School of Kinesiology, The University of Western Ontario, London, Ontario, Canada.
J Appl Physiol (1985). 2012 Dec 15;113(12):1821-30. doi: 10.1152/japplphysiol.00879.2012. Epub 2012 Oct 18.
Fatigability is highly task dependent wherein motor unit (MU) discharge rates and recruitment thresholds are affected differently depending on whether contractions are performed at maximal or submaximal intensities. Although much is described for isometric tasks, the behavior of MU properties during the production of maximal velocity dynamic contractions following submaximal fatiguing contractions is unknown. In seven young men, we evaluated changes in MU recruitment thresholds and MU discharge rates of the anconeus muscle during both submaximal and maximal dynamic elbow extensions following a submaximal dynamic fatiguing protocol of moderate intensity to velocity task failure. Velocity and power of the maximal dynamic contractions declined ∼45 and ∼55%, respectively, but these variables were unchanged for the submaximal target velocity contractions. Discharge rates of the 12 MUs at task failure were unchanged for submaximal dynamic contractions, but were decreased ∼20% for maximal dynamic and ballistic isometric contractions at task failure. MU recruitment thresholds of submaximal dynamic contractions decreased 52% at task failure, but were similar throughout the fatiguing protocol for maximal contractions. These findings support the concept of a common neural mechanism responsible for the relative declines in MU discharge rate associated with submaximal fatigability in both isometric and dynamic contractions.
疲劳性高度依赖于任务，其中运动单位（MU）的放电率和募集阈值会根据收缩是在最大还是次最大强度下进行而受到不同的影响。尽管已经对等长任务进行了大量描述，但在次最大疲劳收缩后进行最大速度动力收缩时 MU 特性的行为尚不清楚。在七名年轻男性中，我们评估了在次最大动态疲劳方案后，进行最大动态肘部伸展时，肱三头肌 MU 募集阈值和 MU 放电率的变化。最大动态收缩的速度和功率分别下降了约 45%和 55%，但这些变量对于次最大目标速度收缩保持不变。在任务失败时，12 个 MU 的放电率对于次最大动态收缩保持不变，但对于最大动态和弹道等长收缩在任务失败时下降了约 20%。在任务失败时，次最大动态收缩的 MU 募集阈值下降了 52%，但在最大收缩的疲劳方案中保持相似。这些发现支持了一个共同的神经机制的概念，该机制负责与等长和动力收缩中的次最大疲劳性相关的 MU 放电率的相对下降。
