Abstract des Autors

There is considerable discrepancy in the literature as to the role that various mechanisms (e.g. neural, elastic, cross-bridge force potentiation, etc.) play to enhance muscle-tendon force output during a stretch shortening cycle (SSC). The purpose of this study was to determine if cross-bridge force potentiation contributes to the muscle-tendon force enhancement (MFE) that occurs during a SSC. Further, the relative contributions to MFE made by elastic and neural factors were evaluated. A Lido Active Multi-Joint II System was used to record and control knee joint torque and kinematics from 8 subjects performing knee extension movements. Subjects were required to extend their knee with a maximum effort both in a purely concentric mode of muscle action and in a mode involving a SSC. MFE was defined at specific joint angles as the joint torque determined from a SSC trial divided by the joint torque determined from a purely concentric trial. MFE values larger than 1.0 indicated a positive effect due to the SSC. It was found that: (1) under isokinetic conditions a SSC of the quadriceps muscles elicited MFE greater than 1.0 for the first 10-20ø of concentric motion, but this value dropped below 1.0 for greater motion, (2) neural factors were the primary contributors to MFE for the SSC conditions used in this study, and (3) there was no evidence that cross-bridge force potentiation occurred. Verf.-Referat