This study explored the relationship between single motor unit (MU) firing rates (FRs) and limb movement velocity during voluntary shortening contractions when accounting for the effects of time course variability between different kinematic comparisons. Single MU trains recorded by intramuscular electromyography in agonist muscles of the anconeus (n = 15 participants) and lateral head of the triceps brachii (n = 6) were measured during each voluntary shortening contraction. Elbow extension movements consisted of a targeted velocity occurring along the sagittal plane at 25, 50, 75 and 100% of maximum velocity. To account for the effect of differences in contraction time course between parameters, each MU potential was time locked throughout the shortening muscle contraction and linked with separated kinematic parameters of the elbow joint. Across targeted movement velocities, instantaneous FRs were significantly correlated with elbow extension rate of torque development (r = 0.45) and torque (r = 0.40), but FRs were not correlated with velocity (r = 0.03, p = n.s.). Instead, FRs had a weak indirect relationship with limb movement velocity and position assessed through multiple correlation of the stepwise kinematic progression. Results show that voluntary descending synaptic inputs correspond to a more direct relationship between agonist muscle FRs and torque during shortening contractions, but not velocity. Instead, FRs were indirectly correlated to preparing the magnitude of imminent movement velocity of the lagging limb through torque.

本研究在考虑不同运动学比较之间的时间过程变异性影响时，探讨了在自主缩短收缩期间单运动单元 (MU) 放电率 (FR) 与肢体运动速度之间的关系。通过肌内肌电图记录肘节激动肌（n  = 15 名参与者）和肱三头肌外侧头（n = 6) 在每次自愿缩短收缩期间测量。肘部伸展运动包括沿矢状面以最大速度的 25%、50%、75% 和 100% 发生的目标速度。为了解释参数之间收缩时间过程差异的影响，每个 MU 电位在整个缩短肌肉收缩过程中都被时间锁定，并与肘关节的独立运动学参数相关联。在目标运动速度中，瞬时 FR 与扭矩发展的肘部伸展率 ( r  = 0.45) 和扭矩 ( r  = 0.40)显着相关，但 FR 与速度无关 ( r  = 0.03, p = ns)。相反，FRs 与肢体运动速度和位置的间接关系是通过逐步运动学进程的多重相关性评估的。结果表明，在缩短收缩过程中，自主下降突触输入对应于激动肌 FR 和扭矩之间更直接的关系，但与速度无关。相反，FR 与通过扭矩准备滞后肢体即将发生的运动速度的大小间接相关。