- Email: [email protected]
Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study
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MODEL
Journal of Bodywork & Movement Therapies (2016) xx, 1e6
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/jbmt
RELIABILITY STUDY
Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study Javid Mostamand, MSc PT, PhD, Associate Professor of Physiotherapy a,*, ¨ Hudson, PhD, MCSP c Dan L. Bader, DSc b, Zoe a Musculoskeletal Research Centre, Faculty of Rehabilitation Sciences, Isfahan University of Medical Sciences, PO Box: 164, 8174673461, Isfahan, Iran b Faculty of Health Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK c Centre for Sports and Exercise Medicine, Barts and the London Queen Mary’s School of Medicine and Dentistry, Mann Ward, Mile End Hospital, Bancroft Road, London, E1 4DG, UK
Received 14 December 2015; received in revised form 14 March 2016; accepted 31 March 2016
KEYWORDS VMO/VL reliability test; Leg predomination; Single leg squatting
Summary Introduction: Although measuring vasti muscle activity may reveal whether pain relief is associated with altering this parameter during functional activities in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring VMO/VL amplitude. The aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO/VL amplitude measurement during single leg squatting in healthy subjects. Methods: Using an electromyography (EMG) unit, the ratio amplitudes of VMO and VL muscles of ten healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from two silveresilver surface electrodes placed over the muscle bellies of the VMO and VL. This procedure was performed on the both right and left legs, during three separate single leg squats from a neutral position to a depth of approximately 30 of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week’s interval. The amplitude of VMO and VL were then calculated using root mean square (RMS). Results: There was no significant difference between the VMO/VL amplitude mean values of paired test of right (mean, SD of 0.85, 0.10) and left knees (mean, SD of 0.82, 0.10) (p > 0.05). The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of VMO/VL amplitude measurements on both knees. The ICC (intra class correlation coefficient) values during within and between
* Corresponding author. Tel.: þ98 (0) 313 6693089; fax: þ98 (0)313 6687270. E-mail addresses: [email protected] (J. Mostamand), [email protected] (D.L. Bader), [email protected] (Z. Hudson). http://dx.doi.org/10.1016/j.jbmt.2016.04.012 1360-8592/ª 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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J. Mostamand et al. sessions tests showed the high reliability of these measurements on both knees. Conclusion: The high reliability of VMO/VL amplitude measurements on both dominant and non-dominant legs of healthy subjects suggests that the VMO/VL amplitude measurement would not be influenced by the leg predomination during single leg squatting. ª 2016 Elsevier Ltd. All rights reserved.
Introduction Vastus medialis (VM) muscle has been implicated as the primary medial stabilizer of the patella. Assuming this role, it has been proposed that this muscle, especially its oblique part that is, vastus medialis obliquus (VMO) is capable of counterbalancing the lateral pull of the larger vastus lateralis (VL) to ensure patellar stability within the trochlear groove (McConnell, 2002). Different functional activities resulting in greater knee flexion angle such as stair stepping or squatting may be inhibited in subjects with patellofemoral pain syndrome (PFPS). It has been proposed that balanced activation of the VMO and VL is disrupted in subjects with PFPS (McConnell, 1986) and such condition may alter normal patellar tracking explaining the cause of pain in these subjects. Conservative treatment of patellofemoral pain has therefore focused on restoring normal patellar tracking by improving dynamic stability (McConnell, 2002) through quadriceps retraining (especially VMO) or passive modalities to reduce the symptoms of subjects. Additionally, electromyographic (EMG) studies proved that during varying types of static and dynamic forceful activities such as stair stepping task, jumping and squatting, the activation of VMO and VL are relatively balanced in normal subjects (Lange et al., 1996; Karst and Willett, 1997). It is hypothesized that any pain relief in PFPS subjects following quadriceps retraining may be related to balancing vasti activities. Measuring vasti muscle activity may therefore reveal whether the pain relief is associated with altering this parameter during functional activities. Previous study revealed moderate to relatively high intratester reliability of within and between session tests (IntraClass Coefficient Correlation Z ICC values) of VMO/ VL amplitude measurements in healthy subjects during single leg squatting (Mostamand et al., 2013). The relatively high value of within session ICC (0.84e0.90) was also reported by Sheehy et al. (1998) for the peak amplitude of VMO and VL activity in the eccentric and concentric phases of stair walking. Although the reliability test for VMO and VL activity measurement during single leg squatting and stair stepping task was shown to be relatively high, it might be necessary to find whether the inherent properties of both right and left legs influences the reliability of these measurements. There are some evidences revealing different level of EMG activation in various groups of muscles in the right or left leg dominant players. In a study conducted by Mondal et al. (2014), it was observed that in the right leg dominant soccer players and left leg
dominant players, EMG activity of quadriceps and calf muscles were significantly higher in their dominant leg. In the hamstring muscle, while the EMG activity of left leg dominant players was significantly higher in their left leg, the EMG activity of hamstrings in the right dominant players was not significantly high compared to contralateral leg during the similar activity. Although this study focused on athletes, differences between level of muscle activities in both dominant and non-dominant legs may influence the reliability of muscle activity measurements during different functional activities and different subjects. According to the literature, the current authors could not find any data to show if leg predomination affects amplitude measuring of vasti muscles during functional activities. Therefore, the aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO/VL amplitude measurement during single leg squatting in healthy subjects. Future studies on the VMO/VL amplitude values would be more reliable in the symptomatics, if the results show that leg predomination does not affect the reliability testing of the VMO/VL amplitude measurement during single leg squatting.
