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European Journal of Sport Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejs20
Effect of movement speed on trunk and hip exercise performance a
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Jose L. L. Elvira , David Barbado , Belen Flores-Parodi , Janice M. Moreside & Francisco J. a
Vera-Garcia a
Sports Research Centre, Miguel Hernandez University of Elche, Alicante, Spain
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School of Physiotherapy, Dalhousie University, Halifax, Canada Published online: 22 Nov 2013.
To cite this article: Jose L. L. Elvira, David Barbado, Belen Flores-Parodi, Janice M. Moreside & Francisco J. Vera-Garcia (2014) Effect of movement speed on trunk and hip exercise performance, European Journal of Sport Science, 14:6, 547-555, DOI: 10.1080/17461391.2013.860483 To link to this article: http://dx.doi.org/10.1080/17461391.2013.860483
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European Journal of Sport Science, 2014 Vol. 14, No. 6, 547–555, http://dx.doi.org/10.1080/17461391.2013.860483
ORIGINAL ARTICLE
Effect of movement speed on trunk and hip exercise performance
JOSE L. L. ELVIRA1, DAVID BARBADO1, BELEN FLORES-PARODI1, JANICE M. MORESIDE2, & FRANCISCO J. VERA-GARCIA1 Sports Research Centre, Miguel Hernandez University of Elche, Alicante, Spain, 2School of Physiotherapy, Dalhousie University, Halifax, Canada
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Abstract The influence of speed on trunk exercise technique is poorly understood. The aim of this study was to analyse the effect of movement speed on the kinematics and kinetics of curl-up, sit-up and leg raising/lowering exercises. Seventeen healthy, recreationally trained individuals (13 females and 4 males) volunteered to participate in this study. Four different exercise cadences were analysed: 1 repetition/4 s, 1 repetition/2 s, 1 repetition/1.5 s and 1 repetition/1 s. The exercises were executed on a force plate and recorded by three cameras to conduct a 3D photogrammetric analysis. The cephalo-caudal displacement of the centre of pressure and range of motion (ROM) of six joints describing the trunk and hip movements were measured. As sit-up and curl-up speed increased, hip and knee ROM increased. Dorsal-lumbar and upper trunk ROM increased with speed in the curl-up. Faster cadence in the sit-up exercise had minimal effect on trunk ROM: only the upper trunk ROM decreased significantly. In the leg raising/lowering exercise there was a decrease in the pelvic tilt and hip ROM, and increased knee flexion ROM. During higher speed exercises, participants modified their technique to maintain the cadence. Thus, professionals would do well to monitor and control participants’ technique during high-speed exercises to maintain performance specificity. Results also suggest division of speed into two cadence categories, to be used as a reference for prescribing exercise speed based on preferred outcome goals. Keywords: Biomechanics, 3D analysis, kinetics, core training
Introduction Core exercises are widely used in clinical, recreational and sport settings to achieve various goals. Examples comprise improved spine stability for back injury prevention or rehabilitation (Borghuis, Hof, & Lemmink, 2008; McGill, 2002; Smith, Nyland, Caudill, Brosky, & Caborn, 2008), increased muscle strength and power in professional athletes (McGill, 2004) and developed muscular endurance in high school physical education students (Vera-Garcia, 2003). Research on core exercises has mainly focused on assessing exercise effectiveness and safety by analysing trunk muscle recruitment (Monfort-Pañego, Vera-Garcia, Sanchez-Zuriaga, & Sarti-Martinez, 2009) and spine loads (Axler & McGill, 1997; Kavcic, Grenier, & McGill, 2004), respectively. Consequently, a large number of biomechanical studies have evaluated the effect of various factors of trunk exercise performance on muscle response and/or
spinal loading: spine and hip flexion, (Axler & McGill, 1997; Juker, McGill, Kropf, & Steffen, 1998), trunk rotation and bending (Axler & McGill, 1997; Juker et al., 1998; McGill, 1991; Vera-Garcia, Moreside, & McGill, 2011), supported segments (Andersson, Nilsson, Ma, & Thorstensson, 1997; Guimaraes, Vaz, De Campos, & Marantes, 1991), arm and hand position (Alexander, 1985; Knudson, 1999), knee and hip position, (Andersson et al., 1997; Axler & McGill, 1997; García-Vaquero, Moreside, Brontons-Gil, Peco-Gonzalez, & Vera-Garcia, 2012), movement of upper vs. lower body, (Lehman & McGill, 2001; Sarti, Monfort, Fuster, & Villaplana, 1996; Vera-Garcia, Moreside, & McGill, 2010; VeraGarcia et al., 2011), the use of equipment (Marshall & Murphy, 2005; Moreside, Vera-Garcia, & McGill, 2007; Sánchez-zuriaga, Vera-Garcia, Moreside, & McGill, 2009; Vera-Garcia, Grenier, & McGill, 2000), movement speed (Godfrey, Kindig, & Windell, 1977;
Correspondence: J. L. L. Elvira, Sports Research Centre, Universidad Miguel Hernández de Elche, Avda. de la Universidad, S/N.03202 Elche, Alicante, Spain. E-mail: [email protected] © 2013 European College of Sport Science
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Vera-Garcia, 2003; Vera-Garcia, Flores-Parodi, Elvira, & Sarti, 2008), etc. Speed of movement, controlled by the movement cadence, is one of the variables that can be easily modified to adjust the intensity of the exercises. Vera-Garcia et al. (2008) reported an increase in the activation and co-activation of the trunk muscles when increasing the speed of curl-up or crunch exercises. Similarly, Godfrey et al. (1977) found higher durations of rectus abdominis and external oblique activation during fast sit-up exercises compared to slow sit-ups. However, scientific evaluation of the influence of movement speed on trunk exercise technique is lacking. An increase in the speed of movement implies an increase in segmental angular momentum, and potentially modified range of motion (ROM) of the principal joints (Bruijn, Meyns, Jonkers, Kaat, & Duysens, 2011). In addition, it is expected that a threshold cadence exists, after which the movement is no longer controlled by the agonist muscles only, but requires associated plyometric contractions from both the agonist and antagonist muscles. This rapid alternating between segmental acceleration and deceleration may result in altered movement patterns and muscle lengths compared to a slower cadence. In turn, muscles may be working in different force–length relationships than those expected, thus resulting in modified exercise effects. The aim of this hypothesis-driven study was to analyse the effect of movement speed on the kinematics and kinetics of three commonly used trunk and hip strengthening exercises: curl-up, sit-up and double leg raising/lowering. Specifically, we were interested in identifying variations in exercise technique resulting from speed increases, which may subsequently impact training results.
