configuration (r=.93). Within-session intrarater reliability was good for both the standard configuration (ICC2,1=0.93) and modified configuration (ICC2,1=0.93) conditions. Conclusions: The use of the modified belt-stabilized HHD configuration, where the HHD was interfaced with the leg of a table, offers a more comfortable alternative compared to the standard belt-stabilized configuration to obtain isometric quadriceps strength measures in a clinical environment. This configuration is also a valid and reliable alternative to the “gold standard” isokinetic dynamometer when testing isometric quadriceps strength at 90° of knee flexion. Level of Evidence: Diagnostic, Level 3 Keywords: knee extension; muscle; quadriceps; torque

1

Department of Physical Therapy, Creighton University, Omaha, NE, USA

CORRESPONDING AUTHOR Terry L. Grindstaff Creighton University, School of Pharmacy & Health Professions, Physical Therapy Department, 2500 California Plaza, Omaha, NE 68178 Phone: 402-280-5674 Fax: 402-280-5692 E-mail: [email protected]

The International Journal of Sports Physical Therapy | Volume 10, Number 1 | February 2015 | Page 62

INTRODUCTION Sufficient strength of the quadriceps muscle group is necessary for functional tasks including walking, sitto-stand transfers, and climbing stairs.1-3 Quadriceps strength is positively associated with physical activity levels and quality of life.4,5 Assessment of quadriceps strength is used to guide rehabilitation progression and return to play decisions following anterior cruciate ligament injury6 and can be used to predict performance on functional tasks, such as jumping.7 Due to the importance of quadriceps strength, objective strength assessment is often sought in clinical and laboratory settings. Isokinetic dynamometers are considered the “gold standard” of strength testing8 but cost, space requirements, and portability are barriers for use among clinicians. A hand-held dynamometer (HHD) offers a relatively inexpensive, light, and portable option to obtain objective measures of muscle strength. Specific to testing quadriceps strength, a belt-stabilized HHD configuration is considered a valid (r>0.86) and reliable (ICC=0.88) estimate of strength, but this configuration tends to produce measures which are approximately 23% lower measurements compared to an isokinetic dynamometer.9 and an isokinetic dynamometer. Differences in quadriceps strength measures may be due to discomfort of the HHD against the relatively bony tibia and decreased stability of the HHD testing setup. It may be possible to modify previously described methods9 in order to reduce discomfort and to improve stability of the HHD during testing. This could be accomplished by placing the HHD against a rigid surface and allowing a padded belt to interface with the tibia. The primary purpose of this study was to quantify the level of discomfort associated with a modified belt-stabilized HHD configuration compared to a standard belt-stabilized configuration9 and an isokinetic dynamometer. The secondary purpose of this study was to determine the validity and reliability of a modified belt-stabilized HHD configuration to measure quadriceps strength compared to the “gold-standard” isokinetic dynamometer. METHODS Participants Twenty healthy participants (5 males, 15 females; age=24.7±2.2 years, height=171.1±8.8 cm, mass= 72.0±18.7 kg) volunteered for the study. The participants were fully informed of the study purpose,

procedures, and risks prior to enrollment. Inclusion criteria included age between 19 and 45 years. Exclusion criteria included history of traumatic spine or lower extremity injury within the past six months or inability to give consent or understand the procedures of the experiment. The Creighton University Institutional Review Board approved the study (IRB 14-17059) and informed consent forms. Procedures All participants completed an approved informed consent form, standardized health history form, and a self-reported form related to physical activity level (Tegner Activity Scale). Quadriceps strength (N•m) for the right leg was then measured using an isokinetic dynamometer using a refurbished Biodex System 3 Isokinetic Dynamometer (Computer Sports Medicine Inc.; Stoughton, MA). Participants were seated with their hips flexed at 85° and knees flexed at 90° (Figure 1). The chest and pelvis were secured to the chair using Velcro straps and a padded ankle strap was placed approximally five centimeters proximal to the distal aspect of the lateral malleolus. The

Figure 1. Isokinetic dynamometer set-up..