Methods Subjects The present study was approved by the East London and City Research Ethics Committee before recruiting subjects. Written informed consent was provided by each subject. The study was designed to examine the VMO/VL amplitude values and the reliability of outcome measurement (VMO/VL amplitude) during single leg squatting on both the dominant and non-dominant leg. For this, ten healthy volunteers with right dominant legs (6 men and 4 women) with age (mean, SD) of 27, 6 y, weight of 70, 10 kg and height of 172, 7 cm were recruited into the study. To determine dominant legs, all volunteers were questioned “which leg do you use when you kick a ball?”. These volunteers had no traumatic, inflammatory or infectious pathology in their lower extremity and spinal column. Subjects with a history of knee surgery, dislocation or subluxation of their patellofemoral joints were excluded from the study. Additionally, age of more than 40 years was one of the exclusion criteria to ensure subjects had no signs of secondary osteoarthritis (Crossley et al., 2002). The subjects, selected from students studying at Queen Mary University, London based on a general call to perform this project. These well-conditioned students were also
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? required to perform five single leg squats, repeatedly for each leg. Eight out of eighteen subjects who did not meet the inclusion criteria were excluded from the present study.
Instrumentation Two silveresilver surface electrodes (MedCaT.B.V, The Netherlands) were placed over the muscle bellies of the VMO and VL with an interelectrode distance of 24 mm, as illustrated in Fig. 1. Before electrode placement, the skin was shaved and washed with water to minimise the electrical impedance. The electrode for the VMO was placed over the muscle belly approximately 4 cm superior to and 3 cm medial to the superomedial patella border and oriented 55 to the vertical. The electrode for the VL was placed 10 cm superior and 6e8 cm lateral to the superior border of the patella, and oriented 15 to the vertical (Gilleard et al., 1998). The reference electrode was placed over the tibial tubercle. Using an electromyography (EMG) unit (Biovision, D61273, Germany) the ratio amplitudes of VMO and VL muscles were measured. The EMG data were preamplified 10 times with a sampling rate of 1000 Hz. The root mean square (RMS) amplitude of VMO and VL for a representative 1000 ms period (low pass filtered at 50 Hz) were then calculated (McGregor et al., 2005).
Test procedure Before starting the main tests, all subjects were trained to perform a single leg squat to the required degrees of knee flexion, using verbal feedbacks (zero to approximately 30 of knee flexion). To control any trunk forward flexion or deviation, they were asked to keep their feet in full contact with the floor during single leg squatting, while verbal feedback was used to encourage subjects to hold their trunks in a vertical position. Each subject was then instructed to stand on one leg and to keep the contralateral leg off the floor. The first leg to be tested for each subject and for each test session was selected using randomized numbers, even and odd, selected from a container. Subjects were requested to execute three separate single leg
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squats in each session from a neutral position (zero degree of knee flexion) to a depth of approximately 30 of knee flexion, while maintaining heel contact with the floor. Each squat was limited to about 3 s which was monitored by a stop watch. The test was repeated on a different day with a minimum interval of one week. Thus each subject performed six separate squats, incorporating two sets of three repetitions for each leg in each session. As a whole, 12 squats were performed by each subject during two separate test sessions.
Data analysis All data were analyzed (SPSS-version 16) during the eccentric phase of squatting at 30 of knee flexion. This angle was selected as it was thought to be most appropriate for comparative purposes with biomechanical variables associated with subjects with PFPS (Ernest et al., 1999). The ShapiroWilk test was applied to all data sets (2 test sessions) of VMO/VL amplitude measurements on both knees to test for normality. All data sets were found to be normally distributed and hence parametric statistics were used. Using paired-sample T test, the mean differences of VMO/VL amplitude measurements between right and left knees with 95% CI were calculated. From the mean and standard deviation of each data set, the Coefficient Of Variation (CV) (Portney and Watkins, 2000) was calculated to describe the variability of the VMO/VL amplitude measurements, both within (R1, R2 & R3) and between (R1 & R2) session tests on both knees. Random two-way intra class correlation coefficients for a single measure (ICC type 2,1) (Portney and Watkins, 2000) were also used to examine whether the corresponding values of VMO/VL amplitude on both knees exhibited significant correlation, both within and between sessions. In addition, an alternative statistics was used to establish random error of each paired measurements at the 5% level namely, the within session standard error of measurement (SEM) values of VMO/VL amplitude for the two test sessions on both knees (Portney and Watkins, 2000).