Methods Subjects An a-priori power analysis was conducted to estimate the sample size. GPower software (GPower 3.1.7, Kiel University, Germany) estimated a sample size of 14 subjects (effect size with partial eta squared, g2p ¼ 0.25; significance level = 0.05; required power = 0.80; correlation among repeated measures = 0.30). Seventeen healthy participants, 13 females and 4 males (mean age = 23.6, s = 4.4 years; height = 166.3, s = 6.5 cm; mass = 61.0, s = 8.4 kg) were recruited from the university setting. All participants were healthy, without current hip or back pain or past pathology in these regions. Each participant was recreationally trained, defined as participating in noncompetitive physical activities such as jogging,
swimming, cycling and resistance exercises at least three times per week, for a minimum of 30 min per session. Similarly, each reported participation in core training exercises (i.e., common trunk and hip strengthening and endurance exercises) at least one session per week. Written informed consent was obtained from each participant prior to testing. The experimental procedures used in this study were in accordance with the Declaration of Helsinki and were approved by the University Office for Research Ethics. Procedures Participants were instructed in the execution of the three exercises (curl-up, sit-up and leg raising/lowering). For the curl-up and the sit-up performance, they were required to lay on a force platform (600 × 370 mm, Dinascan 600M, IBV, Valencia, Spain) in a supine position with arms crossed in front of the chest, and shoulders flexed and internally rotated 90° (Figure 1a and b). A 0.6 cm thick fitness mat with the same dimensions as the force platform was affixed atop the platform to increase the participants’ comfort and prevent slipping from the initial position. In the curl-up, participants were to raise their head and shoulders off the platform, but not lift further than the inferior scapular borders (Figure 1a). The emphasis was in curling the upper thoracic spine forwards in the sagittal plane. In the sit-up, participants were instructed to raise their upper body to a point where they could touch their knees with their elbows, while their ankles were secured by the investigator (Figure 1b). The leg raising/lowering exercise required each supine participant to raise both lower limbs simultaneously until the feet touched a bar, indicating the vertical position, while maintaining knee extension (Figure 1c). The participants stabilised their upper body position by grasping the ankles of the investigator (Figure 1c). One complete repetition of each exercise included both raising and lowering of the body segment. Ten repetitions of each were performed sequentially. Three cadences were tested for each exercise: 1 repetition/4 s (C4), 1 repetition/2 s (C2) and 1 repetition/1.5 s (C1.5). The curl-ups were also performed at 1 repetition/1 s (C1), but this cadence was found to be too fast for the other two exercises. A metronome was used to pace the cadence. Participants were instructed to carry out all exercises with a constant and fluid motion. The order of the exercises was randomised, resting 3 min between cadences and 5 min between exercises. Speed conditions were ordered from lowest to highest for each exercise, as had previously been determined as the optimal order for participants to adapt to betweentrial cadence changes.
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Effect of movement speed on exercise performance
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Figure 1. Initial and final positions of each of the three exercises being tested. One complete repetition included a return to the start position. Subjects were instructed to perform at a constant speed and fluid motion, while cadence was paced with a metronome.
Exercises were performed such that the region from the participant’s shoulders to pelvis was resting on the force plate, with the sagittal plane of their body aligned with the long axis of the force plate. On average, 85% of their total weight was resting on the force plate in the initial position. After each exercise and cadence, participants were repositioned on the force plate. Ground reaction forces were recorded at 500 Hz, and centre of pressure (COP) of the body lying on the force plate in the cephalo-caudal direction was calculated. Three digital cameras (Canon XM1, Sony DCRTRV33 and Sony SSC-DC338), recording at 50 Hz, were placed at 0°, 45° and 90° from the sagittal plane. The reference frame used was a prism of 2 × 1 × 1 m. Reflective markers were placed on the following anatomical landmarks on the right side of the body: lateral malleolus, lateral femoral condyle, greater trochanter, anterior superior iliac spine, mid-
point between the anterior superior iliac spine and posterior superior iliac spine, mid-point of the lowest rib, inferior lateral angle of the scapula and acromion (Figure 2a). Markers were automatically digitised and reconstructed using standard photogrammetry algorithms (Kwon 3D software: Visol Inc., Korea). A six segment model was used. The following angles pro‐ jected in the sagittal plane were calculated (Figure 2b): . . .
Upper trunk with the horizontal (UTH): angle between acromion-scapula segment compared to the horizontal. Dorsal flexion (DF): angle between scapulalowest rib segment compared to the acromion-scapula segment. Dorsal-lumbar flexion (DLF): angle between scapula-lowest rib segment and lowest ribmid-point between the anterior superior iliac spine segment.
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Figure 2. A model of eight points and six segments was used. (a) Anatomical markers: LM: lateral malleolus; LFC: lateral femoral condyle; T: trochanter; ASIS: anterior superior iliac spine; MPSIS: mid-point between the ASIS and posterior superior iliac spine; LR: lower rib; S: inferior angle of the scapula; AC: acromion. (b) Measured angles: UTH: upper trunk with the horizontal; DF: dorsal flexion; DLF: dorsallumbar flexion; PT: pelvic tilt; H: hip; K: knee.
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Pelvic tilt (PT): angle between lowest rib-midpoint between the anterior superior iliac spine segment and mid-point between the anterior superior iliac spine-anterior superior iliac spine segment. Hip (H): angle between lateral femoral condyle-greater trochanter segment compared to mid-point between the anterior superior iliac spine-anterior superior iliac spine segment. Knee (K): angle between lateral malleoluslateral femoral condyle segment and lateral femoral condyle-greater trochanter segment.
In the leg raising/lowering exercise, the upper trunk angles UTH and DF were not reported as their movement was negligible. Despite the fact that 10 repetitions were performed, only 5 repetitions (usually 4 through 8) were used for analysis; the first repetitions were discarded to ensure the participants were in time with the cadence, and the last repetitions removed to diminish the possibility of fatigue influencing the movement pattern. For each of the six angles, total ROM and COP displacement were averaged over the five trials, then the mean calculated across all participants.
Statistical analyses To ensure that sex did not influence the results, we conducted an exploratory statistical comparison between males and females: a mixed ANOVA for each exercise and variable, with speed as the withinsubject factor and sex the between-subject factor. Results indicate that sex does not significantly affect speed (P > 0.05) in any of the variables and exercises. In order to evaluate the possibility of the trunk slipping on the platform while performing the exercises, a repeated measures ANOVA was used to compare the minimum and maximum displacement of the COP (initial and final COP position, respectively) between repetitions for each exercise and speed. In addition, the intraclass correlation coefficient (twoway random effects model) was calculated to assess the relative reliability between repetitions for the minimum, maximum and total displacement of the COP, and the standard error of measurement to assess the absolute reliability between repetitions for the total COP displacement. The standard error of measurement was not performed for minimum and maximum COP displacement because they are arbitrary values that depend on the participant’s dimensions. Intraclass correlation coefficients for
