School of Kinesiology, The University of Western Ontario, London, ON, Canada.
Appl Physiol Nutr Metab. 2009 Oct;34(5):866-74. doi: 10.1139/H09-085.
The present study was designed to compare the relative influence of various fatigue-related factors involved in isometric and dynamic task failure following an equivalent decrease in isometric maximum voluntary contraction (MVC) torque. Using a similar duty cycle (~1-s contraction per 2 s) and contraction load (50% of MVC), 9 young males performed in the dorsiflexors a dynamic task, and on a separate occasion an intermittent isometric task, to an equal decrease in isometric MVC torque. Dynamic contractions had greater motor unit activation and maximum rate of torque development, and required fewer contractions to task failure than the isometric task, indicating a faster development of fatigue during the velocity-dependent dynamic contractions. Peripheral factors, rather than impairments in voluntary drive, were responsible for the equivalent decrease in MVC torque at task failure and its subsequent incomplete recovery. These included, for both tasks, similar changes during fatigue and recovery in voluntary isometric MVC torque, shortening velocity, stimulated twitch and 50 Hz torque, and 50 Hz maximum rate of relaxation. Irrespective of the task, however, the greater reduction in shortening velocity at task failure and its subsequent faster recovery than MVC torque suggest that changes in metabolites affect velocity to a greater extent than isometric torque.
本研究旨在比较等长最大自主收缩（MVC）力矩下降后，参与等长和动态任务失败的各种与疲劳相关因素的相对影响。使用类似的工作周期（每 2 秒收缩 1 秒）和收缩负荷（MVC 的 50%），9 名年轻男性在背屈肌中进行动态任务，并且在另一个时间进行间歇性等长任务，直到等长 MVC 力矩相等下降。与等长任务相比，动态收缩具有更大的运动单位激活和最大扭矩发展率，并且需要更少的收缩才能达到任务失败，这表明在依赖速度的动态收缩过程中更快地产生疲劳。在任务失败及其随后的不完全恢复时，是外周因素而不是自愿驱动的损伤导致 MVC 扭矩的等效下降。这包括在疲劳和恢复期间，两种任务的自愿等长 MVC 扭矩、缩短速度、刺激抽搐和 50Hz 扭矩以及 50Hz 最大松弛率都相似。然而，无论任务如何，在任务失败时缩短速度的较大减少及其随后比 MVC 扭矩更快的恢复表明代谢物的变化对速度的影响大于等长扭矩。
