Hunter Sandra K, Butler Jane E, Todd Gabrielle, Gandevia Simon C, Taylor Janet L
Exercise Science Program, Department of Physical Therapy, PO Box 1881, Marquette University, Milwaukee, WI 53201, USA.
J Appl Physiol (1985). 2006 Oct;101(4):1036-44. doi: 10.1152/japplphysiol.00103.2006. Epub 2006 May 25.
Young women are less fatigable than young men for maximal and submaximal contractions, but the contribution of supraspinal fatigue to the sex difference is not known. This study used cortical stimulation to compare the magnitude of supraspinal fatigue during sustained isometric maximal voluntary contractions (MVCs) performed with the elbow flexor muscles of young men and women. Eight women (25.6 +/- 3.6 yr, mean +/- SD) and 9 men (25.4 +/- 3.8 yr) performed six sustained MVCs (22-s duration each, separated by 10 s). Before the fatiguing contractions, the men were stronger than the women (75.9 +/- 9.2 vs. 42.7 +/- 8.0 N.m; P < 0.05) in control MVCs. Voluntary activation measured with cortical stimulation before fatigue was similar for the men and women during the final control MVC (95.7 +/- 3.0 vs. 93.3 +/- 3.6%; P > 0.05) and at the start of the fatiguing task (P > 0.05). By the end of the six sustained fatiguing MVCs, the men exhibited greater absolute and relative reductions in torque (65 +/- 3% of initial MVC) than the women (52 +/- 9%; P < 0.05). The increments in torque (superimposed twitch) generated by motor cortex stimulation during each 22-s maximal effort increased with fatigue (P < 0.05). Superimposed twitches were similar for men and women throughout the fatiguing task (5.5 +/- 4.1 vs. 7.3 +/- 4.7%; P > 0.05), as well as in the last sustained contraction (7.8 +/- 5.9 vs. 10.5 +/- 5.5%) and in brief recovery MVCs. Voluntary activation determined using an estimated control twitch was similar for the men and women at the start of the sustained maximal contractions (91.4 +/- 7.4 vs. 90.4 +/- 6.8%, n = 13) and end of the sixth contraction (77.2 +/- 13.3% vs. 73.1 +/- 19.6%, n = 10). The increase in the area of the motor-evoked potential and duration of the silent period did not differ for men and women during the fatiguing task. However, estimated resting twitch amplitude and the peak rates of muscle relaxation showed greater relative reductions at the end of the fatiguing task for the men than the women. These results indicate that the sex difference in fatigue of the elbow flexor muscles is not explained by a difference in supraspinal fatigue in men and women but is largely due to a sex difference of mechanisms located within the elbow flexor muscles.
在进行最大收缩和次最大收缩时，年轻女性比年轻男性更不易疲劳，但脊髓上疲劳对这种性别差异的影响尚不清楚。本研究采用皮层刺激来比较年轻男性和女性在用肘屈肌进行持续等长最大自主收缩（MVC）期间脊髓上疲劳的程度。八名女性（25.6±3.6岁，平均值±标准差）和九名男性（25.4±3.8岁）进行了六次持续的MVC（每次持续22秒，间隔10秒）。在疲劳性收缩之前，在对照MVC中男性比女性更强（75.9±9.2对42.7±8.0牛·米；P<0.05）。在最后一次对照MVC期间以及疲劳任务开始时，通过皮层刺激测量的男性和女性的自主激活相似（95.7±3.0对93.3±3.6%；P>0.05）。到六次持续的疲劳性MVC结束时，男性的扭矩绝对和相对降低幅度（初始MVC的65±3%）大于女性（52±9%；P<0.05）。在每次22秒的最大努力期间，运动皮层刺激产生的扭矩增加（叠加抽搐）随疲劳而增加（P<0.05）。在整个疲劳任务中，男性和女性的叠加抽搐相似（5.5±4.1对7.3±4.7%；P>0.05），在最后一次持续收缩中（7.8±5.9对10.5±5.5%）以及短暂恢复MVC中也是如此。在持续最大收缩开始时（91.4±7.4对90.4±6.8%，n = 13）和第六次收缩结束时（77.2±13.3%对73.1±19.6%，n = 10），使用估计的对照抽搐确定的男性和女性的自主激活相似。在疲劳任务期间，男性和女性的运动诱发电位面积增加和静息期持续时间没有差异。然而，在疲劳任务结束时，男性的估计静息抽搐幅度和肌肉松弛峰值率的相对降低幅度大于女性。这些结果表明，肘屈肌疲劳的性别差异不能用男性和女性脊髓上疲劳的差异来解释，而很大程度上是由于肘屈肌内机制的性别差异。