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Effect of movement speed on exercise performance maximum, minimum and total COP displacement ranged between 0.85 and 0.96 across exercises and speeds. Standard errors of measurement for total COP displacement ranged between 4 and 8%. Finally, repeated measures ANOVA did not find statistical differences for the initial and final COP position between repetitions in any trial. Overall, these results demonstrate the reliability of the measurements, indicating that the trunk did not slip on the force platform while preforming the exercises at different speeds. To evaluate the effect of movement speed on the kinematics and kinetics of curl-up, sit-up and leg raising/lowering exercises, a repeated measures ANOVA with cadence as a factor was performed for each exercise. Bonferroni post hoc tests with a significance level chosen at P < 0.05 were carried out to allow within-exercise cadence comparisons. No between-exercise comparisons were made because the mass and radius of gyration were not comparable between exercises, despite similar cadences. Partial eta squared (g2p ) was also calculated as a measure of effect size and proportion of the overall variance that is attributable to the factor. Values of effect size ≥0.64 were considered strong, around 0.25 were considered moderate and ≤ 0.04 were considered small (Ferguson, 2009). All analyses utilised the SPSS package version 20.0 (IBM SPSS Inc., Chicago, IL, USA). Results The averages for the COP displacement and ROM of the aforementioned angles are shown in Table I. See Figure 3 for a pictorial representation of the changes in the initial and final position, comparing slowest and fastest cadence. Results indicate that, in all three exercises, a faster cadence elicited greater displacement of the COP (P < 0.001). In the curl-up exercise, increasing speed resulted in significantly greater ROM of all angles except DF. The largest changes were seen in the DLF and UTH ROM, which increased an average of 8.4° and 7.6°, respectively. During the sit-up, the hip and knee ROM increased an average of 5.0° and 3.4°, respectively, with increasing speed, whereas UTH decreased an average of 8.4°. As speed increased in the leg raising/lowering exercise, mean PT and hip flexion ROM decreased (2.9 and 2.7°, respectively), while average knee ROM increased a substantial 8.5°. Discussion A common problem in sports training and exercise is the ability to control the intensity of the activity. Given that training effects are specific to
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performance velocity (Kanehisa & Miyashita, 1983), some athletes require high-speed exercises and plyometrics to improve performance (McGill, 2004). One of the training variables that can easily be manipulated to modulate the intensity of trunk exercises is the speed of movement (Vera-Garcia et al., 2008), which can be adjusted by the cadence of the exercise. In the present study, the effects of movement speed on three conventional trunk and hip strengthening exercises were analysed. It was anticipated that increases in angular momentum due to the higher speed would cause an increase in trunk motion. This is supported by the significant increase in the COP displacement in all exercises (Table I). However, the effect of velocity on angular ROM differed between exercises. It should be noted that this study was conducted on healthy, young volunteers, and may not reflect movement strategies that would be adopted in different populations, such as those with low back pain, different age groups or varying athletic abilities. Curl-up In the curl-up, flexion is focused in the mid-thoracic region, as measured by DF. Increasing the cadence did not modify DF ROM, therefore the focus of the exercise appears to remain the same. However, the UTH angle increased with each faster cadence (P < 0.001, g2p ¼ 0.493), thus demonstrating an increase in the overall upper trunk movement relative to the ground. This can be explained by the increase in DLF (P < 0.001, g2p ¼ 0.555), which appears to be a side effect of increasing the angular momentum due to the increase in the angular velocity. This exercise had no tactile end goal at the end of the upwards phase: unlike the sit-up or leg raising/lowering, participants were not aiming to reach their knees or a bar. Consequently, with increasing speed, there may have been less specificity as to the end point of the exercise, resulting in greater flexion throughout the spine, and possibly lifting the lower scapular borders off the platform (Figure 3a). Repetitive lumbar flexion is known to be potentially injurious to the intervertebral discs (Callaghan & McGill, 2001; Nachemson, 1966), thus, this change in technique associated with higher speeds should be closely monitored. Increasing curl-up speed was also associated with corresponding increases in COP displace‐ ment (P < 0.001, g2p ¼ 0.804) and PT (P < 0.001, g2p ¼ 0.493), considered to be strong and moderate effect sizes, respectively. The increase in PT ROM may be interpreted as a consequence of activating the trunk extensor muscles while relaxing the flexors at the end of the upwards movement to facilitate rapid deceleration and downwards acceleration of trunk
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Table I. Average angular range of motion (degrees) and centre of pressure displacement (cm) at each cadence (C4: 1 repetition/4 s; C2: 1 repetition/2 s; C1.5: 1 repetition/1.5 s; C1: 1 repetition/1 s)
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Variables
C4
Curl-up COP 11.6 UTH 40.2 DF 31.2 DLF 18.7 PT 8.8 Hip 3.7 Knee 1.1 Sit-up COP 33.4 UTH 107.8 DF 23.2 DLF 23.6 PT 33.9 Hip 37.6 Knee 12.8 Leg raising/lowering COP 21.6 DLF 10.9 PT 31.7 Hip 58.3 Knee 11.4
C2
C1.5
C1
Partial eta squared
< 0.001 < 0.001 0.288 < 0.001 < 0.001 0.028 < 0.001
0.804 0.493 0.075 0.555 0.493 0.174 0.716
± ± ± ± ± ± ±
3.5 7.2 6.5 6.7 3.4 2.6 1.0
14.8 42.0 30.8 21.6 10.3 3.7 1.7
± ± ± ± ± ± ±
3.8A 5.3 6.8 7.0A 3.0A 1.8 1.3
23.1 45.3 32.1 23.9 11.4 4.0 2.8
± ± ± ± ± ± ±
4.1AB 7.0AB 7.8 6.0A 4.8AB 2.5 1.9AB
23.0 47.8 32.3 27.1 14.1 5.6 4.2
± ± ± ± ± ± ±
4.0 9.5 7.0 8.1 7.2 6.8 3.7
35.8 106.8 23.2 24.9 31.3 39.9 15.0
± ± ± ± ± ± ±
6.7 10.4 8.9 8.0 7.0 7.7A 3.5A
40.0 99.4 19.4 23.3 30.4 42.6 16.2
± ± ± ± ± ± ±
7.4AB 12.4AB 9.1 8.7 9.2 8.3AB 3.0A
– – – – – – –
< 0.001 0.001 0.067 0.443 0.053 < 0.001 < 0.001
0.408 0.372 0.155 0.045 0.167 0.476 0.489
± ± ± ± ±
2.9 5.1 8.0 8.6 5.6
26.4 11.1 31.2 58.5 14.7
± ± ± ± ±
3.6A 4.8 7.6 9.6 7.1A
35.1 12.9 28.8 55.6 19.9
± ± ± ± ±
3.7AB 5.4 8.6AB 8.0AB 12.4AB
– – – – –
< 0.001 0.065 0.006 0.001 0.004
0.916 0.174 0.275 0.361 0.374
± ± ± ± ± ± ±
4.1ABC 7.6AB 7.2 6.0ABC 4.6ABC 3.2ABC 1.9ABC
p-value
Notes: ASignificantly different from C4; BSignificantly different from C2; CSignificantly different from C1.5; (significance value of P < 0.05). COP: cephalo-caudal centre of pressure displacement; UTH: angle of upper trunk with the horizontal; DF: dorsal flexion angle; DLF: dorso-lumbar angle; PT: pelvic tilt; Hip: hip angle; Knee: knee angle (see document and Figure 2 for more complete descriptions).
motion at the higher cadences. Nevertheless, further research is necessary to confirm this hypothesis. Increasing cadence also resulted in greater hip and knee ROM (P = 0.028, g2p ¼ 0.174, and P < 0.001, g2p ¼ 0.716, respectively), thus a different muscular activation pattern may have occurred. These changes could be due to increased angular momentum with speed, making it more difficult to slow down the trunk motion, and thus resulting in increased COP displacement and greater hip and knee ROM. It is likely that greater increases in hip and knee ROM might have occurred on a more slippery surface, thus, using some type of non-slip surface is recommended when exercising at high speeds.
Sit-up In the sit-up exercise, the main joint involved in the trunk sagittal displacement is the hip. With increasing cadence, hip ROM also increased significantly with a moderate effect size (P < 0.001, g2p ¼ 0.476). At the faster cadences, it was observed that many participants raised their pelvis while moving backwards at the end of the downwards phase (see Figure 3b), possibly in an attempt to provide extra impulse to raise the trunk in the next concentric contraction phase. This manoeuvre implied a slight hip extension (Figure 3b) that explains the ROM increases in the hip angle.
Increased hip ROM occurred without associated changes in DF or DLF, but with a significant reduction in UTH ROM in the fastest cadence. Thus, faster cadences did not affect the temporal strategy used to raise the trunk from the force plate: that of upper trunk flexion followed by a hip flexion (Cordo et al., 2003). Nevertheless, the reduction in scope of the UTH ROM may be attributed to an attempt to reduce the angular displacement of the trunk and head in the deceleration phases at the end of each upwards and downwards movement as participants struggled to maintain the higher cadences.
