Intra-abdominal pressure and trunk muscle activity during lifting. III. Effect of abdominal muscle training in chronic low-back patients.

Isometric training of the abdominal muscles is often recommended in programs of primary or secondary prevention for low-back pain. In this study 20 male workers with 2-18 years' history (average 5 1/2 years) of low-back pain without sciatica went through intense isometric abdominal muscle training for 5 weeks. Before and after training the subjects had trunk flexion and extension strength tests and a series of standardized lifts. The intraabdominal pressure (IAP) and the EMG activity of the oblique abdominal muscles, and of the erector spinae muscle were recorded. It was found that: the strength of the abdominal muscles increased; the increased strength was correlated to an improved recruitment of motor units in the oblique abdominal muscles; the EMG activity of the oblique abdominal muscles when lifting decreased after training, i.e. the acquired ability to recruit more motor units was not made use of; the IAP at lifting was generally not affected. A better knowledge of the mechanisms responsible for the IAP in different situations is needed to support advice on training or other prevention.