Results Table 1 reveals the mean (SD) values of right and left knee VMO and VL muscle activity during eccentric phase of squatting, calculated at 30 of knee joint flexion. According
Table 1 Summarized EMG data of study on 10 healthy subjects during eccentric phase of single leg squatting at 30 degrees of knee flexion on the both right and left knees.
Figure 1 Electrode placement over the VMO and VL muscles of the right knee.
Right knee Left knee
VMO amplitude (mV)
VL amplitude (mV)
VMO/VL amplitude
0.81 0.19 0.76 0.17
0.95 0.14 0.93 0.18
0.85 0.10 0.82 0.10
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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4 to the results, there was no significant difference between the VMO/VL amplitude mean values of paired test of right and left knees (p > 0.05).
Coefficient of variation (CV) values Values of the CV which were obtained from the VMO/VL amplitude measurements (between session repetitions) at 30 of knee flexion during eccentric phase of single leg squatting on both knees (Appendix 1) indicated that the CV varied between 1.54% and 19.27% for the right and 1.42% and 14.11% for the left knees of ten healthy subjects denoted S1e10. The within session CV values of VMO/VL amplitude measurements also varied between 0.94% and 20.00% for the right and 2.22% and 10.76% for the left knees (Appendix 2). As shown in both Appendices 1 and 2, the majority of variability measurements were less than 10% for the between session and within session tests, respectively. This value has previously been reported to indicate low scattered variability (Von Eisenhart-Rothe et al., 2004) and thus both reproducibility and repeatability in this measurement was considered adequate for normal subjects.
Intra class correlation coefficient (ICC) values An analysis of the data using the between session ICC revealed relatively high intratester reliability of the single measures (0.83, 95% CI 0.64e0.92) for the VMO/VL amplitude measurements of the right knees. According to the data, there was also the same intratester reliability of the single measures (0.82, 95% CI 0.63e0.91) for the same measurements on the left knees. The within session ICC revealed high intratester reliability of the single measures for the VMO/VL amplitude measurements on both right (0.91, 95% CI 0.89e0.98) and left knees (0.89, 95% CI 0.86e0.94).
Standard error of measurement (SEM) values The SEM values of VMO/VL amplitude measurements on both knees were between 0.02 and 0.03 for three repetitions. These values showed that there was no significant difference for the SEM of each repetition of tests on both knees (p > 0.05). Indeed, these values demonstrated that the differences between repeated measures were not clinically relevant on both knees.
J. Mostamand et al. found to be statistically different (p > 0.05). The ratio values for both right (0.85 0.10) and left knees (0.82 0.10) were less than a unit for healthy subjects, which were consistent with the studies performed by Tang et al. (2001) and Mostamand et al. (2013). The reliability of VMO/VL amplitude measurement during different functional activities in healthy subjects had previously been reported (Sheehy et al., 1998; Mostamand et al., 2013). The relatively high value of within session ICC (0.84e0.90) was reported by Sheehy et al. (1998) for the peak amplitude of VMO and VL activity in the eccentric and concentric phases of stair walking. The current authors (Mostamand et al., 2013) also showed that the reliability of VMO/VL amplitude measurements was high during single leg squatting, regardless of inherent effects of legs on these measurements. The similarity of ICC values in these studies reveal that the repeatability and reproducibility tests of vasti amplitude were acceptable enough to conduct the study during single leg squatting and stair stepping tasks. As the reliability of VMO/VL amplitude measurement during functional activities in healthy subjects had previously been reported (Sheehy et al., 1998; Mostamand et al., 2013), the current study was designed to compare the reliability of VMO/VL amplitude measurements during single leg squatting in both dominant and non-dominant legs. Although the VMO/VL amplitude values was not statistically different in the both left and right dominant legs in the present study, the CV values revealed that both repeatability and reproducibility of measurements were adequate and similar on both legs, indicating no influence of leg predomination on variability of measurements during single leg squatting. In addition, it was found that leg predomination could not affect the reliability of VMO/VL amplitude measurements, both within and between sessions during similar activity, as measuring this variable revealed high intratester reliability in both dominant and non-dominant legs. The relatively low values of within and between session SEM during the present study, revealed that the random error of measurements were low in both dominant and nondominant legs, showing high precision of the VMO/VL amplitude measurements during the similar activity. Although the SEM is based on the characteristics of the normal curve and therefore a meaningful estimate can usually be made with a large sample of scores (Portney and Watkins, 2000), this statistic was used to express how far the standard deviation of errors reflects the reliability of the response, revealing precision of the measurements (Taylor, 1999).