Leg raising/lowering In the leg raising/lowering exercise, the hip is again the main focus of movement. There were no significant changes in hip ROM between the C4 and C2 cadences, but at the fastest cadence (C1.5), hip ROM was significantly reduced. This was in conjunction with an increase in knee ROM, thus increased knee flexion, despite instructions to maintain knee extension. This may be an adaptation of the exercise technique to reduce the radius of gyration and thus the angular momentum, facilitating the ability to maintain the highest cadence. Even with significant changes in ROM, the effect size in
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Effect of movement speed on exercise performance
Figure 3. Stick figures of a representative subject performing the three analysed exercises. The initial and final positions of one repetition are shown. Solid lines represent the slowest cadence (C4); dashed lines represent the fastest cadence (C1 for curl-up exercise and C1.5 for sit-up and leg raising/lowering exercises).
both angles tended to be moderate (hip g2p ¼ 0.361 and knee g2p ¼ 0.374). Interestingly, speed increases in the leg raising/ lowering exercise caused a significant reduction in the total PT ROM (P = 0.006, g2p ¼ 0.275). This reduction occurred despite the fact that this exercise is the one in which the COP displacement was more affected by speed and had the highest effect size (P < 0.001, g2p ¼ 0.916). Although this reduction could be interpreted as a result of an increase in the trunk muscle co-activation, the reduction could have been due to other factors such as the aforementioned simultaneous reduction in hip ROM and increased knee ROM. There was also a
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nonsignificant trend for increasing cadence to result in more DLF, inferring that motion was occurring higher up the spine. Whether this motion represents increased lumbar extension or flexion, repetitive plyometric sagittal spine motion should not be recommended for patients with motor control deficits or low back disorders, nor those who are untrained or unfit, due to the possibility of injury to the intervertebral discs (Aultman, Scannell, & McGill, 2005; Callaghan & McGill, 2001; McGill, 2004; Parkinson, Beach, & Callaghan, 2004). For the three exercises in general, rationale would indicate that while lower cadences require only the flexor muscles to be continuously active, both concentrically (upwards) and eccentrically (downwards), the higher cadences require the alternating activity of both flexor and extensor muscles to be able to maintain the cadence (plyometric contraction, slowing down eccentrically and accelerating concentrically). This has been shown previously for the curl-up exercise (Vera-Garcia et al., 2008), and similar muscle responses could be expected for the sit-up and leg raising/lowering exercises. Based on the number of statistical differences found, it appears that C4 and C2 fit into the ‘lower cadence’ category, while C1.5 and C1 could be considered ‘higher cadence’ due to the ensuing changes in motion patterns. This cadence division could potentially be considered as a reference for prescribing exercise speed, based on preferred outcome goals. Lower cadences may be more appropriate for a clinical rehabilitation setting as patients may be especially sensitive to spine loading magnitudes. In that trunk dynamics have a significant impact on spinal loads (Davis & Marras, 2000) there may be a need to control exercise speed in clinical settings to reduce risk of injury. Conversely, higher cadences may be recommended in a sport environment in which participants are seeking more power and plyometric contractions to challenge the neuromuscular system in a way that is similar to that of competition (Vera-Garcia et al., 2008). These results indicate that performance technique during three specific trunk exercises changed with the speed of movement. Most of the changes seem to be due to the participants’ difficulty in keeping up with higher cadences (especially C1.5 and C1). The higher speeds require fast plyometric contractions, which entail altered motor control and specific motion patterns. Thus, it appears that as cadence increases, the focus changes from one of technique to that of maintaining a specific speed, resulting in altered kinetics and kinematics. In addition, not only do these three exercises have different goals but also these can be further subdivided by cadence, to increase exercise outcome specificity. As a reference, up to a 2-s cadence can be considered as ‘low’ and
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faster cadences as ‘high’. While the former may be more appropriate for a rehabilitation setting, the higher speeds may be more relevant in a sports environment. However, exercise cadence is a variable that requires close monitoring and correction, as technique alterations will likely ensue. Professionals utilising trunk and hip strengthening exercises should bear this in mind when designing exercise programmes. Acknowledgements
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This study was made possible by financial support from Universidad Miguel Hernández de Elche (Bancaja-UMH 2009), Spain and Universidad Católica San Antonio de Murcia (PMAFI-PI-02/ 1C/04), Spain. References Alexander, M. J. L. (1985). Biomechanics of sit-up exercises. CAHPER Journal, 51, 36–38. Andersson, E. A., Nilsson, J., Ma, Z., & Thorstensson, A. (1997). Abdominal and hip flexor muscle activation during various training exercises. European Journal of Applied Physiology and Occupational Physiology, 75(2), 115–123. doi:10.1007/s0042 10050135 Aultman, C. D., Scannell, J., & McGill, S. M. (2005). The direction of progressive herniation in porcine spine motion segments is influenced by the orientation of the bending axis. Clinical Biomechanics, 20(2), 126–129. doi:10.1016/j.clinbiom ech.2004.09.010 Axler, C. T., & McGill, S. M. (1997). Low back loads over a variety of abdominal exercises: Searching for the safest abdominal challenge. Medicine and Science in Sports and Exercise, 29, 804–811. doi:10.1097/00005768-199706000-00011 Borghuis, J., Hof, A. L., & Lemmink, K. A. P. M. (2008). The importance of sensory-motor control in providing core stability: Implications for measurement and training. Sports Medicine, 38, 893–916. doi:10.2165/00007256-200838110-00002 Bruijn, S. M., Meyns, P., Jonkers, I., Kaat, D., & Duysens, J. (2011). Control of angular momentum during walking in children with cerebral palsy. Research in Developmental Disabilities, 32, 2860–2866. doi:10.1016/j.ridd.2011.05.019 Callaghan, J. P., & McGill, S. M. (2001). Intervertebral disc herniation: Studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clinical Biomechanics, 16(1), 28–37. doi:10.1016/S0268-0033 (00)00063-2 Cordo, P. J., Gurfinkel, V. S., Smith, T. C., Hodges, P. W., Verschueren, S. M. P., & Brumagne, S. (2003). The sit-up: Complex kinematics and muscle activity in voluntary axial movement. Journal of Electromyography and Kinesiology, 13, 239–252. doi:10.1016/S1050-6411(03)00023-3 Davis, K. G., & Marras, W. S. (2000). The effects of motion on trunk biomechanics. Clinical Biomechanics, 15, 703–717. doi:10.1016/S0268-0033(00)00035-8 Ferguson, C. J. (2009). An effect size primer: A guide for clinicians and researchers. Professional Psychology: Research and Practice, 40, 532–538. doi:10.1037/a0015808 Garcia-Vaquero, M. P., Moreside, J. M., Brontons-Gil, E., PecoGonzalez, N., & Vera-Garcia, F. J. (2012). Trunk muscle activation during stabilization exercises with single and double leg support. Journal of Electromyography and Kinesiology, 22, 398–406. doi:10.1016/j.jelekin.2012.02.017
