Changes in Passive Muscle Stiffness Following Eccentric Exercise

Abstract

0138 PURPOSE: Limited published data exist quantifying the changes in passive muscle stiffness following damaging eccentric exercise. The purpose of this study was to quantify the changes in passive stiffness of the knee extensors following a bout of eccentric exercise. METHODS: Nine subjects (4 women, 5 men; age 35±5 yr) performed 120 isokinetic eccentric knee extension contractions (60°/s) at 90% of maximum isometric strength. Isometric strength, passive stiffness and quadriceps pain were recorded prior to eccentric exercise, immediately post-exercise, and on the three subsequent days. Isometric strength was measured at 70° knee flexion. Passive stiffness was defined as the increase in torque during passive knee flexion from 70° to 110° at 5°/s. Surface EMG recordings were used to verify muscle relaxation during stretch. Quadriceps pain was measured on a scale of 0–10 (0 = no discomfort, 10 = walking with a limp). Data were analyzed using repeated measures analysis of variance. RESULTS: There was significant strength loss (P<0.05) and pain (P<0.01) following the eccentric exercise, peaking two days post-exercise (strength loss 25%, pain 4.1/10). There was no significant change in passive stiffness (P = 0.25): stiffness was 110% of baseline immediately post-exercise and 97%, 103% and 99% of baseline on the subsequent three days. CONCLUSION: Previous studies (Whitehead et al 2001; Howell et al 1993) have demonstrated dramatic increases in passive muscle stiffness in the plantarflexors (140% of baseline) and elbow flexors (200% of baseline) following damaging bouts of eccentric exercise. By contrast, in the present study, stiffness in the knee extensors was not increased, despite marked strength loss and pain. Stiffness changes following eccentric exercise appear to be independent of other symptoms of damage and may be more dependent on the size of the exercising muscle group.