Discussion The null hypothesis tested in the current study involved no differences in the ratio of the amplitudes of VMO and VL muscles for both knees of healthy subjects. The results confirmed this null hypothesis during the eccentric phase of single leg squatting at 30 degrees of knee flexion in both knees. The mean values related to the right knees were only slightly greater than the left values (Table 1). However, the related differences in these mean values were not
Conclusion The high reliability of VMO/VL amplitude measurements on both dominant and non-dominant legs of healthy subjects suggests that the VMO/VL amplitude measurement would not be influenced by the leg predomination during single leg squatting.
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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Does leg predomination affect the measurement of vasti muscle activity during single leg squatting?
Limitations It is important to note that both kinematic and kinetic data would be influenced by alteration in the centre of body mass. The researcher was careful in initial training and subsequent verbal feedback, so that each subject performed the single leg squatting protocol without any rising of the heel or trunk deviation. Nonetheless, alteration in centre of body mass might still have occurred in the form of anterior flexion of the trunk in healthy subjects, performing single leg squatting.
Conflict of interest statement We confirm that the authors have no conflict of interests regarding this paper.
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Obliquus Z VMO, Vastus Lateralis Z VL, S Z Subject, R Z repetition).
Within session repetitions
CV of the VMO/VL amplitude (%) (R knees)
CV of the VMO/VL amplitude (%) (L knees)
S1 (R1eR2eR3) S2 (R1eR2eR3) S3 (R1eR2eR3) S4 (R1eR2eR3) S5 (R1eR2eR3) S6 (R1eR2eR3) S7 (R1eR2eR3) S8 (R1eR2eR3) S9 (R1eR2eR3) S10 (R1eR2eR3)
1.70 3.77 3.55 2.75 0.94 11.83 2.30 10.47 20.00 2.30
6.40 3.28 5.83 6.50 2.22 3.73 10.76 10.20 7.72 3.93
Acknowledgement This article was financially supported by Isfahan University of Medical Sciences and Ministry of Health and Medical Education of Islamic Republic of Iran.
Appendix 1. Coefficient of variation (CV) of the VMO/VL amplitude measurement (between session repetitions) during eccentric phase of single leg squatting at 30 degrees of the knee flexion on both knees (Vastus Medialis Obliquus Z VMO, Vastus Lateralis Z VL, S Z Subject, R Z repetition).
Between session repetitions
CV of the VMO/VL amplitude for the right knees (%)
CV of the VMO/VL amplitude for the left knees (%)
S1 (R1eR2) S2 (R1eR2) S3 (R1eR2) S4 (R1eR2) S5 (R1eR2) S6 (R1eR2) S7 (R1eR2) S8 (R1eR2) S9 (R1eR2) S10 (R1eR2)
7.27 6.91 6.67 1.54 2.36 19.27 3.40 2.71 10.44 3.40
8.47 9.89 6.62 7.06 1.42 3.78 14.11 7.40 8.85 4.15
Appendix 2. Coefficient of variation (CV) of the VMO/VL amplitude measurement (within session repetitions), during eccentric phase of single leg squatting at 30 degrees of the knee flexion on both knees (Vastus Medialis
References Crossley, K., Bennell, K., Green, S., Cowan, S., McConnell, J., 2002. Physical therapy for patellofemoral pain: a randomized, double blinded, placebo-controlled trial. Am. J. Sports Med. 30 (6), 857e865. Ernest, G.P., Kawaguchi, J., Saliba, E., 1999. Effect of patellar taping on knee kinetic of patients with patellofemoral pain syndrome. J. Orthop. Sports Phys. Ther. 29 (11), 661e667. Gilleard, W., McConnell, J., parsons, D., 1998. The effect of patellar taping on the onset of vastus medialis obliqus and vastus lateralis muscle activity in persons with patellofemoral pain. Phys. Ther. 78, 25e31. Karst, G.M., Willett, G.M., 1997. Reflex response times of vastus medialis oblique and vastus lateralis in normal subjects and in subjects with patellofemoral pain. Letter to editor J. Orthop. Sports Phys. Ther. 26 (2), 108e109. Lange, G.W., Hintermeister, R.A., Schlegal, T., et al., 1996. Electromyographic and kinematic analysis of graded treadmill walking and implications for knee rehabilitation. J. Orthop. Sports Phys. Ther. 23 (5), 294e301. McConnell, J., 1986. The management of chondromalacia patellae: a long-term solution. Aust. J. Physiother. 32 (4), 215e223. McConnell, J., 2002. The physical therapist’s approach to patellofemoral disorders. Clin. Sports Med. 21, 363e387. McGregor, K., Gerlach, S., Mellor, R., et al., 2005. Cutaneous stimulation from patella tape causes a differential increase in vasti muscle activity in people with patellofemoral pain. J. Orthop. Res. 23, 351e358. Mondal, S., Chhangte, Z., Guyan, A., et al., 2014. Dominant and non-dominant leg muscle electrical activity of soccer players: a preliminary study. Int. Refereed J. Eng. Sci. 3 (4), 65e69. Mostamand, J., Bader, D.L., Hudson, Z., 2013. Reliability testing of vasti activity measurements in taped and untapped patellofemoral conditions during single leg squatting in healthy subjects: a pilot study. J. Bodyw. Mov. Ther. 17, 271e277. Portney, L.G., Watkins, M.P., 2000. Foundations of Clinical Research e Applications to Practice, second ed. Prentice Hall. Sheehy, P., Burdett, R.G., Irrgang, J.J., et al., 1998. An electromyographic study of vastus medialis oblique and vastus lateralis
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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6 activity while ascending and descending steps. J. Orthop. Sports Phys. Ther. 27 (9), 423e429. Tang, S.F., Chen, C.K., Hsu, R., et al., 2001. Vastus medialis obliqus and vastus lateralis activity in open and closed kinetic chain exercises in patients with patellofemoral pain syndrome: an electromyographic study. Archives Phys. Med. Rehabil. 82, 1441e1445.
