An Electromyographic lnvestigation of the Quadriceps Muscles During the Performance of Multiple Angle Isometric Exercises

In clinical practice, physical therapists often employ various forms of quadriceps strengthening exercise to target the vastus medialis oblique (VMO) and the vastus medialis (VM) component of the quadriceps muscle. These strengthening exercises usually consist of multiple angle isometrics (MAI) performed throughout the range from 0°to 120°knee ｆｌexion. There is no evidence that any of these exercises is able to selectively target the individual component of the quadriceps muscle group. The aim of this study is to provide electromyographic evidence of quadriceps muscle selectivity during the performance of MAI exercise. Eleven subjects (7 females and 4 males) participated in this study. The mean age of subjects was 19.36+1.43 years, and the mean weight was 53.00+5.16 kg. Ag/AgCI surface electrodes were attached to the subjects' thigh, at sites corresponding to the vastus lateralis (VL), VM, VMO, and the rectus femoris (RF). Subjects were asked to perform isometric knee extension excrcises at 7 positions corresponding to 20°,３０°,45°,60°,75°,90°,and 110°knee flexion. Each exercise was performed for 3 repetitions : with a 5-seconds hold period, and a rest interval of 30 seconds. The order of exercise was randomized. The raw EMG data was processed using a Butterworth band pass filter (10 to 240 Hz), rectified and integrated (IEMG). The IEMG data was analyzed using a paired T test. The level of significance was set at 0.05. In general, the results showed that the mean IEMG of the RF, VMO and VL increased as knee flexion angle increased while the mean IEMG of the VMO remained relatively unchanged throughout the tested range. The VM/VL ratio decreased, while the VMO/VL ratio increased as knee flexion angle increased. These results demonstrate that it is possible to selectively exercise the different components of the quadriceps muscles using multiple angle isometric exercises between 20°and 110°knee flexion.