The International Journal of Sports Physical Therapy | Volume 10, Number 1 | February 2015 | Page 63

isokinetic dynamometer was interfaced with an external data acquisition system (MP150; Biopac Systems, Inc.; Goleta, CA). Participants performed a warm-up consisting of five submaximal and maximal isometric knee extension contractions (50-100% effort).10 Participants then performed three maximal isometric contractions with one minute of rest between each contraction. All maximal trials were accompanied with verbal encouragement to ensure maximal effort was achieved. Torque signals were low pass filtered at 50 Hz to remove noise. Peak torque was calculated for each maximal isometric contraction by averaging a 100 ms epoch surrounding the identified peak torque value. The highest peak torque average from a single trial was used for data analysis. Following the isokinetic dynamometer testing, patients were asked to rate their level of discomfort during testing by marking a vertical line on a 100 mm Visual Analog Scale (VAS). Next, participants transitioned to one of two HHD configurations using the microFET2, (Hoggan Scientific, LLC; West Jordan, UT): standard belt-stabilized HHD configuration or a modified standard belt-stabilized HHD (Figure 2A) configuration (Figure 2B). The order of HHD configuration was randomized. Participants were placed in a seated position with legs hanging from the edge of a wooden treatment table, with the knee in approximately 90° of flexion. A small wedge-type bolster was placed at the posterior aspect of the distal thigh to minimize posterior thigh discomfort and a strap (standard gait belt) was used to stabilize the thighs to the table (Figure 2). A

gait belt attached to the leg of the table was used to stabilize the HHD during testing and was positioned approximately 5 cm proximal to the distal aspect of the lateral malleolus, consistent with isokinetic dynamometer pad placement. The standard belt-stabilized configuration positioned the HHD on the tibia, using a curved attachment (Figure 2A), which was consistent with previous methods.9 The a modified standard belt-stabilized configuration positioned the HHD against the back of a treatment table leg using a flat attachment (Figure 2B). A foam pad was placed across the anterior aspect of the tibia and the gait belt was looped through the pad and secured the HHD against the leg of the table. When the participant extended his or her knee, the HHD was compressed against the table leg and force could be measured. For both HHD configurations, participants were asked to extend their knees in a similar manner as the isokinetic dynamometer testing to obtain three separate maximal isometric contractions. One minute of rest was provided between each contraction. All maximal trials with the HHD were also accompanied by verbal encouragement to ensure maximal effort was achieved. Maximal isometric force (N) was recorded for each trial. To calculate torque, a measure was taken, in centimeters, from the lateral knee joint line (estimated knee axis of rotation) to the point five centimeters proximal to the distal aspect of the lateral malleolus. This value was then multiplied by the amount of force (N) recorded by the HHD to obtain torque (N•m). The highest peak torque from a single trial for each HHD configuration was used for data analysis. After each HHD configuration, participants recorded their level of discomfort during testing using a VAS. Participants were then provided a 10-minute rest break. After the rest break, both HHD configurations were repeated using the same methods. This data was used to estimate within-session intrarater reliability for both HHD configurations.

Figure 2. A) Standard belt-stabilized HHD configuration B) Modified belt-stabilized HHD configuration.

Statistical Analysis The independent variable was testing method (isokinetic dynamometer, standard configuration, modified configuration) and the outcome variables were discomfort (VAS) and torque (N•m). Differences in discomfort (VAS) between the testing positions

The International Journal of Sports Physical Therapy | Volume 10, Number 1 | February 2015 | Page 64

was determined using a Friedman test. Validity was quantified using Pearson correlations and examining differences in torque (N•m) between testing conditions using a repeated measures analysis of variance. Bland-Altman Plots with Limits of Agreement (LOA) calculations11 were used to graphically display differences between conditions and provide insights into systematic bias between measurement techniques. Within-session intrarater reliability was determined using the repeated measures ANOVA, intraclass correlation coefficient (ICC2,1), and associated confidence intervals (95% CI). To provide better interpretation of reliability estimates, the authors also calculated the standard error of measurement (SEM) (SEM=SD √1-ICC)12 and minimal detectable change (MDC) (MDC=SEM * 1.96* √2).12 Within-session intrarater reliability for HHD measures was interpreted as follows: 0.75 good.13 Alpha level was set a priori at p < 0.05. When significance was achieved relevant post-hoc tests were performed to determine differences between conditions. Statistical analyses were performed with SPSS Version 20.0 (SPSS Inc., Chicago, IL).

Table 2. Torque-Generating capacity (N·m) differences between the three HHD configurations. Values are mean ± standard deviation. Trial 1 252.6 ± 82.8 Isokinetic Dynamometer Torque (N·m) 208.9 ± 69.2* Standard Belt-Stabilized HHD Torque (N·m) 248.5 ± 79.2 Modified Belt-Stabilized HHD Torque (N·m) * significantly less torque (p < .001) than isokinetic dynamometer and the modified belt-stabilized configuration.

(p

Hand-held Dynamometer Positioning Impacts Discomfort During Quadriceps Strength Testing: A Validity and Reliability Study.

A belt-stabilized hand-held dynamometer (HHD) offers the ability to quantify quadriceps muscle strength in a clinical environment, but a limitation is...
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