Trunk muscle strength in eccentric and concentric lateral flexion

The aim of this study was to investigate the position and velocity dependen cy of the strength (torque) output of lateral flexor muscles of the trunk. Twelve male volunteers with no history of back pain participated. Movement was constrained to the frontal plane and the velocity was controlled by an isokinetic dynamometer. The eccentric and concentric strength of lateral fl exor muscles on the left side was measured in a supine position at velociti es of 15, 30, 45 and 60 degrees .s(-1) and static strength at 20, 10, 0, -1 0 and -20 degrees of lateral trunk flexion. Average peak torque values rang ed between 211 and 218 Nm (eccentric) and between 66 and 140 Nm (concentric ) over all tested velocities, and the average static torque ranged between 80 and 172 Nm over all tested positions. The shape of the torque-position c urves was unaffected by speed and peak torque occurred at an average positi on of 11-15 degrees to the contralateral (right) side in both eccentric and concentric actions. In eccentric actions, torque output was significantly higher than that during concentric and static actions. Increasing the speed of contraction did not affect eccentric torque values, whereas both peak a nd angle-specific concentric torque decreased with increasing speed. These results are in general accordance with earlier findings from other muscle g roups, such as the knee extensors. However, they are partially at variance with results obtained in studies of lateral lifting and lowering, indicatin g that there are other limiting factors in complex tasks that do not just i nvolve the trunk muscles.