Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom.
NeuroMuscularFunction Research Group, School of Exercise and Sport Sciences, Department of Medical Sciences, University of Turin, Turin, Italy.
J Appl Physiol (1985). 2019 Oct 1;127(4):950-958. doi: 10.1152/japplphysiol.00310.2019. Epub 2019 Aug 1.
Conflicting results have been reported on whether closed kinetic chain exercises (such as a leg press) may induce more balanced activation of vastus medialis (VM) and lateralis (VL) muscles compared with open kinetic chain exercise (such as pure knee extension). This study aimed to 1) compare between-vasti motor unit activity and 2) analyze the combined motor unit behavior from both muscles between open and closed kinetic chain exercises. Thirteen participants (four women, mean ± SD age: 27 ± 5 yr) performed isometric knee extension and leg press at 10, 30, 50, 70% of the maximum voluntary torque. High density surface EMG signals were recorded from the VM and VL and motor unit firings were automatically identified by convolutive blind source separation. We estimated the total synaptic input received by the two muscles by analyzing the difference in discharge rate from recruitment to target torque for motor units matched by recruitment threshold. When controlling for recruitment threshold and discharge rate at recruitment, the motor unit discharge rates were higher for knee extension compared with the leg press exercise at 50% [estimate = 1.2 pulses per second (pps), standard error (SE) = 0.3 pps, = 0.0138] and 70% (estimate = 2.0 pps, SE = 0.3 pps, = 0.0001) of maximal torque. However, no difference between the vasti muscles were detected in both exercises. The estimates of synaptic input to the muscles confirmed these results. In conclusion, the estimated synaptic input received by VM and VL was similar within and across exercises. However, both muscles had higher firing rates and estimated synaptic input at the highest torque levels during knee extension. Taken together, the results show that knee-extension is more suitable than leg-press exercise at increasing the concurrent activation of the vasti muscles. There is a significant debate on whether open kinetic chain, single-joint knee extension exercise can influence the individual and combined activity of the vasti muscles compared with closed kinetic chain, multijoint leg press exercise. Here we show that attempting to change the contribution of either the vastus medialis or vastus lateralis via different forms of exercise does not seem to be a viable strategy. However, the adoption of open kinetic chain knee extension induces greater discharge rate and estimated synaptic input to both vasti muscles compared with the leg press.
对于闭链运动（如腿举）是否比开链运动（如纯膝关节伸展）更能引起股直肌（VM）和外侧肌（VL）肌肉的平衡激活，已有相互矛盾的结果报道。本研究旨在 1）比较两种运动单位的活动，以及 2）分析两种肌肉的联合运动单位行为在开链和闭链运动之间的差异。13 名参与者（4 名女性，平均年龄 ± 标准差：27 ± 5 岁）以 10%、30%、50%和 70%的最大自主扭矩进行等长膝关节伸展和腿举。通过卷积盲源分离自动识别 VM 和 VL 的高密度表面肌电图信号和运动单位放电。我们通过分析募集阈值匹配的运动单位从募集到目标扭矩的放电率差异，估计了两块肌肉接收的总突触输入。当控制募集阈值和募集时的放电率时，与腿举运动相比，膝关节伸展运动在 50%[估计值为 1.2 脉冲/秒（pps），标准误差（SE）= 0.3 pps，= 0.0138]和 70%（估计值为 2.0 pps，SE = 0.3 pps，= 0.0001）的最大扭矩时，运动单位的放电率更高。然而，在两种运动中都没有发现股直肌和股外侧肌之间的差异。对肌肉的突触输入的估计证实了这些结果。总之，VM 和 VL 肌肉接收的估计突触输入在运动内和运动间相似。然而，在膝关节伸展运动中，在最高扭矩水平下，两块肌肉的放电率和估计的突触输入都更高。综上所述，结果表明，与腿举运动相比，膝关节伸展运动更适合增加股直肌和股外侧肌的同时激活。关于开链、单关节膝关节伸展运动是否能影响股直肌和股外侧肌的个体和联合活动，与闭链、多关节腿举运动相比，一直存在着很大的争议。在这里，我们表明，试图通过不同形式的运动来改变股直肌或股外侧肌的贡献似乎不是一种可行的策略。然而，与腿举相比，采用开链膝关节伸展运动会引起股直肌和股外侧肌的放电率和估计的突触输入更高。
