Purpose Although high-velocity contractions elicit greater muscle fatigue in older than young adults, the cause of this difference is unclear. We examined the potential roles of resting muscle architecture and baseline contractile properties, as well as changes in voluntary activation and low-frequency fatigue in response to high-velocity knee extensor work. Methods Vastus lateralis muscle architecture was determined in quiescent muscle by ultrasonography in 8 young (23.4±1.8 yrs) and 8 older women (69.6±1.1 yrs). Maximal voluntary dynamic (MVDC) and isometric (MVIC), and stimulated (80 Hz and 10 Hz, 500 ms) isometric contractions were performed before and immediately after 120 MVDCs (240° . s -1 , one every 2 s). Results Architecture variables did not differ between groups (p≥0.209), but the half-time of torque relaxation (T 1/2 ) was longer in older than young women at baseline (151.9±6.0 vs. 118.8±4.4 ms, respectively, p=0.001). Older women fatigued more than young (to 33.6±4.7 % vs. 55.2±4.2 % initial torque, respectively; p=0.004), with no evidence of voluntary activation failure (?MVIC:80Hz torque) in either group (p≥0.317). Low-frequency fatigue (?10:80Hz torque) occurred in both groups (p<0.001), as did slowing of T 1/2 (p=0.001), with no differences between groups. Baseline T 1/2 was inversely associated with fatigue in older (r 2 =0.584, p=0.045), but not young women (r 2 =0.147, p=0.348). Conclusions These results indicate that differences in muscle architecture, voluntary activation, and low-frequency fatigue do not explain the greater fatigue of older compared with young women during high-velocity contractions. The inverse association between baseline T 1/2 and fatigue in older women suggests that factors related to slower muscle contractile properties may be protective against fatigue during fast, repetitive contractions in aging.

中文翻译：

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老年对膝盖伸肌疲劳和高速肌肉收缩恢复的影响

目的尽管与老年人相比，高速收缩引起的肌肉疲劳更大，但这种差异的原因尚不清楚。我们研究了静息肌肉结构和基线收缩特性的潜在作用，以及响应于高速膝盖伸肌工作的自愿性激活和低频疲劳的变化。方法对8例年轻（23.4±1.8岁）和8例老年妇女（69.6±1.1岁）进行超声检查，以静息肌的方式测定外侧阔肌的结构。在120个MVDCs（240°.s -1，每2s一次）之前和之后立即进行最大自愿动态（MVDC）和等距（MVIC），以及受激（80 Hz和10 Hz，500 ms）等距收缩。结果架构变量在各组之间没有差异（p≥0.209），但在基线时，老年女性的扭矩松弛半衰期（T 1/2）长于年轻女性（分别为151.9±6.0 vs. 118.8±4.4 ms，p = 0.001）。老年女性比年轻女性疲劳程度更高（分别为33.6±4.7％和55.2±4.2％初始扭矩； p = 0.004），两组均无自发性激活失败的证据（？MVIC：80Hz扭矩）（p≥0.317）。 。两组均出现低频疲劳（？10：80Hz扭矩）（p <0.001），T 1/2的减速也是如此（p = 0.001），两组之间无差异。基线T 1/2与老年人的疲劳成反比（r 2 = 0.584，p = 0.045），而与年轻女性无关（r 2 = 0.147，p = 0.348）。结论这些结果表明，在高速收缩过程中，与年轻女性相比，肌肉结构，自发性激活和低频疲劳的差异不能解释老年人的疲劳程度。