Superficial lumbopelvic muscle overactivity and decreased cocontraction after 8 weeks of bed rest.

Study Design: Longitudinal study.

Objective: To gain insight into the effects of inactivity on lumbopelvic stabilization.

Summary Of Background Data: Some authors have suggested a link between inactivity and lumbopelvic (LP) pain. Studies examining the superficial musculature in LP pain have shown overactivity and increased cocontraction. Studies in inactivity (bed rest, microgravity) have shown similar effects on the musculature of the legs. Here we examine the effect of bed rest on superficial LP activity and cocontraction.

Methods: Ten male subjects participated in the "Berlin Bed Rest Study" and underwent 8 weeks of bed rest with a 1-year follow-up. A repetitive knee movement model at four movement speeds in non-weightbearing was used to assess, via electromyography, activity (amplitude-ratios) in five superficial LP muscles and abdominal flexor-lumbar extensor cocontraction for LP stabilization. Testing was conducted at regular intervals during and after bed rest.

Results: Analysis of the amplitude-ratio data showed a significant effect of testing date (F = 2.38, P = 0.005). This effect was generalized across all muscles, however (F = 0.59, P = 0.989). During bed rest, subjects exhibited higher levels of activity but lower levels of cocontraction (F = 8.84, P < 0.001), and the changes were still present up to 1 year after bed rest.

Conclusions: The bed rest protocol resulted in the development of superficial muscle overactivity but decreased cocontraction. These changes could reflect dysfunction of central nervous system control of LP stabilization. These changes were still apparent 1 year after bed rest, suggesting a stable change in motor control.