Electromyographic study of duration of muscle activity in sit-up variations.

The external oblique, rectus abdominis, and rectus femoris muscles of 17 college women were studied electromyographically in 8 sit-up variations to determine the best variation for maximizing abdominal muscle activity and minimizing hip flexor activity. Integrated action potentials and movement phases of each variation were recorded simultaneously. The duration of muscle activity within the movement phases was analyzed. The variables of hook-lying/long-lying, feet supported/feet unsupported, and slow/fast speed of performance were examined. The hook-lying unsupported slow and fast variations were best for maximizing abdominal muscle duration of activity and for minimizing rectus femoris muscle duration of activity. Greatest duration of activity for all muscles occurred in the long-lying supported fast variation. Supporting the feet in both hook and long-lying fast variations was more effective for increasing activity duration of all muscles than the slow supported variations. Speed of performance seemed to be as important as support of the feet or leg position in increasing duration of muscle activity.