The characteristics of preferred low-back motion.

The purposes of this study were to identify the loading effects on preferred low-back motion and to determine the consistency of preferred low-back motion. Fifteen male and female volunteers served as subjects. Each subject performed four trials of repeated flexion and extension until either the subject became exhausted or for 120s. Each trial corresponded to a relative load of 0, 25, 50, and 75% of the subject's prerecorded maximum torque in isometric flexion. The subjects were instructed to perform the movements at their own pace and through their preferred movement range. The results showed that above the 25% resistance level, the increased loads were accompanied by decreased velocities, with the changes due to the cycle temporal characteristics. The increased loads also resulted in decreased cycle excursions, with these changes due to reductions in the extension endpoints. With increased resistances the descriptive parameters became more variable, with a trend of increased variability toward the latter portion of a trial.