Activation among the elbow flexor muscles differs when maintaining arm position during a fatiguing contraction
Activation among the elbow flexor muscles differs when maintaining arm position during a fatiguing contraction
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DOI：
10.1152/japplphysiol.01038.2002
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发表时间：
2003-06-01
影响因子：
3.3
通讯作者：
Enoka, RM
中科院分区：
文献类型：
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作者：
Hunter, SK;Lepers, R;Enoka, RM
24 名男性 (n = 11) 和女性 (n = 13) 尽可能长时间地用肘部屈肌支撑相当于最大自主收缩力 20% 的惯性负载，同时保持肘部角度恒定在 90 度。执行任务的 3 次耐力时间没有差异（320 +/- 149 秒；P > 0.05），女性（360 +/- 168 秒）和男性（273 +/- 108 秒；P = 0.11）之间没有差异。各疗程中肘屈肌平均肌电图 (EMG) 的增加率相似 ( P > 0.05)。然而，在疲劳任务期间，肱二头肌长头、肱桡肌和肱肌的平均肌电图有所增加（P<0.05），但肱二头肌短头则没有增加。此外，与其他肘屈肌相比，肱肌在收缩开始和结束时的平均肌电图更大。肌电图活动的爆发率在疲劳收缩期间增加，并且与其他肘屈肌（0.5 +/- 0.1 爆发/分钟）相比，肱肌（1.0 +/- 0.2 爆发/分钟）更高。疲劳收缩过程中加速度、平均动脉压和心率的标准差的变化在各个疗程中是相似的。这些发现表明，肌电图活动反映了脊髓中运动神经元接收到的净兴奋性和抑制性输入，在维持位置任务的重复过程中不具有适应性。此外，这些结果与之前的研究（Hunter SK 和 Enoka RM. J Appl Physiol 94：108 - 118，2003）形成对比，当时等长收缩的目标是保持恒定的力。这些来自对肘屈肌的一系列研究的结果表明，疲劳收缩期间支撑的负载类型会影响耐力时间随着任务重复执行而变化的程度。
Twenty-four men (n = 11) and women ( n = 13) supported an inertial load equivalent to 20% of the maximum voluntary contraction force with the elbow flexor muscles for as long as possible while maintaining a constant elbow angle at 90degrees. Endurance time did not differ on the three occasions that the task was performed ( 320 +/- 149 s; P > 0.05), and there was no difference between women ( 360 +/- 168 s) and men ( 273 +/- 108 s; P = 0.11). The rate of increase in average electromyogram (EMG) for the elbow flexor muscles was similar across sessions ( P > 0.05). However, average EMG during the fatiguing task increased for the long head of biceps brachii, brachioradialis, and brachialis ( P < 0.05) but not for the short head of biceps brachii. Furthermore, the average EMG for the brachialis was greater at the start and end of the contraction compared with the other elbow flexor muscles. The rate of bursts in EMG activity increased during the fatiguing contraction and was greater in brachialis (1.0 +/- 0.2 bursts/min) compared with the other elbow flexor muscles (0.5 +/- 0.1 bursts/min). The changes in the standard deviation of acceleration, mean arterial pressure, and heart rate during the fatiguing contractions were similar across sessions. These findings indicate that the EMG activity, which reflects the net excitatory and inhibitory input received by the motoneurons in the spinal cord, was not adaptable over repeat sessions for the maintain-position task. Furthermore, these results contrast those from a previous study ( Hunter SK and Enoka RM. J Appl Physiol 94: 108 - 118, 2003) when the goal of the isometric contraction was to maintain a constant force. These results, from a series of studies on the elbow flexor muscles, indicate that the type of load supported during the fatiguing contraction influences the extent to which endurance time can change with repeat performances of the task.