Effects of the mechanical load on forward bending motion of the trunk: comparison between patients with motion-induced intermittent low back pain and healthy subjects.

STUDY DESIGN

Postural changes and trunk muscle activities were examined in patients with motion-induced intermittent low back pain (MILBP) and healthy controls.

OBJECTIVES

To assess the ability to maintain an upright standing position.

SUMMARY OF BACKGROUND DATA

Since MILBP is not observed at rest, its pathophysiology is complicated to investigate. METHODS.: Postural changes were measured with a 3-dimensional motion analyzer, and muscle activities with a surface electromyography while 10 female patients at an average age of 76 years (MILBP group) and 10 healthy controls at an average age of 74 years (Control Group) were standing upright and loaded with 10-kg weights.

RESULTS

In the Control Group, no significant forward bending motion occurred. In the MILBP group, there was a temporal increase in forward bending at various speeds and at various time phases. In the MILBP group but not in the Control Group, the rate of changes in median power frequency of erector spinae muscle declined significantly as compared with that in the Control Group (P < 0.05).

CONCLUSIONS

These results indicated that fatigue of the back muscles occurred in MILBP patients and could be a pain generator in low back pain.