Department of Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada.
Appl Physiol Nutr Metab. 2019 Mar;44(3):301-308. doi: 10.1139/apnm-2018-0104. Epub 2018 Sep 6.
Muscle length and preceding activity independently influence rate of torque development (RTD) and electromechanical delay (EMD), but it is unclear whether these parameters interact to optimize RTD and EMD. The purpose of this study was to determine the influence of muscle length and preceding activity on RTD and EMD during voluntary and electrically stimulated (e-stim) contractions. Participants (n = 17, males, 24 ± 3 years) performed isometric knee extensions on a dynamometer. Explosive maximal contractions were performed at 2 knee angles (35° and 100° referenced to a 0° straight leg) without preceding activity (unloaded, UNL) and with preceding activities of 20%, 40%, 60%, and 80% of maximal voluntary contraction (MVC) torque. Absolute and normalized voluntary RTD were slowed with preceding activities ≥40% MVC for long muscle lengths and all preceding activities for short muscle lengths compared with UNL (p < 0.001). Absolute and normalized e-stim RTD were slower with preceding activities ≥40% MVC compared with UNL (p < 0.001) for both muscle lengths. Normalized RTD was faster at short muscle lengths than at long muscle lengths (p < 0.001) for e-stim (∼50%) and voluntary (∼32%) UNL contractions, but this effect was not present for absolute RTD. Muscle length did not affect EMD (p > 0.05). EMD was shorter at 80% MVC compared with UNL (∼35%; p < 0.001) for both muscle lengths during voluntary but not e-stim contractions. While RTD is limited by preceding activity at both muscle lengths, long muscle lengths require greater preceding activity to limit RTD than short muscle lengths, which indicates long muscle lengths may offer a "protective effect" for RTD against preceding activity.
肌肉长度和先前的活动独立地影响扭矩发展速率（RTD）和机电延迟（EMD），但尚不清楚这些参数是否相互作用以优化 RTD 和 EMD。本研究的目的是确定肌肉长度和先前的活动对自愿和电刺激（e-stim）收缩期间 RTD 和 EMD 的影响。参与者（n = 17，男性，24 ± 3 岁）在测力计上进行等长膝关节伸展运动。在没有先前活动（空载，UNL）和先前活动为 20%、40%、60%和 80%最大自愿收缩（MVC）扭矩的情况下，在 2 个膝关节角度（相对于 0°直腿的 35°和 100°）进行爆发性最大收缩。与 UNL 相比，长肌肉长度下的所有先前活动和短肌肉长度下的≥40%MVC 的先前活动都使绝对和归一化自愿 RTD 减慢（p < 0.001）。与 UNL 相比，两种肌肉长度下的≥40%MVC 的绝对和归一化 e-stim RTD 都较慢（p < 0.001）。与 e-stim（约 50%）和自愿（约 32%）UNL 收缩的长肌肉长度相比，短肌肉长度下的归一化 RTD 更快（p < 0.001），但这种效应在绝对 RTD 中不存在。肌肉长度对 EMD 没有影响（p > 0.05）。与 UNL 相比，两种肌肉长度下的 80%MVC 时 EMD 较短（约 35%；p < 0.001），但在 e-stim 收缩时并非如此。虽然 RTD 在两种肌肉长度下都受到先前活动的限制，但长肌肉长度需要更大的先前活动来限制 RTD，而短肌肉长度则不需要，这表明长肌肉长度可能对 RTD 提供一种针对先前活动的“保护作用”。