Godfrey, K. E., Kindig, L. E., & Windell, E. J. (1977). Electromyographic study of duration of muscle activity in sit-up variations. Archives of Physical Medicine Rehabilitation, 58(3), 132–135. Guimaraes, A. C., Vaz, M. A., De Campos, M. I., & Marantes, R. (1991). The contribution of the rectus abdominis and rectus femoris in twelve selected abdominal exercises. An electromyographic study. Journal of Sports Medicine and Physical Fitness, 31, 222–230. Juker, D., McGill, S., Kropf, P., & Steffen, T. (1998). Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of tasks. Medicine and Science in Sports and Exercise, 30, 301–310. doi:10.1097/00005768-199802000-00020 Kanehisa, H., & Miyashita, M. (1983). Specificity of velocity in strength training. European Journal of Applied Physiology and Occupational Physiology, 52(1), 104–106. doi:10.1007/BF0042 9034 Kavcic, N., Grenier, S., & McGill, S. M. (2004). Determining the stabilizing role of individual torso muscles during rehabilitation exercises. Spine, 29, 1254–1265. doi:10.1097/00007632-20040 6010-00016 Knudson, D. (1999). Issues in abdominal fitness: Testing and technique. Journal of Physical Education, Recreation & Dance, 70 (3), 49–55. doi:10.1080/07303084.1999.10605896 Lehman, G. J., & McGill, S. M. (2001). Quantification of the differences in electromyographic activity magnitude between the upper and lower portions of the rectus abdominis muscle during selected trunk exercises. Physical Therapy, 81, 1096–1101. Marshall, P. W., & Murphy, B. A. (2005). Core stability exercises on and off a Swiss ball. Archives of Physical Medicine Rehabilitation, 86, 242–249. doi:10.1016/j.apmr.2004.05.004 McGill, S. M. (1991). Electromyographic activity of the abdominal and low back musculature during the generation of isometric and dynamic axial trunk torque: Implications for lumbar mechanics. Journal of Orthopaedic Research, 9(1), 91– 103. doi:10.1002/jor.1100090112 McGill, S. M. (2002). Low back disorders. Evidence based prevention and rehabilitation. Champaign, IL: Human Kinetics. McGill, S. M. (2004). Ultimate back fitness and performance. Waterloo, ON: Wabuno Publishers. Monfort-Pañego, M., Vera-Garcia, F. J., Sanchez-Zuriaga, D., & Sarti-Martinez, M. A. (2009). Electromyographic studies in abdominal exercises: A literature synthesis. Journal of Manipulative and Physiological Therapeutics, 32, 232–244. doi:10.1016/ j.jmpt.2009.02.007 Moreside, J. M., Vera-Garcia, F. J., & McGill, S. M. (2007). Trunk muscle activation patterns, lumbar compressive forces, and spine stability when using the bodyblade. Physical Therapy, 87, 153–163. doi:10.2522/ptj.20060019 Nachemson, A. (1966). The load on lumbar disks in different positions of the body. Clinical Orthopaedics and Related Research, 45, 107–122. doi:10.1097/00003086-196600450-00014 Parkinson, R. J., Beach, T. A. C., & Callaghan, J. P. (2004). The time-varying response of the in vivo lumbar spine to dynamic repetitive flexion. Clinical Biomechanics, 19, 330–336. doi:10.1016/j.clinbiomech.2004.01.002 Sanchez-Zuriaga, D., Vera-Garcia, F. J., Moreside, J. M., & McGill, S. M. (2009). Trunk muscle activation patterns and spine kinematics when using an oscillating blade: Influence of different postures and blade orientations. Archives of Physical Medicine Rehabilitation, 90, 1055–1060. doi:10.1016/j.apmr.200 8.12.015 Sarti, M. A., Monfort, M., Fuster, M. A., & Villaplana, L. A. (1996). Muscle activity in upper and lower rectus abdominis during abdominal exercises. Archives of Physical Medicine Rehabilitation, 77, 1293–1297. doi:10.1016/S0003-9993(96)90195-1
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Smith, C. E., Nyland, J., Caudill, P., Brosky, J., & Caborn, D. N. M. (2008). Dynamic trunk stabilization: A conceptual back injury prevention program for volleyball athletes. The Journal of Orthopaedic and Sports Physical Therapy, 38, 703–720. doi:10.2519/jospt.2008.2814 Vera-Garcia, F. J. (2003). Adaptaciones neuromusculares tras un programa de entrenamiento abdominal dinámico y otro estático [Neuromuscular adaptations after dynamic and static abdominal training program] (Doctoral dissertation). Universitat de Valencia, Valencia, Spain. Vera-Garcia, F. J., Flores-Parodi, B., Elvira, J. L. L., & Sarti, M. A. (2008). Influence of trunk curl-up speed on muscular recruitment. Journal of Strength and Conditioning Research, 22, 684–690. doi:10.1519/JSC.0b013e31816d5578
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European Journal of Sport Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejs20
Effect of movement speed on trunk and hip exercise performance a
a
a
b
Jose L. L. Elvira , David Barbado , Belen Flores-Parodi , Janice M. Moreside & Francisco J. a
Vera-Garcia a
Sports Research Centre, Miguel Hernandez University of Elche, Alicante, Spain
b
School of Physiotherapy, Dalhousie University, Halifax, Canada Published online: 22 Nov 2013.
To cite this article: Jose L. L. Elvira, David Barbado, Belen Flores-Parodi, Janice M. Moreside & Francisco J. Vera-Garcia (2014) Effect of movement speed on trunk and hip exercise performance, European Journal of Sport Science, 14:6, 547-555, DOI: 10.1080/17461391.2013.860483 To link to this article: http://dx.doi.org/10.1080/17461391.2013.860483
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European Journal of Sport Science, 2014 Vol. 14, No. 6, 547–555, http://dx.doi.org/10.1080/17461391.2013.860483
ORIGINAL ARTICLE
Effect of movement speed on trunk and hip exercise performance
JOSE L. L. ELVIRA1, DAVID BARBADO1, BELEN FLORES-PARODI1, JANICE M. MORESIDE2, & FRANCISCO J. VERA-GARCIA1 Sports Research Centre, Miguel Hernandez University of Elche, Alicante, Spain, 2School of Physiotherapy, Dalhousie University, Halifax, Canada
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Abstract The influence of speed on trunk exercise technique is poorly understood. The aim of this study was to analyse the effect of movement speed on the kinematics and kinetics of curl-up, sit-up and leg raising/lowering exercises. Seventeen healthy, recreationally trained individuals (13 females and 4 males) volunteered to participate in this study. Four different exercise cadences were analysed: 1 repetition/4 s, 1 repetition/2 s, 1 repetition/1.5 s and 1 repetition/1 s. The exercises were executed on a force plate and recorded by three cameras to conduct a 3D photogrammetric analysis. The cephalo-caudal displacement of the centre of pressure and range of motion (ROM) of six joints describing the trunk and hip movements were measured. As sit-up and curl-up speed increased, hip and knee ROM increased. Dorsal-lumbar and upper trunk ROM increased with speed in the curl-up. Faster cadence in the sit-up exercise had minimal effect on trunk ROM: only the upper trunk ROM decreased significantly. In the leg raising/lowering exercise there was a decrease in the pelvic tilt and hip ROM, and increased knee flexion ROM. During higher speed exercises, participants modified their technique to maintain the cadence. Thus, professionals would do well to monitor and control participants’ technique during high-speed exercises to maintain performance specificity. Results also suggest division of speed into two cadence categories, to be used as a reference for prescribing exercise speed based on preferred outcome goals. Keywords: Biomechanics, 3D analysis, kinetics, core training
Introduction Core exercises are widely used in clinical, recreational and sport settings to achieve various goals. Examples comprise improved spine stability for back injury prevention or rehabilitation (Borghuis, Hof, & Lemmink, 2008; McGill, 2002; Smith, Nyland, Caudill, Brosky, & Caborn, 2008), increased muscle strength and power in professional athletes (McGill, 2004) and developed muscular endurance in high school physical education students (Vera-Garcia, 2003). Research on core exercises has mainly focused on assessing exercise effectiveness and safety by analysing trunk muscle recruitment (Monfort-Pañego, Vera-Garcia, Sanchez-Zuriaga, & Sarti-Martinez, 2009) and spine loads (Axler & McGill, 1997; Kavcic, Grenier, & McGill, 2004), respectively. Consequently, a large number of biomechanical studies have evaluated the effect of various factors of trunk exercise performance on muscle response and/or
