Purpose : The purpose of this study was to determine the effects of hip adduction using a ball on the activation of the vastus medialis oblique (VMO) and the vastus lateralis (VL) during dynamic semisquat exercises. Methods : Twenty seven participants performed three repetitions of a double-leg semisquat and squeeze semisquat (semisquat with hip adduction using a ball) at $60^{circ}$ knee flexion. The activation of the VMO and the VL was recorded at dominant leg during both semisquat exercises using surface electromyography (MP 100). EMG data were normalized to the maximal voluntary isometric contraction (MVIC) of the quadriceps produced during seated, isometric knee extension. Results : Results of paired t-test analyses revealed that there were no differences between activity of the VMO and the VL in both double-leg semisquat and squeeze semisquat. The activity of the VMO was significantly increased in squeeze semisquat whereas there was no difference in activity of the VL between double-leg semisquat and squeeze semisquat. Conclusion : Combining hip adduction using a ball with semisquat at $60^{circ}$ knee flexion preferentially increases the activity of the VMO. We can conclude that semisquat at $60^{circ}$ knee flexion with hip adduction using a ball selectively recruits the VMO. Rehabilitation for quadricep imbalance should consider these findings when selecting exercises which could preferentially activate the VMO.