J. Mostamand et al. Taylor, J.R., 1999. An Introduction to Error Analysis: the Study of Uncertainties in Physical Measurements. University Science Books, Sausalito, California. Von Eisenhart-Rothe, R., Siebert, M., Bringmann, C., et al., 2004. A new in vivo technique for determination of 3D kinematics and contact areas of the patello-femoral and tibio-femoral joint. J. Biomech. 37 (6), 927e934.
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
MODEL
Journal of Bodywork & Movement Therapies (2016) xx, 1e6
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/jbmt
RELIABILITY STUDY
Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study Javid Mostamand, MSc PT, PhD, Associate Professor of Physiotherapy a,*, ¨ Hudson, PhD, MCSP c Dan L. Bader, DSc b, Zoe a Musculoskeletal Research Centre, Faculty of Rehabilitation Sciences, Isfahan University of Medical Sciences, PO Box: 164, 8174673461, Isfahan, Iran b Faculty of Health Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK c Centre for Sports and Exercise Medicine, Barts and the London Queen Mary’s School of Medicine and Dentistry, Mann Ward, Mile End Hospital, Bancroft Road, London, E1 4DG, UK
Received 14 December 2015; received in revised form 14 March 2016; accepted 31 March 2016
KEYWORDS VMO/VL reliability test; Leg predomination; Single leg squatting
Summary Introduction: Although measuring vasti muscle activity may reveal whether pain relief is associated with altering this parameter during functional activities in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring VMO/VL amplitude. The aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO/VL amplitude measurement during single leg squatting in healthy subjects. Methods: Using an electromyography (EMG) unit, the ratio amplitudes of VMO and VL muscles of ten healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from two silveresilver surface electrodes placed over the muscle bellies of the VMO and VL. This procedure was performed on the both right and left legs, during three separate single leg squats from a neutral position to a depth of approximately 30 of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week’s interval. The amplitude of VMO and VL were then calculated using root mean square (RMS). Results: There was no significant difference between the VMO/VL amplitude mean values of paired test of right (mean, SD of 0.85, 0.10) and left knees (mean, SD of 0.82, 0.10) (p > 0.05). The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of VMO/VL amplitude measurements on both knees. The ICC (intra class correlation coefficient) values during within and between
* Corresponding author. Tel.: þ98 (0) 313 6693089; fax: þ98 (0)313 6687270. E-mail addresses: [email protected] (J. Mostamand), [email protected] (D.L. Bader), [email protected] (Z. Hudson). http://dx.doi.org/10.1016/j.jbmt.2016.04.012 1360-8592/ª 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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J. Mostamand et al. sessions tests showed the high reliability of these measurements on both knees. Conclusion: The high reliability of VMO/VL amplitude measurements on both dominant and non-dominant legs of healthy subjects suggests that the VMO/VL amplitude measurement would not be influenced by the leg predomination during single leg squatting. ª 2016 Elsevier Ltd. All rights reserved.
