Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study.

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 silver-silver 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 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.