spinal loading: spine and hip flexion, (Axler & McGill, 1997; Juker, McGill, Kropf, & Steffen, 1998), trunk rotation and bending (Axler & McGill, 1997; Juker et al., 1998; McGill, 1991; Vera-Garcia, Moreside, & McGill, 2011), supported segments (Andersson, Nilsson, Ma, & Thorstensson, 1997; Guimaraes, Vaz, De Campos, & Marantes, 1991), arm and hand position (Alexander, 1985; Knudson, 1999), knee and hip position, (Andersson et al., 1997; Axler & McGill, 1997; García-Vaquero, Moreside, Brontons-Gil, Peco-Gonzalez, & Vera-Garcia, 2012), movement of upper vs. lower body, (Lehman & McGill, 2001; Sarti, Monfort, Fuster, & Villaplana, 1996; Vera-Garcia, Moreside, & McGill, 2010; VeraGarcia et al., 2011), the use of equipment (Marshall & Murphy, 2005; Moreside, Vera-Garcia, & McGill, 2007; Sánchez-zuriaga, Vera-Garcia, Moreside, & McGill, 2009; Vera-Garcia, Grenier, & McGill, 2000), movement speed (Godfrey, Kindig, & Windell, 1977;
Correspondence: J. L. L. Elvira, Sports Research Centre, Universidad Miguel Hernández de Elche, Avda. de la Universidad, S/N.03202 Elche, Alicante, Spain. E-mail: [email protected] © 2013 European College of Sport Science
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Vera-Garcia, 2003; Vera-Garcia, Flores-Parodi, Elvira, & Sarti, 2008), etc. Speed of movement, controlled by the movement cadence, is one of the variables that can be easily modified to adjust the intensity of the exercises. Vera-Garcia et al. (2008) reported an increase in the activation and co-activation of the trunk muscles when increasing the speed of curl-up or crunch exercises. Similarly, Godfrey et al. (1977) found higher durations of rectus abdominis and external oblique activation during fast sit-up exercises compared to slow sit-ups. However, scientific evaluation of the influence of movement speed on trunk exercise technique is lacking. An increase in the speed of movement implies an increase in segmental angular momentum, and potentially modified range of motion (ROM) of the principal joints (Bruijn, Meyns, Jonkers, Kaat, & Duysens, 2011). In addition, it is expected that a threshold cadence exists, after which the movement is no longer controlled by the agonist muscles only, but requires associated plyometric contractions from both the agonist and antagonist muscles. This rapid alternating between segmental acceleration and deceleration may result in altered movement patterns and muscle lengths compared to a slower cadence. In turn, muscles may be working in different force–length relationships than those expected, thus resulting in modified exercise effects. The aim of this hypothesis-driven study was to analyse the effect of movement speed on the kinematics and kinetics of three commonly used trunk and hip strengthening exercises: curl-up, sit-up and double leg raising/lowering. Specifically, we were interested in identifying variations in exercise technique resulting from speed increases, which may subsequently impact training results.
Methods Subjects An a-priori power analysis was conducted to estimate the sample size. GPower software (GPower 3.1.7, Kiel University, Germany) estimated a sample size of 14 subjects (effect size with partial eta squared, g2p ¼ 0.25; significance level = 0.05; required power = 0.80; correlation among repeated measures = 0.30). Seventeen healthy participants, 13 females and 4 males (mean age = 23.6, s = 4.4 years; height = 166.3, s = 6.5 cm; mass = 61.0, s = 8.4 kg) were recruited from the university setting. All participants were healthy, without current hip or back pain or past pathology in these regions. Each participant was recreationally trained, defined as participating in noncompetitive physical activities such as jogging,
swimming, cycling and resistance exercises at least three times per week, for a minimum of 30 min per session. Similarly, each reported participation in core training exercises (i.e., common trunk and hip strengthening and endurance exercises) at least one session per week. Written informed consent was obtained from each participant prior to testing. The experimental procedures used in this study were in accordance with the Declaration of Helsinki and were approved by the University Office for Research Ethics. Procedures Participants were instructed in the execution of the three exercises (curl-up, sit-up and leg raising/lowering). For the curl-up and the sit-up performance, they were required to lay on a force platform (600 × 370 mm, Dinascan 600M, IBV, Valencia, Spain) in a supine position with arms crossed in front of the chest, and shoulders flexed and internally rotated 90° (Figure 1a and b). A 0.6 cm thick fitness mat with the same dimensions as the force platform was affixed atop the platform to increase the participants’ comfort and prevent slipping from the initial position. In the curl-up, participants were to raise their head and shoulders off the platform, but not lift further than the inferior scapular borders (Figure 1a). The emphasis was in curling the upper thoracic spine forwards in the sagittal plane. In the sit-up, participants were instructed to raise their upper body to a point where they could touch their knees with their elbows, while their ankles were secured by the investigator (Figure 1b). The leg raising/lowering exercise required each supine participant to raise both lower limbs simultaneously until the feet touched a bar, indicating the vertical position, while maintaining knee extension (Figure 1c). The participants stabilised their upper body position by grasping the ankles of the investigator (Figure 1c). One complete repetition of each exercise included both raising and lowering of the body segment. Ten repetitions of each were performed sequentially. Three cadences were tested for each exercise: 1 repetition/4 s (C4), 1 repetition/2 s (C2) and 1 repetition/1.5 s (C1.5). The curl-ups were also performed at 1 repetition/1 s (C1), but this cadence was found to be too fast for the other two exercises. A metronome was used to pace the cadence. Participants were instructed to carry out all exercises with a constant and fluid motion. The order of the exercises was randomised, resting 3 min between cadences and 5 min between exercises. Speed conditions were ordered from lowest to highest for each exercise, as had previously been determined as the optimal order for participants to adapt to betweentrial cadence changes.
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Effect of movement speed on exercise performance
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Figure 1. Initial and final positions of each of the three exercises being tested. One complete repetition included a return to the start position. Subjects were instructed to perform at a constant speed and fluid motion, while cadence was paced with a metronome.
Exercises were performed such that the region from the participant’s shoulders to pelvis was resting on the force plate, with the sagittal plane of their body aligned with the long axis of the force plate. On average, 85% of their total weight was resting on the force plate in the initial position. After each exercise and cadence, participants were repositioned on the force plate. Ground reaction forces were recorded at 500 Hz, and centre of pressure (COP) of the body lying on the force plate in the cephalo-caudal direction was calculated. Three digital cameras (Canon XM1, Sony DCRTRV33 and Sony SSC-DC338), recording at 50 Hz, were placed at 0°, 45° and 90° from the sagittal plane. The reference frame used was a prism of 2 × 1 × 1 m. Reflective markers were placed on the following anatomical landmarks on the right side of the body: lateral malleolus, lateral femoral condyle, greater trochanter, anterior superior iliac spine, mid-
point between the anterior superior iliac spine and posterior superior iliac spine, mid-point of the lowest rib, inferior lateral angle of the scapula and acromion (Figure 2a). Markers were automatically digitised and reconstructed using standard photogrammetry algorithms (Kwon 3D software: Visol Inc., Korea). A six segment model was used. The following angles pro‐ jected in the sagittal plane were calculated (Figure 2b): . . .
Upper trunk with the horizontal (UTH): angle between acromion-scapula segment compared to the horizontal. Dorsal flexion (DF): angle between scapulalowest rib segment compared to the acromion-scapula segment. Dorsal-lumbar flexion (DLF): angle between scapula-lowest rib segment and lowest ribmid-point between the anterior superior iliac spine segment.