Introduction Vastus medialis (VM) muscle has been implicated as the primary medial stabilizer of the patella. Assuming this role, it has been proposed that this muscle, especially its oblique part that is, vastus medialis obliquus (VMO) is capable of counterbalancing the lateral pull of the larger vastus lateralis (VL) to ensure patellar stability within the trochlear groove (McConnell, 2002). Different functional activities resulting in greater knee flexion angle such as stair stepping or squatting may be inhibited in subjects with patellofemoral pain syndrome (PFPS). It has been proposed that balanced activation of the VMO and VL is disrupted in subjects with PFPS (McConnell, 1986) and such condition may alter normal patellar tracking explaining the cause of pain in these subjects. Conservative treatment of patellofemoral pain has therefore focused on restoring normal patellar tracking by improving dynamic stability (McConnell, 2002) through quadriceps retraining (especially VMO) or passive modalities to reduce the symptoms of subjects. Additionally, electromyographic (EMG) studies proved that during varying types of static and dynamic forceful activities such as stair stepping task, jumping and squatting, the activation of VMO and VL are relatively balanced in normal subjects (Lange et al., 1996; Karst and Willett, 1997). It is hypothesized that any pain relief in PFPS subjects following quadriceps retraining may be related to balancing vasti activities. Measuring vasti muscle activity may therefore reveal whether the pain relief is associated with altering this parameter during functional activities. Previous study revealed moderate to relatively high intratester reliability of within and between session tests (IntraClass Coefficient Correlation Z ICC values) of VMO/ VL amplitude measurements in healthy subjects during single leg squatting (Mostamand et al., 2013). The relatively high value of within session ICC (0.84e0.90) was also reported by Sheehy et al. (1998) for the peak amplitude of VMO and VL activity in the eccentric and concentric phases of stair walking. Although the reliability test for VMO and VL activity measurement during single leg squatting and stair stepping task was shown to be relatively high, it might be necessary to find whether the inherent properties of both right and left legs influences the reliability of these measurements. There are some evidences revealing different level of EMG activation in various groups of muscles in the right or left leg dominant players. In a study conducted by Mondal et al. (2014), it was observed that in the right leg dominant soccer players and left leg
dominant players, EMG activity of quadriceps and calf muscles were significantly higher in their dominant leg. In the hamstring muscle, while the EMG activity of left leg dominant players was significantly higher in their left leg, the EMG activity of hamstrings in the right dominant players was not significantly high compared to contralateral leg during the similar activity. Although this study focused on athletes, differences between level of muscle activities in both dominant and non-dominant legs may influence the reliability of muscle activity measurements during different functional activities and different subjects. According to the literature, the current authors could not find any data to show if leg predomination affects amplitude measuring of vasti muscles during functional activities. Therefore, the aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO/VL amplitude measurement during single leg squatting in healthy subjects. Future studies on the VMO/VL amplitude values would be more reliable in the symptomatics, if the results show that leg predomination does not affect the reliability testing of the VMO/VL amplitude measurement during single leg squatting.
Methods Subjects The present study was approved by the East London and City Research Ethics Committee before recruiting subjects. Written informed consent was provided by each subject. The study was designed to examine the VMO/VL amplitude values and the reliability of outcome measurement (VMO/VL amplitude) during single leg squatting on both the dominant and non-dominant leg. For this, ten healthy volunteers with right dominant legs (6 men and 4 women) with age (mean, SD) of 27, 6 y, weight of 70, 10 kg and height of 172, 7 cm were recruited into the study. To determine dominant legs, all volunteers were questioned “which leg do you use when you kick a ball?”. These volunteers had no traumatic, inflammatory or infectious pathology in their lower extremity and spinal column. Subjects with a history of knee surgery, dislocation or subluxation of their patellofemoral joints were excluded from the study. Additionally, age of more than 40 years was one of the exclusion criteria to ensure subjects had no signs of secondary osteoarthritis (Crossley et al., 2002). The subjects, selected from students studying at Queen Mary University, London based on a general call to perform this project. These well-conditioned students were also
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? required to perform five single leg squats, repeatedly for each leg. Eight out of eighteen subjects who did not meet the inclusion criteria were excluded from the present study.
Instrumentation Two silveresilver surface electrodes (MedCaT.B.V, The Netherlands) were placed over the muscle bellies of the VMO and VL with an interelectrode distance of 24 mm, as illustrated in Fig. 1. Before electrode placement, the skin was shaved and washed with water to minimise the electrical impedance. The electrode for the VMO was placed over the muscle belly approximately 4 cm superior to and 3 cm medial to the superomedial patella border and oriented 55 to the vertical. The electrode for the VL was placed 10 cm superior and 6e8 cm lateral to the superior border of the patella, and oriented 15 to the vertical (Gilleard et al., 1998). The reference electrode was placed over the tibial tubercle. Using an electromyography (EMG) unit (Biovision, D61273, Germany) the ratio amplitudes of VMO and VL muscles were measured. The EMG data were preamplified 10 times with a sampling rate of 1000 Hz. The root mean square (RMS) amplitude of VMO and VL for a representative 1000 ms period (low pass filtered at 50 Hz) were then calculated (McGregor et al., 2005).
