The effects of an isometric knee extension with hip adduction (KEWHA) exercise on selective VMO muscle strengthening.

We investigated the effects of four weeks of training using a knee extension with hip adduction (KEWHA) exercise in asymptomatic participants. In addition, we compared different methods of electromyographic (EMG) onset-time detection. Eighteen participants who achieved earlier activation of the vastus lateralis (VL) muscle compared to that of the vastus medialis obliquus (VMO) muscle performed the isometric KEWHA exercise in the sitting position for four weeks. A 15° hip adduction was added to the existing knee extension in the KEWHA exercise. EMG onset times were detected using a computer-analyzed system and evaluated using two methods in which the thresholds for activity onset were set at two and three standard deviations (SDs) of the mean baseline activity. No significant difference in the EMG onset-time for the VMO muscle was observed compared to that of the VL muscle between the pre- and post-tests (p>0.05) when data at 2SDs of the mean baseline activity were analyzed. However, a significant difference in the onset times for the VMO muscle and VL muscle was found between the pre- and post-tests (p<0.05) when data at 3SDs of the mean baseline activity were analyzed. In addition, less variation was observed in data analyzed at 3SDs compared to that of the data at 2SDs. The normalized VMO:VL muscle ratio was not significantly different between the pre- and post-tests. These findings show that the KEWHA exercise may decrease the difference between the onset times of VMO and VL muscles. In addition, we suggest that task-specific EMG onset-time detection methods are required to minimize variations in the data obtained during the recording of muscle activation.