Abdominal strengthening exercises are often recommended as both a prophylactic and a treatment for low back pain. The requirements placed upon the low back muscles themselves during the execution of abdominal strengthening exercises, however, have not been previously reported. The purpose of this study was to compare levels of myoelectric activity in the low back muscles as well as in selected abdominal and hip flexor muscles across eight variations of the sit-up. Twenty-seven male subjects performed three repetitions each of three book-lying sit-ups (with 65, 90 and 105 degrees of flexion at the knee), and of the long-lying sit-up (with 0 degrees of knee flexion). All four sit-up variations were done both with and without manual support of the feet. Myoelectric activity in the rectus abdominis, external oblique, rectus femoris, and the L3 level of sacrospinalis was monitored during the trials.
Lack of feet support resulted in greater (p < 0.05) iEMG values at the two abdominal sites and in less recorded iEMG in the rectus femoris. Myoelectric activity in the lumbar sacrospinalis was signifcantly greater with the feet unsupported. At both the external oblique and L3 sites, EMG activity increased with increasing angle of flexion at the knee. Of the sit-up variations examined, the book-lying sit-ups performed without feet support appear to be the most taxing to both the abdominal muscles and the low back muscles.
(C) 1990 National Strength and Conditioning Association