Test procedure Before starting the main tests, all subjects were trained to perform a single leg squat to the required degrees of knee flexion, using verbal feedbacks (zero to approximately 30 of knee flexion). To control any trunk forward flexion or deviation, they were asked to keep their feet in full contact with the floor during single leg squatting, while verbal feedback was used to encourage subjects to hold their trunks in a vertical position. Each subject was then instructed to stand on one leg and to keep the contralateral leg off the floor. The first leg to be tested for each subject and for each test session was selected using randomized numbers, even and odd, selected from a container. Subjects were requested to execute three separate single leg
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squats in each session from a neutral position (zero degree of knee flexion) to a depth of approximately 30 of knee flexion, while maintaining heel contact with the floor. Each squat was limited to about 3 s which was monitored by a stop watch. The test was repeated on a different day with a minimum interval of one week. Thus each subject performed six separate squats, incorporating two sets of three repetitions for each leg in each session. As a whole, 12 squats were performed by each subject during two separate test sessions.
Data analysis All data were analyzed (SPSS-version 16) during the eccentric phase of squatting at 30 of knee flexion. This angle was selected as it was thought to be most appropriate for comparative purposes with biomechanical variables associated with subjects with PFPS (Ernest et al., 1999). The ShapiroWilk test was applied to all data sets (2 test sessions) of VMO/VL amplitude measurements on both knees to test for normality. All data sets were found to be normally distributed and hence parametric statistics were used. Using paired-sample T test, the mean differences of VMO/VL amplitude measurements between right and left knees with 95% CI were calculated. From the mean and standard deviation of each data set, the Coefficient Of Variation (CV) (Portney and Watkins, 2000) was calculated to describe the variability of the VMO/VL amplitude measurements, both within (R1, R2 & R3) and between (R1 & R2) session tests on both knees. Random two-way intra class correlation coefficients for a single measure (ICC type 2,1) (Portney and Watkins, 2000) were also used to examine whether the corresponding values of VMO/VL amplitude on both knees exhibited significant correlation, both within and between sessions. In addition, an alternative statistics was used to establish random error of each paired measurements at the 5% level namely, the within session standard error of measurement (SEM) values of VMO/VL amplitude for the two test sessions on both knees (Portney and Watkins, 2000).
Results Table 1 reveals the mean (SD) values of right and left knee VMO and VL muscle activity during eccentric phase of squatting, calculated at 30 of knee joint flexion. According
Table 1 Summarized EMG data of study on 10 healthy subjects during eccentric phase of single leg squatting at 30 degrees of knee flexion on the both right and left knees.
Figure 1 Electrode placement over the VMO and VL muscles of the right knee.
Right knee Left knee
VMO amplitude (mV)
VL amplitude (mV)
VMO/VL amplitude
0.81 0.19 0.76 0.17
0.95 0.14 0.93 0.18
0.85 0.10 0.82 0.10
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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4 to the results, there was no significant difference between the VMO/VL amplitude mean values of paired test of right and left knees (p > 0.05).
Coefficient of variation (CV) values Values of the CV which were obtained from the VMO/VL amplitude measurements (between session repetitions) at 30 of knee flexion during eccentric phase of single leg squatting on both knees (Appendix 1) indicated that the CV varied between 1.54% and 19.27% for the right and 1.42% and 14.11% for the left knees of ten healthy subjects denoted S1e10. The within session CV values of VMO/VL amplitude measurements also varied between 0.94% and 20.00% for the right and 2.22% and 10.76% for the left knees (Appendix 2). As shown in both Appendices 1 and 2, the majority of variability measurements were less than 10% for the between session and within session tests, respectively. This value has previously been reported to indicate low scattered variability (Von Eisenhart-Rothe et al., 2004) and thus both reproducibility and repeatability in this measurement was considered adequate for normal subjects.
Intra class correlation coefficient (ICC) values An analysis of the data using the between session ICC revealed relatively high intratester reliability of the single measures (0.83, 95% CI 0.64e0.92) for the VMO/VL amplitude measurements of the right knees. According to the data, there was also the same intratester reliability of the single measures (0.82, 95% CI 0.63e0.91) for the same measurements on the left knees. The within session ICC revealed high intratester reliability of the single measures for the VMO/VL amplitude measurements on both right (0.91, 95% CI 0.89e0.98) and left knees (0.89, 95% CI 0.86e0.94).
Standard error of measurement (SEM) values The SEM values of VMO/VL amplitude measurements on both knees were between 0.02 and 0.03 for three repetitions. These values showed that there was no significant difference for the SEM of each repetition of tests on both knees (p > 0.05). Indeed, these values demonstrated that the differences between repeated measures were not clinically relevant on both knees.
