Resistance exercise training is a cornerstone in preventing age-related declines in muscle mass and strength, and fatigability of limb muscle is important to this adaptive response. It is unknown, however, whether fatigability and the underlying mechanisms differ between different resistance exercise protocols in young and older adults. The purpose of this study was to quantify the fatigability of the knee extensors and identify the mechanisms in 20 young (22.2 ± 1.3 yr, 10 women) and 20 older adults (73.8 ± 5.4 yr, 10 women) elicited by a single session of high- and low-load resistance exercise. One leg completed a high-load protocol with contractions performed as fast as possible (HL-fast, ~80% 1 Repetition Max, 1RM), and the contralateral leg a low-load protocol performed with slow contractions (LL-slow, ~30% 1RM, 6 s concentric, 6 s eccentric). Each exercise involved four sets of eight repetitions. Before and immediately following each set, maximal voluntary isometric contractions (MVC) were performed, and voluntary activation and contractile properties quantified using electrical stimulation. The reduction in MVC was greater following the LL-slow (20%) than the HL-fast (12%, P = 0.004), with no age or sex differences. Similarly, the reduction in the amplitude of the involuntary electrically-evoked twitch was greater in the LL-slow (14%) than the HL-fast (7%, P = 0.014) and correlated with the reduction in MVC (r = 0.546, P < 0.001), whereas voluntary activation decreased only for the LL-slow protocol (5%, P < 0.001). Thus, low-load resistance exercise with slow contractions induced greater fatigability within the muscle than a more traditional high-load resistance protocol for both young and older men and women.

抗阻运动训练是预防与年龄相关的肌肉质量和力量下降的基石，而肢体肌肉的易疲劳性对于这种适应性反应很重要。然而，目前尚不清楚年轻人和老年人的不同抗阻运动方案之间的易疲劳性和潜在机制是否不同。本研究的目的是量化膝关节伸肌的疲劳性，并确定 20 名年轻人（22.2 ± 1.3 岁，10 名女性）和 20 名老年人（73.8 ± 5.4 岁，10 名女性）单次高- 和低负荷阻力运动。一条腿完成了高负荷方案，尽可能快地收缩（HL-fast，~80% 1 Repetition Max，1RM），对侧腿完成低负荷方案，缓慢收缩（LL-slow，~30 % 1RM，6 秒同心，6 秒偏心）。每个练习包括四组八次重复。在每组之前和之后立即进行最大自愿等长收缩 (MVC)，并使用电刺激量化自愿激活和收缩特性。LL-slow (20%) 后 MVC 的减少比 HL-fast (12%,P  = 0.004），没有年龄或性别差异。类似地，LL-slow (14%) 的非自愿电诱发抽搐幅度的降低大于 HL-fast (7%, P  = 0.014)，并且与 MVC 的降低相关 ( r  = 0.546, P  < 0.001），而自愿激活仅在 LL-slow 方案中降低（5%，P  < 0.001）。因此，对于年轻和年长的男性和女性来说，与更传统的高负荷抗阻训练相比，缓慢收缩的低负荷抗阻运动会导致肌肉更易疲劳。