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Figure 2. A model of eight points and six segments was used. (a) Anatomical markers: LM: lateral malleolus; LFC: lateral femoral condyle; T: trochanter; ASIS: anterior superior iliac spine; MPSIS: mid-point between the ASIS and posterior superior iliac spine; LR: lower rib; S: inferior angle of the scapula; AC: acromion. (b) Measured angles: UTH: upper trunk with the horizontal; DF: dorsal flexion; DLF: dorsallumbar flexion; PT: pelvic tilt; H: hip; K: knee.
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Pelvic tilt (PT): angle between lowest rib-midpoint between the anterior superior iliac spine segment and mid-point between the anterior superior iliac spine-anterior superior iliac spine segment. Hip (H): angle between lateral femoral condyle-greater trochanter segment compared to mid-point between the anterior superior iliac spine-anterior superior iliac spine segment. Knee (K): angle between lateral malleoluslateral femoral condyle segment and lateral femoral condyle-greater trochanter segment.
In the leg raising/lowering exercise, the upper trunk angles UTH and DF were not reported as their movement was negligible. Despite the fact that 10 repetitions were performed, only 5 repetitions (usually 4 through 8) were used for analysis; the first repetitions were discarded to ensure the participants were in time with the cadence, and the last repetitions removed to diminish the possibility of fatigue influencing the movement pattern. For each of the six angles, total ROM and COP displacement were averaged over the five trials, then the mean calculated across all participants.
Statistical analyses To ensure that sex did not influence the results, we conducted an exploratory statistical comparison between males and females: a mixed ANOVA for each exercise and variable, with speed as the withinsubject factor and sex the between-subject factor. Results indicate that sex does not significantly affect speed (P > 0.05) in any of the variables and exercises. In order to evaluate the possibility of the trunk slipping on the platform while performing the exercises, a repeated measures ANOVA was used to compare the minimum and maximum displacement of the COP (initial and final COP position, respectively) between repetitions for each exercise and speed. In addition, the intraclass correlation coefficient (twoway random effects model) was calculated to assess the relative reliability between repetitions for the minimum, maximum and total displacement of the COP, and the standard error of measurement to assess the absolute reliability between repetitions for the total COP displacement. The standard error of measurement was not performed for minimum and maximum COP displacement because they are arbitrary values that depend on the participant’s dimensions. Intraclass correlation coefficients for
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Effect of movement speed on exercise performance maximum, minimum and total COP displacement ranged between 0.85 and 0.96 across exercises and speeds. Standard errors of measurement for total COP displacement ranged between 4 and 8%. Finally, repeated measures ANOVA did not find statistical differences for the initial and final COP position between repetitions in any trial. Overall, these results demonstrate the reliability of the measurements, indicating that the trunk did not slip on the force platform while preforming the exercises at different speeds. To evaluate the effect of movement speed on the kinematics and kinetics of curl-up, sit-up and leg raising/lowering exercises, a repeated measures ANOVA with cadence as a factor was performed for each exercise. Bonferroni post hoc tests with a significance level chosen at P < 0.05 were carried out to allow within-exercise cadence comparisons. No between-exercise comparisons were made because the mass and radius of gyration were not comparable between exercises, despite similar cadences. Partial eta squared (g2p ) was also calculated as a measure of effect size and proportion of the overall variance that is attributable to the factor. Values of effect size ≥0.64 were considered strong, around 0.25 were considered moderate and ≤ 0.04 were considered small (Ferguson, 2009). All analyses utilised the SPSS package version 20.0 (IBM SPSS Inc., Chicago, IL, USA). Results The averages for the COP displacement and ROM of the aforementioned angles are shown in Table I. See Figure 3 for a pictorial representation of the changes in the initial and final position, comparing slowest and fastest cadence. Results indicate that, in all three exercises, a faster cadence elicited greater displacement of the COP (P < 0.001). In the curl-up exercise, increasing speed resulted in significantly greater ROM of all angles except DF. The largest changes were seen in the DLF and UTH ROM, which increased an average of 8.4° and 7.6°, respectively. During the sit-up, the hip and knee ROM increased an average of 5.0° and 3.4°, respectively, with increasing speed, whereas UTH decreased an average of 8.4°. As speed increased in the leg raising/lowering exercise, mean PT and hip flexion ROM decreased (2.9 and 2.7°, respectively), while average knee ROM increased a substantial 8.5°. Discussion A common problem in sports training and exercise is the ability to control the intensity of the activity. Given that training effects are specific to
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performance velocity (Kanehisa & Miyashita, 1983), some athletes require high-speed exercises and plyometrics to improve performance (McGill, 2004). One of the training variables that can easily be manipulated to modulate the intensity of trunk exercises is the speed of movement (Vera-Garcia et al., 2008), which can be adjusted by the cadence of the exercise. In the present study, the effects of movement speed on three conventional trunk and hip strengthening exercises were analysed. It was anticipated that increases in angular momentum due to the higher speed would cause an increase in trunk motion. This is supported by the significant increase in the COP displacement in all exercises (Table I). However, the effect of velocity on angular ROM differed between exercises. It should be noted that this study was conducted on healthy, young volunteers, and may not reflect movement strategies that would be adopted in different populations, such as those with low back pain, different age groups or varying athletic abilities. Curl-up In the curl-up, flexion is focused in the mid-thoracic region, as measured by DF. Increasing the cadence did not modify DF ROM, therefore the focus of the exercise appears to remain the same. However, the UTH angle increased with each faster cadence (P < 0.001, g2p ¼ 0.493), thus demonstrating an increase in the overall upper trunk movement relative to the ground. This can be explained by the increase in DLF (P < 0.001, g2p ¼ 0.555), which appears to be a side effect of increasing the angular momentum due to the increase in the angular velocity. This exercise had no tactile end goal at the end of the upwards phase: unlike the sit-up or leg raising/lowering, participants were not aiming to reach their knees or a bar. Consequently, with increasing speed, there may have been less specificity as to the end point of the exercise, resulting in greater flexion throughout the spine, and possibly lifting the lower scapular borders off the platform (Figure 3a). Repetitive lumbar flexion is known to be potentially injurious to the intervertebral discs (Callaghan & McGill, 2001; Nachemson, 1966), thus, this change in technique associated with higher speeds should be closely monitored. Increasing curl-up speed was also associated with corresponding increases in COP displace‐ ment (P < 0.001, g2p ¼ 0.804) and PT (P < 0.001, g2p ¼ 0.493), considered to be strong and moderate effect sizes, respectively. The increase in PT ROM may be interpreted as a consequence of activating the trunk extensor muscles while relaxing the flexors at the end of the upwards movement to facilitate rapid deceleration and downwards acceleration of trunk
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Table I. Average angular range of motion (degrees) and centre of pressure displacement (cm) at each cadence (C4: 1 repetition/4 s; C2: 1 repetition/2 s; C1.5: 1 repetition/1.5 s; C1: 1 repetition/1 s)
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Variables
C4
Curl-up COP 11.6 UTH 40.2 DF 31.2 DLF 18.7 PT 8.8 Hip 3.7 Knee 1.1 Sit-up COP 33.4 UTH 107.8 DF 23.2 DLF 23.6 PT 33.9 Hip 37.6 Knee 12.8 Leg raising/lowering COP 21.6 DLF 10.9 PT 31.7 Hip 58.3 Knee 11.4
C2
C1.5
C1
Partial eta squared
< 0.001 < 0.001 0.288 < 0.001 < 0.001 0.028 < 0.001
0.804 0.493 0.075 0.555 0.493 0.174 0.716
± ± ± ± ± ± ±
3.5 7.2 6.5 6.7 3.4 2.6 1.0
14.8 42.0 30.8 21.6 10.3 3.7 1.7
± ± ± ± ± ± ±
3.8A 5.3 6.8 7.0A 3.0A 1.8 1.3
23.1 45.3 32.1 23.9 11.4 4.0 2.8
± ± ± ± ± ± ±
4.1AB 7.0AB 7.8 6.0A 4.8AB 2.5 1.9AB
23.0 47.8 32.3 27.1 14.1 5.6 4.2
± ± ± ± ± ± ±
4.0 9.5 7.0 8.1 7.2 6.8 3.7
35.8 106.8 23.2 24.9 31.3 39.9 15.0
± ± ± ± ± ± ±
6.7 10.4 8.9 8.0 7.0 7.7A 3.5A
40.0 99.4 19.4 23.3 30.4 42.6 16.2
± ± ± ± ± ± ±
7.4AB 12.4AB 9.1 8.7 9.2 8.3AB 3.0A
– – – – – – –
< 0.001 0.001 0.067 0.443 0.053 < 0.001 < 0.001
0.408 0.372 0.155 0.045 0.167 0.476 0.489
± ± ± ± ±
2.9 5.1 8.0 8.6 5.6
26.4 11.1 31.2 58.5 14.7
± ± ± ± ±
3.6A 4.8 7.6 9.6 7.1A
35.1 12.9 28.8 55.6 19.9
± ± ± ± ±
3.7AB 5.4 8.6AB 8.0AB 12.4AB
– – – – –
< 0.001 0.065 0.006 0.001 0.004
0.916 0.174 0.275 0.361 0.374
± ± ± ± ± ± ±
4.1ABC 7.6AB 7.2 6.0ABC 4.6ABC 3.2ABC 1.9ABC
p-value
Notes: ASignificantly different from C4; BSignificantly different from C2; CSignificantly different from C1.5; (significance value of P < 0.05). COP: cephalo-caudal centre of pressure displacement; UTH: angle of upper trunk with the horizontal; DF: dorsal flexion angle; DLF: dorso-lumbar angle; PT: pelvic tilt; Hip: hip angle; Knee: knee angle (see document and Figure 2 for more complete descriptions).
