Length-specific impairment of skeletal muscle contractile function after eccentric muscle actions in man

1. The effects of maximum voluntary eccentric muscle actions on forearm flexor strength were studied at three different elbow joint angles (0.87, 1.57 and 2.79 rad) to examine whether subsequent impairment of contractile function is muscle length-specific. 2. A bout of 70 maximum voluntary eccentric muscle actions performed with the forearm flexors elicited delayed muscle soreness, efflux of creatine kinase into the blood, loss of elbow joint range of motion and a prolonged decline in maximum voluntary isometric contraction torque at the three elbow angles monitored (P < 0.01) in 30 subjects. 3. The relative decline in maximum voluntary isometric contraction torque after eccentric exercise differed between elbow angles (P < 0.01). The greatest decline in strength relative to baseline was observed at the most acute elbow angle of 0.87 rad, followed by 1.57 and 2.79 rad respectively. Superimposed electrical stimulation in a subgroup of eight subjects did not increase the torque elicited by the forearm flexors during maximum voluntary contraction tests at the most acute elbow angle (0.87 rad) at any time-point after eccentric exercise, suggesting the disproportionate loss of strength at short muscle length was not due to the inhibitory effects of muscle soreness. 4. Measures of arm circumference and ability to fully flex the elbow (in the same subgroup of eight subjects) suggested the greater decline in strength at the acute elbow angle was not due to the possible confounding influences of muscle swelling and/or impaired muscle shortening ability on strength measurements at short muscle length. 5. These data suggest a shift in the forearm flexor length-tension relationship could account for the disparate decline in strength between elbow angles after eccentric exercise. The disproportionate loss of strength at short muscle length suggests that eccentric exercise evoked a subtle increase in muscle length, perhaps attributable to the cumulative effects of regions of lengthened sarcomeres and/or series elastic elements.