OBLIQUE ABDOMINAL MUSCLE-ACTIVITY IN STANDING AND IN SITTING ON HARD AND SOFT SEATS

The activity of the oblique abdominal muscles was investigated with th e trunk in unconstrained, symmetrical and static postures. Electromyog raphic recordings in six healthy subjects revealed that in all subject s the activity of both the internal and the external obliques is signi ficantly higher in unconstrained standing than in supine posture. Acti vity of the internal oblique was higher than that of the external obli que abdominal. The sacrospinal, gluteus maximus and biceps femoris mus cles showed practically no activity in unconstrained erect posture. Du ring unconstrained sitting both oblique abdominals are active. In most subjects the activity of the oblique abdominals was significantly sma ller when sitting on a soft car seat than when sitting on an office ch air with a hard seat. The possibility is discussed that contraction of the oblique abdominals in unconstrained standing and sitting may help in stabilizing the basis of the spine and particularly the sacroiliac joints. During standing and sitting the oblique abdominal muscles app arently have a significant role in sustaining gravity loads. Relevance Back pain and pelvic pain are often experienced in prolonged standing and sitting postures. In these postures the oblique abdominals are sh own to be active. The present study gains clinical significance by the studies showing relatively small oblique abdominal muscle strength in patients with low back pain. A soft seat may be helpful in treatment and prevention, because it substitutes oblique abdominal muscle activi ty.