Department of Life Sciences, University of Roehampton, London SW15 4JD, UK
School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough LE11 3TU, Leicestershire, UK.
J Exp Biol. 2018 Dec 10;221(Pt 24):jeb193367. doi: 10.1242/jeb.193367.
This study investigated the influence of contraction speed and type on the human ability to rapidly increase torque and utilise the available maximum voluntary torque (MVT) as well as the neuromuscular mechanisms underpinning any effects. Fifteen young, healthy males completed explosive voluntary knee extensions in five conditions: isometric (ISO), and both concentric and eccentric at two constant accelerations of 500 deg s (CON and ECC) and 2000 deg s (CON and ECC). Explosive torque and quadriceps EMG were recorded every 25 ms up to 150 ms from their respective onsets and normalised to the available MVT and EMG at MVT, respectively, specific to that joint angle and velocity. Neural efficacy (explosive voluntary:evoked octet torque) was also measured, and torque data were entered into a Hill-type muscle model to estimate muscle performance. Explosive torques normalised to MVT (and normalised muscle forces) were greatest in the concentric followed by the isometric and eccentric conditions, and in the fast compared with slow speeds within the same contraction type (CON>CON>ISO, and ECC>ECC). Normalised explosive-phase EMG and neural efficacy were greatest in concentric conditions, followed by isometric and eccentric conditions, but were similar for fast and slow contractions of the same type. Thus, distinct neuromuscular activation appeared to explain the effect of contraction type but not speed on normalised explosive torque, suggesting the speed effect is an intrinsic contractile property. These results provide novel evidence that the ability to rapidly increase torque/force and utilise the available MVT is influenced by both contraction type and speed, owing to neural and contractile mechanisms, respectively.
本研究旨在探讨收缩速度和类型对人体快速增加扭矩的能力以及利用可用最大自主扭矩（MVT）的影响，以及支撑这些影响的神经肌肉机制。15 名年轻健康的男性在五种条件下完成了爆发性的膝关节伸展：等长（ISO）以及两种恒加速度（500°/s 和 2000°/s）的向心和离心收缩（CON 和 ECC）。在各自起始后的 150ms 内，每隔 25ms 记录爆发性扭矩和股四头肌肌电图，并分别归一化为相应关节角度和速度下的可用 MVT 和 EMG。还测量了神经效率（爆发性自主：诱发八重肌扭矩），并将扭矩数据输入 Hill 型肌肉模型，以估计肌肉性能。归一化到 MVT 的爆发性扭矩（和归一化的肌肉力）在向心收缩中最大，其次是等长收缩和离心收缩，在相同收缩类型中，快速收缩比慢速收缩更大（CON>CON>ISO，ECC>ECC）。在向心收缩条件下，归一化的爆发性肌电图和神经效率最大，其次是等长收缩和离心收缩，但对于相同类型的快速和慢速收缩，两者相似。因此，明显的神经肌肉激活似乎解释了收缩类型对归一化爆发性扭矩的影响，但不能解释速度的影响，这表明速度的影响是一种内在的收缩特性。这些结果提供了新的证据，表明快速增加扭矩/力和利用可用 MVT 的能力受到收缩类型和速度的影响，这分别归因于神经和收缩机制。
