Task failure during fatiguing contractions performed by humans.
Task failure during fatiguing contractions performed by humans.
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DOI：
10.1152/japplphysiol.00207.2005
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发表时间：
2005-08
影响因子：
3.3
通讯作者：
K. Maluf;R. Enoka
中科院分区：
文献类型：
--
作者：
K. Maluf;R. Enoka
通过比较两次类似的疲劳收缩失败时发生的生理调整，可以确定限制更困难任务持续时间的机制。这种方法已被用来研究两个疲劳收缩，称为力和位置的任务，不同的反馈类型的主题和周围环境提供的支持量。即使这两个任务需要一个类似的净肌肉扭矩在次最大等长收缩，持续时间的位置任务可以持续的是一贯的更短的时间比力的任务。与力任务相比，位置任务的EMG活动增加率更高，运动单位招募和速率编码的变化更显著。这些观察结果是一致的假设，即运动单位池更迅速地招募位置任务。运动单位行为的差异似乎是由突触输入的变化引起的，可能涉及位置任务期间牵张反射的敏感性提高。在重复执行两个疲劳收缩，一些科目能够增加失败的时间为力的任务，但不是位置的任务。此外，失败的位置任务的时间可能会受到与保持肢体的位置相关的姿势要求的影响，并且当姿势活动引起升压反应时，两个持续时间的差异增强。这些观察结果表明，两种疲劳收缩持续时间的差异可归因于用于维持任务的控制策略和相关姿势活动的大小的差异。
By comparing the physiological adjustments that occur when two similar fatiguing contractions are performed to failure, it is possible to identify mechanisms that limit the duration of the more difficult task. This approach has been used to study two fatiguing contractions, referred to as the force and position tasks, which differed in the type of feedback given to the subject and the amount of support provided by the surroundings. Even though the two tasks required a similar net muscle torque during submaximal isometric contractions, the duration that the position task could be sustained was consistently much briefer than that for the force task. The position task involved a greater rate of increase in EMG activity and more marked changes in motor unit recruitment and rate coding compared with the force task. These observations are consistent with the hypothesis that the motor unit pool was recruited more rapidly during the position task. The difference in motor unit behavior appeared to be caused by variation in synaptic input, likely involving heightened sensitivity of the stretch reflex during the position task. Upon repeat performances of the two fatiguing contractions, some subjects were able to increase the time to failure for the force task but not the position task. Furthermore, the time to failure for the position task could be influenced by the postural demands associated with maintaining the position of the limb, and the difference in the two durations was enhanced when the postural activity evoked a pressor response. These observations indicate that the difference in the duration of the two fatiguing contractions was attributable to differences in the control strategy used to sustain the tasks and the magnitude of the associated postural activity.