The purpose of this study was to compare the EMG activity of Vastus Medialis Oblique (VMO) and Vastus Lateralis (VL) muscles in the single- joint knee extension (KE) and the multi- joint leg press (LP). Subjects performed two maximal voluntary isometric contractions (MVC) and LP and KE actions subsequently performed at individual load، equal 80% of MVC in each exercise modality. 15 healthy men، (mean age 31.93 ± 7.08 yrs، mean height 176.6 ± 5.93 cm، mean weight 72± 12.62 kg) with no previous of knee pain، trauma، surgery، or other joint disease participated in the study.The EMG signal of VMO and VL muscles was recorded bilaterally during both exercises. Results showed no significant difference between LP and KE. However when EMG activity of VMO and VL muscles were compared whit each other، a significant difference was found (p ≤ 0.05)، and in both action the activity of VMO was more than VL. Regardless of the exercise model this suggests the increased demand of involvement may not be equally shared among muscles possessing different anatomical origin and insertion. Motor control plays an important role in rehabilitation in general and patellofemoral joint problems in particular
