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 (F2,7= 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.
