背景:在积极延长或缩短收缩后,等距稳态扭矩增加(残余力增强;rFE)或减少(残余力降低;rFD),分别,与相同肌肉长度和激活水平下的固定端等距收缩相比。尽管这种历史依赖力的机制已经得到了广泛的研究,关于运动引起的肌无力对rFE和rFD的影响知之甚少。
目标:评估背屈的rFE和rFD为20%,60%,和100%最大自愿性扭矩(MVC)和激活匹配,并在20%MVC下进行电刺激,之前,1小时后,150次最大偏心背屈收缩后24小时。
方法:26名参与者(13名男性,24.7±2.0y;13名女性,22.5±3.6y)坐在测力计中,其右臀部和膝盖角度设置为110°和140°,分别,踝关节偏移设置在0°和40°之间的足底屈曲(PF)。MVC扭矩,峰值抽搐扭矩,和长时间的低频压力抑制被用来评估偏心运动引起的神经肌肉损伤。历史相关的收缩由1s等距(40°PF或0°PF)相位组成,1s的缩短或延长阶段(40°/s),和8s等距(0°PF或40°PF)相位。
结果:偏心运动后;MVC扭矩降低,长时间的低频压力存在,在所有最大和次最大条件下,rFE和rFD均增加。
结论:自愿性扭矩和激活匹配过程中力的历史依赖性,电刺激的收缩在偏心运动后被放大。看来,弱化的神经肌肉系统会放大力的历史依赖性的大小。
BACKGROUND: Following active lengthening or shortening contractions, isometric steady-state torque is increased (residual force enhancement; rFE) or decreased (residual force depression; rFD), respectively, compared to fixed-end isometric contractions at the same muscle length and level of activation. Though the mechanisms underlying this history dependence of force have been investigated extensively, little is known about the influence of exercise-induced muscle weakness on rFE and rFD.
OBJECTIVE: Assess rFE and rFD in the dorsiflexors at 20%, 60%, and 100% maximal voluntary torque (MVC) and activation matching, and electrically stimulated at 20% MVC, prior to, 1 h following, and 24 h following 150 maximal eccentric dorsiflexion contractions.
METHODS: Twenty-six participants (13 male, 24.7 ± 2.0y; 13 female, 22.5 ± 3.6y) were seated in a dynamometer with their right hip and knee angle set to 110° and 140°, respectively, with an ankle excursion set between 0° and 40° plantar flexion (PF). MVC torque, peak twitch torque, and prolonged low frequency force depression were used to assess eccentric exercise-induced neuromuscular impairments. History-dependent contractions consisted of a 1 s isometric (40°PF or 0°PF) phase, a 1 s shortening or lengthening phase (40°/s), and an 8 s isometric (0°PF or 40°PF) phase.
RESULTS: Following eccentric exercise; MVC torque was decreased, prolonged low frequency force depression was present, and both rFE and rFD increased for all maximal and submaximal conditions.
CONCLUSIONS: The history dependence of force during voluntary torque and activation matching, and electrically stimulated contractions is amplified following eccentric exercise. It appears that a weakened neuromuscular system amplifies the magnitude of the history-dependence of force.