Motor impairment in the human hand following eccentric exercise

Motor impairment was induced by having subjects perform two sets of 50 maxi mal contractions, using the first dorsal interosseus (FDI) muscle to abduct the index finger, while the muscle was being stretched. Tests were conduct ed prior to the exercise (pre-exercise) and 24 h following the exercise (po st-exercise). There were declines of 19% in maximal abduction torque and 15 % in maximal flexion torque at the metacarpapha-langeal joint, during isome tric contraction post-exercise compared to pre-exercise. The ability to sta bilize the metacarpophalangeal joint about the abduction/adduction axis was reduced by 14% post-exercise? and the variability in tracking an isometric torque target increased by 30%. There was a decrement of 7%-10% in the med ian frequency of the power density spectrum of FDI electromyogram (EMG) thr oughout a 60 s maintained abduction at 50% maximal voluntary contraction. T he mean rectified EMG, on the other hand, increased by 100%-175% for torque levels below 40% of maximal voluntary contraction? post-exercise. The resu lts were consistent with preferential injury of type II muscle fibres in FD I. Although non-exercised synergist muscles appeared to be inhibited during maximal voluntary flexion, there was evidence that they compensated for in jured FDI muscle fibres during maintained contraction at sub-maximal flexio n torque.