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To examine the effect of leg rotation on the vastus medialis oblique/vastus lateralis (VMO/VL) electromyogram (EMG) activity ratio during two closed chain knee extension exercises prescribed for patellofemoral pain syndrome (PFPS).
Subjects performed step-up/step-down (SUSD) and modified wall-slide (MWS), exercises with the leg neutral (SUSD/N, MWS/N), internally rotated (SUSD/I, MWS/I), and externally rotated (SUSD/E, MWS/E), respectively, for determination of root mean square EMG.
Six athletically active females symptomatic for PFPS and nine athletically active asymptomatic female control subjects.
The EMG activity of the VMO and the VL was collected while the subjects performed the exercises. Root mean square EMG was determined and then normalized to the subjects' maximal voluntary isometric contractions for calculation and analysis of the VMO/VL activity ratio.
Leg rotation had no effect on the VMO/VL activity ratio for the symptomatic group. The SUSD/E produced a lower VMO/VL activity ratio compared with the SUSD/N (p < .01) and the SUSD/I (p < .01) in the control group. Similarly, the VMO/VL activity ratio for the MWS/E was lower than for the MWS/I (p < 0.01).
These results suggest that external rotation of the leg may affect VMO/VL activity ratio during closed chain knee extension exercises in individuals without PFPS but not in individuals symptomatic for PFPS.