The aim of the present study was to determine the magnitude of the maximal level of peripheral fatigue attainable (fatigue threshold) during all-out intermittent isometric knee-extensor protocol in both young (24±1years, N=12) and older participants (60±2years, N=12) to provide new insights on the effects of aging on neuromuscular function. Participants performed two experimental sessions, in which they performed 60 maximal voluntary contractions (MVC; 3s-contraction, 2s-relaxation). One trial was performed in the unfatigued state (CTRL) and one other following fatiguing neuromuscular electrical stimulation of the quadriceps (F_NMES). Peripheral fatigue was quantified via pre/post-exercise decrease in quadriceps twitch-force (∆P_tw). Critical force (CF) was determined as the mean force output of the last 12 contractions while W′ was calculated as the area above CT. While F_NMES led to significant decrease in P_tw prior to performing the 60 MVCs protocol (P<0.05), ∆P_tw was not different between CTRL and F_NMES for both the young (P=0.49) and the old (P=0.52) group. However, this peripheral fatigue threshold was significantly greater in young vs old participants (∆P_tw = -48±10 vs -29±13%, respectively, P<0.05). In CTRL, W' was 55 ± 13 % lower in the old compared to the young group (P<0.01), but CT was similar (326±10 vs 322±12N, respectively, P=0.94). ∆P_tw was correlated with W', independently of age (r²=0.84, P<0.001). Exercise performance decreases with aging consequent to a lower tolerance to peripheral fatigue. However, the peripheral fatigue threshold mechanism persists with healthy aging and continues to play its protective role to preserve locomotor muscle function during exercise

中文翻译：

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衰老降低了可忍受的周围疲劳的最大程度，并削弱了运动能力。

本研究的目的是确定年轻（24±1岁，N = 12）和年长参与者（60岁）在全部间歇性等距伸膝方案中可达到的最大周围疲劳程度（疲劳阈值）的大小。 ±2年，N = 12），以提供有关衰老对神经肌肉功能影响的新见解。参与者进行了两次实验，其中他们进行了60次最大的自愿收缩（MVC； 3s收缩，2s放松）。在对四头肌进行神经肌肉电刺激（F _NMES）疲劳后，进行了一项以疲劳状态（CTRL）进行的试验，另一项试验。通过运动前后股四头肌抽搐力的降低（_ΔPtw）。临界力（CF）被确定为最后12次收缩的平均力输出，而W'被计算为CT上方的面积。尽管F _NMES在执行60 MVC协议之前导致P _tw显着降低（P <0.05），但对于年轻（P = 0.49）和老（P = 0.52）而言，CTRL和F _NMES之间的∆P _tw并无差异。）组。但是，该年龄疲劳阈值在年轻参与者和老年参与者中明显更高（分别为∆P _tw = -48±10 vs -29±13％，P <0.05）。在CTRL中，老年组的W'比年轻组降低了55±13％（P <0.01），但CT值相似（分别为326±10 vs 322±12N，P = 0.94）。∆P _tw与W'相关，与年龄无关（r² = 0.84，P <0.001）。运动能力随着年龄的增长而降低，从而降低了对周围疲劳的承受能力。然而，外周疲劳阈值机制随着健康的衰老而持续存在，并在运动过程中继续发挥其保护运动肌功能的保护作用