Hikosaka Mikito, Aramaki Yu
Graduate School of Health and Sport Sciences, Chukyo University, Aichi, Japan.
School of Health and Sport Sciences, Chukyo University, Aichi, Japan.
Front Hum Neurosci. 2021 Nov 2;15:763580. doi: 10.3389/fnhum.2021.763580. eCollection 2021.
Simultaneous bimanual movements are not merely the sum of two unimanual movements. Here, we considered the unimanual/bimanual motor system as comprising three components: unimanual-specific, bimanual-specific, and overlapping (mobilized during both unimanual and bimanual movements). If the force-generating system controlling the same limb differs between unimanual and bimanual movements, unimanual exercise would be expected to fatigue the unimanual-specific and overlapping parts in the force-generating system but not the bimanual-specific part. Therefore, we predicted that the decrease in bimanual force generation induced by unimanual neuromuscular fatigue would be smaller than the decrease in unimanual force generation. Sixteen healthy right-handed adults performed unimanual and bimanual maximal handgrip measurements before and after a submaximal fatiguing handgrip task. In the fatigue task, participants were instructed to maintain unimanual handgrip force at 50% of their maximal handgrip force until the time to task failure. Each participant performed this task in a left-hand fatigue (LF) condition and a right-hand fatigue (RF) condition, in a random order. Although the degree of neuromuscular fatigue was comparable in both conditions, as expected, the decrease in bimanual right handgrip force was significantly smaller than those during unimanual right performance in the RF condition, but not in the LF condition. These results indicate that for the right-hand, neuromuscular fatigue in unimanual handgrip does not completely affect simultaneous bimanual handgrip. Regarding the underlying mechanisms, we propose that although neuromuscular fatigue caused by unimanual handgrip reduces the motor output of unimanual-specific and overlapping parts in the force-generating system, when simultaneous bimanual handgrip is performed, the overlapping part (which is partially fatigued) and the bimanual-specific part (which is not yet fatigued) generate motor output, thus decreasing the force reduction.
同时进行的双手运动并非仅仅是两个单手运动的总和。在此，我们认为单手/双手运动系统由三个部分组成：单手特异性部分、双手特异性部分以及重叠部分（在单手和双手运动中均被调动）。如果控制同一肢体的力产生系统在单手和双手运动之间存在差异，那么单手运动预计会使力产生系统中的单手特异性部分和重叠部分疲劳，但不会使双手特异性部分疲劳。因此，我们预测单手神经肌肉疲劳引起的双手力产生下降将小于单手力产生的下降。16名健康的右利手成年人在进行次最大疲劳握力任务前后，分别进行了单手和双手最大握力测量。在疲劳任务中，参与者被要求将单手握力维持在其最大握力的50%，直到任务失败。每位参与者以随机顺序在左手疲劳（LF）条件和右手疲劳（RF）条件下执行此任务。尽管在两种条件下神经肌肉疲劳程度相当，但正如预期的那样，在RF条件下，双手右手握力的下降明显小于单手右手执行时的下降，但在LF条件下并非如此。这些结果表明，对于右手而言，单手握力的神经肌肉疲劳并不会完全影响同时进行的双手握力。关于潜在机制，我们提出，尽管单手握力引起的神经肌肉疲劳会降低力产生系统中单手特异性部分和重叠部分的运动输出，但当进行同时的双手握力时，重叠部分（部分疲劳）和双手特异性部分（尚未疲劳）会产生运动输出，从而减少了力的下降。
