The effect of knee and foot position on the electromyographical activity of the superficial quadriceps.

Isometric quadriceps exercises are used early in knee rehabilitation. Varying knee or foot position is hypothesized to selectively activate specific quadriceps muscles. This study examined the activities of the vastus medialis oblique, vastus lateralis, and rectus femoris during isometric contractions at 90 degrees, 150 degrees, and 175 degrees knee angles with internally rotated, neutral, and externally rotated foot positions. Subjects performed three perceived maximal isometric contractions at each knee angle/foot position while electromyographic activity (EMG) was collected. Statistical analysis consisted of a three-way repeated measures multiple analysis of variance, with post hoc analysis as was appropriate. Although no significant differences were detected among foot positions for the rectus femoris at 90 degrees, this knee angle produced significantly greater EMG activity for the neutral position compared with 150 degrees or 175 degrees. The 90 degrees angle was also superior to 175 degrees for the externally rotated position. The results for both the vastus medialis and vastus lateralis were similar, with the 90 degrees angle producing greater EMG activity than 175 degrees in the externally rotated position. In addition, the neutral position produced significantly more activity than the internally rotated position at 90 degrees. At 150 degrees, the neutral position was superior to the externally rotated position. Finally, at the 175 degrees knee angle, the highest level of EMG activity was with the foot internally rotated. Considering the combination of effects for EMG activity across all muscles tested, the 90 degrees knee angle with a neutral foot position may provide the most effective condition for rehabilitation of all muscles tested.(ABSTRACT TRUNCATED AT 250 WORDS)