Effects of fatigue on the torque-velocity relation in muscle.

BACKGROUND The extent to which fatigue is related to the velocity of shortening is still not fully understood. OBJECTIVES To examine the effects of fatigue induced by maximal intensity exercise at different velocities on subsequent torque-velocity relations in muscle. METHODS Ten men (mean (SD) age 25 (3) years; stature 1.78 (0.34) m; body mass 80.6 (14.5) kg) provided written informed consent and, over a five day period in a randomised manner, performed 16 fatiguing bouts of maximal intensity exercise on an isokinetic dynamometer each followed by one repetition maximum action. Concentric peak torque of the preferred leg was assessed at angular velocities of 0.52, 1.05, 2.09, and 3.14 rad/s. Mechanical work performed for all fatiguing bouts was held at 3050-3150 J. After a 45 second rest, a maximum effort was performed at one of the preset velocities. As a baseline, dependent variables of peak torque (N.m), angle of peak torque (rad), and mean torque (N.m) were measured at each velocity. An analysis of covariance was used to compare torque-velocity relations, and one factor, within subject analyses of variance with repeated measures investigated differences from baseline. RESULTS Torque-velocity relations for all dependent variables did not differ (p>0.05). Similarly, angles at which peak torque occurred were not velocity dependent and did not differ from baseline and subsequent exercise measures (p>0.05). Generally, fatiguing exercise at low velocities led to reductions in peak and mean torque in subsequent exercise at higher velocities (p<0.05). CONCLUSIONS Torque-velocity relations fundamentally remain intact after fatigue induced at any velocity, although the magnitude changes. The results suggest that the greater decline in torque during subsequent exercise at high velocities could be due to greater exhaustion of fatigue sensitive type II fibres, whereas low velocity subsequent exercise is less affected because of the greater use of type I fibres.