Transcutaneous neuromuscular electrical stimulation (NMES) can be used to activate the quadriceps femoris muscle to produce knee extension torque via seven distinct motor points, defined as the most sensitive locations on the muscle belly to electrical stimuli. However, it remains unclear how much individual motor points of the quadriceps femoris muscle contribute to the knee joint torque. Here we systematically investigated the contribution of each motor point of the quadriceps femoris muscle to the knee joint torque produced by paired electrical stimuli. Ten able-bodied individuals participated in this study. Paired electrical stimuli was applied by delivering electrical impulses on the motor points in all combinations among seven motor points (i.e., totaling to 127 combinations) at two different stimulation intensities (i.e., 25% and 50% of the maximum) while recording isometric knee joint torque. The contribution of individual motor points was estimated using statistical analyses. We found that a linear addition of twitch torques induced by single motor point stimulus overestimated the twitch torques induced by multiple motor point stimulations, suggesting overlaps in muscle fibres activated by each motor point. Using multiple linear regressions, we identified the average contribution of each motor point to the knee extension torque during paired electrical stimuli and found significant differences between these torque contributions. We demonstrated that seven distinct motor points can be activated for the quadriceps muscle group using paired electrical stimuli and identified the contribution of each motor point to knee extension torque during twitch muscle contraction; these findings provide useful information to design rehabilitation using NMES on quadriceps femoris muscles.

中文翻译：

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神经肌肉电刺激过程中股四头肌各运动点对膝关节伸展力矩的贡献


经皮神经肌肉电刺激 (NMES) 可用于激活股四头肌，通过七个不同的运动点（定义为肌腹上对电刺激最敏感的位置）产生膝关节伸展扭矩。然而，目前尚不清楚股四头肌的各个运动点对膝关节扭矩的贡献有多大。在这里，我们系统地研究了股四头肌的每个运动点对成对电刺激产生的膝关节扭矩的贡献。十名身体健全的人参与了这项研究。通过以两种不同的刺激强度（即最大值的25%和50%）在七个运动点（即总共127个组合）的所有组合中的运动点上传递电脉冲来施加成对电刺激，同时记录等长膝关节扭矩。使用统计分析来估计各个运动点的贡献。我们发现，单个运动点刺激引起的抽搐扭矩的线性相加高估了多个运动点刺激引起的抽搐扭矩，这表明每个运动点激活的肌纤维存在重叠。使用多元线性回归，我们确定了配对电刺激期间每个运动点对膝关节伸展扭矩的平均贡献，并发现这些扭矩贡献之间存在显着差异。 我们证明了使用成对的电刺激可以激活股四头肌群的七个不同的运动点，并确定了抽搐肌肉收缩期间每个运动点对膝关节伸展扭矩的贡献；这些发现为利用 NMES 对股四头肌进行康复设计提供了有用的信息。