J. Mostamand et al. found to be statistically different (p > 0.05). The ratio values for both right (0.85 0.10) and left knees (0.82 0.10) were less than a unit for healthy subjects, which were consistent with the studies performed by Tang et al. (2001) and Mostamand et al. (2013). The reliability of VMO/VL amplitude measurement during different functional activities in healthy subjects had previously been reported (Sheehy et al., 1998; Mostamand et al., 2013). The relatively high value of within session ICC (0.84e0.90) was reported by Sheehy et al. (1998) for the peak amplitude of VMO and VL activity in the eccentric and concentric phases of stair walking. The current authors (Mostamand et al., 2013) also showed that the reliability of VMO/VL amplitude measurements was high during single leg squatting, regardless of inherent effects of legs on these measurements. The similarity of ICC values in these studies reveal that the repeatability and reproducibility tests of vasti amplitude were acceptable enough to conduct the study during single leg squatting and stair stepping tasks. As the reliability of VMO/VL amplitude measurement during functional activities in healthy subjects had previously been reported (Sheehy et al., 1998; Mostamand et al., 2013), the current study was designed to compare the reliability of VMO/VL amplitude measurements during single leg squatting in both dominant and non-dominant legs. Although the VMO/VL amplitude values was not statistically different in the both left and right dominant legs in the present study, the CV values revealed that both repeatability and reproducibility of measurements were adequate and similar on both legs, indicating no influence of leg predomination on variability of measurements during single leg squatting. In addition, it was found that leg predomination could not affect the reliability of VMO/VL amplitude measurements, both within and between sessions during similar activity, as measuring this variable revealed high intratester reliability in both dominant and non-dominant legs. The relatively low values of within and between session SEM during the present study, revealed that the random error of measurements were low in both dominant and nondominant legs, showing high precision of the VMO/VL amplitude measurements during the similar activity. Although the SEM is based on the characteristics of the normal curve and therefore a meaningful estimate can usually be made with a large sample of scores (Portney and Watkins, 2000), this statistic was used to express how far the standard deviation of errors reflects the reliability of the response, revealing precision of the measurements (Taylor, 1999).
Discussion The null hypothesis tested in the current study involved no differences in the ratio of the amplitudes of VMO and VL muscles for both knees of healthy subjects. The results confirmed this null hypothesis during the eccentric phase of single leg squatting at 30 degrees of knee flexion in both knees. The mean values related to the right knees were only slightly greater than the left values (Table 1). However, the related differences in these mean values were not
Conclusion The high reliability of VMO/VL amplitude measurements on both dominant and non-dominant legs of healthy subjects suggests that the VMO/VL amplitude measurement would not be influenced by the leg predomination during single leg squatting.
Please cite this article in press as: Mostamand, J., et al., Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study, Journal of Bodywork & Movement Therapies (2016), http://dx.doi.org/10.1016/ j.jbmt.2016.04.012
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Does leg predomination affect the measurement of vasti muscle activity during single leg squatting?
Limitations It is important to note that both kinematic and kinetic data would be influenced by alteration in the centre of body mass. The researcher was careful in initial training and subsequent verbal feedback, so that each subject performed the single leg squatting protocol without any rising of the heel or trunk deviation. Nonetheless, alteration in centre of body mass might still have occurred in the form of anterior flexion of the trunk in healthy subjects, performing single leg squatting.
Conflict of interest statement We confirm that the authors have no conflict of interests regarding this paper.
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Obliquus Z VMO, Vastus Lateralis Z VL, S Z Subject, R Z repetition).
Within session repetitions
CV of the VMO/VL amplitude (%) (R knees)
CV of the VMO/VL amplitude (%) (L knees)
S1 (R1eR2eR3) S2 (R1eR2eR3) S3 (R1eR2eR3) S4 (R1eR2eR3) S5 (R1eR2eR3) S6 (R1eR2eR3) S7 (R1eR2eR3) S8 (R1eR2eR3) S9 (R1eR2eR3) S10 (R1eR2eR3)
1.70 3.77 3.55 2.75 0.94 11.83 2.30 10.47 20.00 2.30
6.40 3.28 5.83 6.50 2.22 3.73 10.76 10.20 7.72 3.93
Acknowledgement This article was financially supported by Isfahan University of Medical Sciences and Ministry of Health and Medical Education of Islamic Republic of Iran.
Appendix 1. Coefficient of variation (CV) of the VMO/VL amplitude measurement (between session repetitions) during eccentric phase of single leg squatting at 30 degrees of the knee flexion on both knees (Vastus Medialis Obliquus Z VMO, Vastus Lateralis Z VL, S Z Subject, R Z repetition).
Between session repetitions
CV of the VMO/VL amplitude for the right knees (%)
CV of the VMO/VL amplitude for the left knees (%)
S1 (R1eR2) S2 (R1eR2) S3 (R1eR2) S4 (R1eR2) S5 (R1eR2) S6 (R1eR2) S7 (R1eR2) S8 (R1eR2) S9 (R1eR2) S10 (R1eR2)
7.27 6.91 6.67 1.54 2.36 19.27 3.40 2.71 10.44 3.40
8.47 9.89 6.62 7.06 1.42 3.78 14.11 7.40 8.85 4.15
Appendix 2. Coefficient of variation (CV) of the VMO/VL amplitude measurement (within session repetitions), during eccentric phase of single leg squatting at 30 degrees of the knee flexion on both knees (Vastus Medialis
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