motion at the higher cadences. Nevertheless, further research is necessary to confirm this hypothesis. Increasing cadence also resulted in greater hip and knee ROM (P = 0.028, g2p ¼ 0.174, and P < 0.001, g2p ¼ 0.716, respectively), thus a different muscular activation pattern may have occurred. These changes could be due to increased angular momentum with speed, making it more difficult to slow down the trunk motion, and thus resulting in increased COP displacement and greater hip and knee ROM. It is likely that greater increases in hip and knee ROM might have occurred on a more slippery surface, thus, using some type of non-slip surface is recommended when exercising at high speeds.
Sit-up In the sit-up exercise, the main joint involved in the trunk sagittal displacement is the hip. With increasing cadence, hip ROM also increased significantly with a moderate effect size (P < 0.001, g2p ¼ 0.476). At the faster cadences, it was observed that many participants raised their pelvis while moving backwards at the end of the downwards phase (see Figure 3b), possibly in an attempt to provide extra impulse to raise the trunk in the next concentric contraction phase. This manoeuvre implied a slight hip extension (Figure 3b) that explains the ROM increases in the hip angle.
Increased hip ROM occurred without associated changes in DF or DLF, but with a significant reduction in UTH ROM in the fastest cadence. Thus, faster cadences did not affect the temporal strategy used to raise the trunk from the force plate: that of upper trunk flexion followed by a hip flexion (Cordo et al., 2003). Nevertheless, the reduction in scope of the UTH ROM may be attributed to an attempt to reduce the angular displacement of the trunk and head in the deceleration phases at the end of each upwards and downwards movement as participants struggled to maintain the higher cadences.
Leg raising/lowering In the leg raising/lowering exercise, the hip is again the main focus of movement. There were no significant changes in hip ROM between the C4 and C2 cadences, but at the fastest cadence (C1.5), hip ROM was significantly reduced. This was in conjunction with an increase in knee ROM, thus increased knee flexion, despite instructions to maintain knee extension. This may be an adaptation of the exercise technique to reduce the radius of gyration and thus the angular momentum, facilitating the ability to maintain the highest cadence. Even with significant changes in ROM, the effect size in
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Effect of movement speed on exercise performance
Figure 3. Stick figures of a representative subject performing the three analysed exercises. The initial and final positions of one repetition are shown. Solid lines represent the slowest cadence (C4); dashed lines represent the fastest cadence (C1 for curl-up exercise and C1.5 for sit-up and leg raising/lowering exercises).
both angles tended to be moderate (hip g2p ¼ 0.361 and knee g2p ¼ 0.374). Interestingly, speed increases in the leg raising/ lowering exercise caused a significant reduction in the total PT ROM (P = 0.006, g2p ¼ 0.275). This reduction occurred despite the fact that this exercise is the one in which the COP displacement was more affected by speed and had the highest effect size (P < 0.001, g2p ¼ 0.916). Although this reduction could be interpreted as a result of an increase in the trunk muscle co-activation, the reduction could have been due to other factors such as the aforementioned simultaneous reduction in hip ROM and increased knee ROM. There was also a
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nonsignificant trend for increasing cadence to result in more DLF, inferring that motion was occurring higher up the spine. Whether this motion represents increased lumbar extension or flexion, repetitive plyometric sagittal spine motion should not be recommended for patients with motor control deficits or low back disorders, nor those who are untrained or unfit, due to the possibility of injury to the intervertebral discs (Aultman, Scannell, & McGill, 2005; Callaghan & McGill, 2001; McGill, 2004; Parkinson, Beach, & Callaghan, 2004). For the three exercises in general, rationale would indicate that while lower cadences require only the flexor muscles to be continuously active, both concentrically (upwards) and eccentrically (downwards), the higher cadences require the alternating activity of both flexor and extensor muscles to be able to maintain the cadence (plyometric contraction, slowing down eccentrically and accelerating concentrically). This has been shown previously for the curl-up exercise (Vera-Garcia et al., 2008), and similar muscle responses could be expected for the sit-up and leg raising/lowering exercises. Based on the number of statistical differences found, it appears that C4 and C2 fit into the ‘lower cadence’ category, while C1.5 and C1 could be considered ‘higher cadence’ due to the ensuing changes in motion patterns. This cadence division could potentially be considered as a reference for prescribing exercise speed, based on preferred outcome goals. Lower cadences may be more appropriate for a clinical rehabilitation setting as patients may be especially sensitive to spine loading magnitudes. In that trunk dynamics have a significant impact on spinal loads (Davis & Marras, 2000) there may be a need to control exercise speed in clinical settings to reduce risk of injury. Conversely, higher cadences may be recommended in a sport environment in which participants are seeking more power and plyometric contractions to challenge the neuromuscular system in a way that is similar to that of competition (Vera-Garcia et al., 2008). These results indicate that performance technique during three specific trunk exercises changed with the speed of movement. Most of the changes seem to be due to the participants’ difficulty in keeping up with higher cadences (especially C1.5 and C1). The higher speeds require fast plyometric contractions, which entail altered motor control and specific motion patterns. Thus, it appears that as cadence increases, the focus changes from one of technique to that of maintaining a specific speed, resulting in altered kinetics and kinematics. In addition, not only do these three exercises have different goals but also these can be further subdivided by cadence, to increase exercise outcome specificity. As a reference, up to a 2-s cadence can be considered as ‘low’ and
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faster cadences as ‘high’. While the former may be more appropriate for a rehabilitation setting, the higher speeds may be more relevant in a sports environment. However, exercise cadence is a variable that requires close monitoring and correction, as technique alterations will likely ensue. Professionals utilising trunk and hip strengthening exercises should bear this in mind when designing exercise programmes. Acknowledgements
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