The purpose of this study is to try to quantify the differences in isometric and isotonic exercises of vastus medialis and vastus lateralis of quadriceps, knee extension, and straight leg raising exercises.

In 20 healthy Korean male adults, EMG(rectified mean amplitude) was analyzed quantitatively in vastus medialis vastus lateralis and rectus femoris in various conditions.

The followings are summarized results of the study;

1) The quantitative EMG values in knee extension exercises are higher than in straight leg raising exercises(p<0.001).

2) The quantitative EMG values in isometric exercises are higher than in isotonic exercises. (p<0.05-p<0.001)

3) The activity of the vastus medialis was not limited to the last 15°~20° of extension, but rather took place during all of the knee extension.

4) a. Vastus lateralis and vastus medialis are generally active than rectus femoris.

b. Vastus medialis is more active than vastus lateralis in 5 exercises out of 8(10% isotonic knee extension, 10% istonic straight leg raising, 30% isotonic knee extension, 10% isotonic straight leg raising, 30% isotonic knee extension, 10% isometric knee extension, 30% isometric straight leg raising) and vastus lateralis is more active in remainder.(30% isotonic straight leg raising, 10% isometric knee extension, 30% isometric straight leg raising)

5) As was expected, the quantitative EMG values in 30% repetition maximum weight are higher than in 10% repetition maximum weight.