Quadriceps concentric EMC activity is greater than eccentric EMG activity during the lateral step-up exercise

Purpose: To analyze vastus medialis obliquus (VMO) and vastus lateralis (VL) muscle activity during the concentric and eccentric phases of a lateral step-up exercise. Design: Repeated-measures. Dependent variable: the integrated electromyogram measured as a percentage of the maximal voluntary isometric contraction of the VMO and VL muscles. Independent variable: muscle contraction with 2 levels (concentric and eccentric). Subjects: Twenty-three volunteers with no previous history of knee surgery or anterior knee pain. Methods:Surface electrodes were positioned over the VMO and VL, and electromyographic data were collected during the exercise. Results: The 2 muscle phases of contraction were different when both dependent variables were considered simultaneously (F-2,F-17 = 33.2, P < .001). Concentric contractions produced greater muscle activity for VL (P < .05) and VMO (P < .05). Conclusions: Because concentric contractions produce greater activity than eccentric contractions do during the lateral step-up exercise, they provide a stronger stimulus for muscle activation, which might result in greater muscle strength gains.