Pacing strategy and the occurrence of fatigue in 4000-m cycling time trials.

PURPOSE The present study was designed to examine the role of central and peripheral fatigue on 4000-m cycling time trial performance by comparing changes in power output and integrated electromyography (iEMG) in differently paced maximal efforts. METHODS Eight well-trained men performed three randomly ordered time trials with different pacing strategies, in which the first 2000 m were manipulated to evoke an increasing, even, and decreasing power output profile (SUB, EVEN, and SUPRA, respectively). Subjects were instructed to finish the last 2000 m of all trials in the shortest time possible. iEMG of the rectus femoris (RF), vastus lateralis (VL), and biceps femoris (BF) muscle, mechanical power output, and gas exchange variables were measured. Anaerobic and aerobic contributions to mechanical power output were calculated from gas exchange data. RESULTS The increase in mechanical power output during the SUB time trials was always associated with an increase in iEMG in all muscles. A decrease in mechanical power output near the end of the time trials was also marked by an increase in iEMG for all muscles, except for the RF. Comparing the last 2000-m interval with the first, aerobic power output increased for all strategies. Anaerobic power output increased in SUB and decreased in EVEN and SUPRA. CONCLUSION The relationship between iEMG and mechanical power output pattern was consistent with peripheral fatigue rather than central downregulation of mechanical power output. Specifically, anaerobic energy resources seem to be important in regulating pacing strategy.