Hettinga Florentina J, De Koning Jos J, Broersen Frank T, Van Geffen Paul, Foster Carl
Institute for Fundamental and Clinical Human Movement Sciences Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands.
Med Sci Sports Exerc. 2006 Aug;38(8):1484-91. doi: 10.1249/01.mss.0000228956.75344.91.
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.
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.
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.
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.
本研究旨在通过比较不同节奏的最大努力中功率输出和积分肌电图（iEMG）的变化，探讨中枢和外周疲劳对4000米自行车计时赛成绩的作用。
八名训练有素的男性进行了三次随机排序的计时赛，采用不同的节奏策略，其中前2000米被操控以产生递增、均匀和递减的功率输出曲线（分别为SUB、EVEN和SUPRA）。受试者被要求在尽可能短的时间内完成所有试验的最后2000米。测量股直肌（RF）、股外侧肌（VL）和股二头肌（BF）的iEMG、机械功率输出和气体交换变量。根据气体交换数据计算无氧和有氧对机械功率输出的贡献。
在SUB计时赛中，机械功率输出的增加总是与所有肌肉的iEMG增加相关。计时赛接近尾声时机械功率输出的下降也表现为除RF外所有肌肉的iEMG增加。将最后2000米区间与第一个区间进行比较，所有策略的有氧功率输出均增加。SUB中的无氧功率输出增加，EVEN和SUPRA中的无氧功率输出减少。
iEMG与机械功率输出模式之间的关系与外周疲劳一致，而不是机械功率输出的中枢下调。具体而言，无氧能量资源似乎在调节节奏策略中很重要。
