Passive and active wrist joint stiffness following eccentric exercise

The purpose of this study was to investigate the effects of exercise-induce d muscle injury on passive and active wrist joint stiffness. Ten male subje cts were repeatedly tested over a period of 11 days, once prior to, and fou r times following a bout of eccentric exercise with the wrist extensor musc les. Static wrist stiffness was measured by applying a 3 degrees ramp and h old displacement of the manipulandum, which stretched the wrist extensor mu scles. Wrist extension maximum voluntary contraction (MVC) declined by 24.5 % from pre-exercise to 24 h after the exercise bout (P < 0.001). There was a reduced passive range of motion (ROM) from 82.8 degrees pre-exercise to 7 0.2 degrees on day 1 (P < 0.01), but no change in the passive joint stiffne ss at the neutral joint position, suggesting mechanical changes in the non- contractile tissues, or swelling that only resisted movement at the extreme s of the ROM. Active joint stiffness at 50% preexercise MVC declined from 0 .299 Nm deg(-1) pre-exercise to 0.254 Nm deg(-1) on day 1 (P < 0.025). Acti ve joint stiffness at 10% pre-exercise MVC did not change on any of the day s of testing compared to pre-exercise. These findings may indicate that lar ge muscle fibers were more affected by the injury than small muscle fibers.