Non-invasive estimation for the muscle fiber composition by mechanomyogram

在短暂的最大自愿收缩（MVC）后的抽搐力增强被称为激活后增强（PAP）。PAP可能是估计纤维类型分布的有用工具，因为它在快抽动纤维中比在慢抽动纤维中更明显。然而，无法测量躯干肌肉（如竖脊肌）和协同肌肉（其力输出受不同肌肉的影响）的力输出。肌力图（MMG）更有选择性地反映单个肌肉的机械活动，其振幅与抽搐收缩力线性相关。因此，建议MMG能够比力输出更直接地测量收缩特性。本研究的目的是阐明MMG测定PAP的有效性和估计肌纤维成分的可能性。在健康受试者的腓肠肌（GAS）和比目鱼肌（SOL）分别通过胫骨神经和每块肌肉表面进行10s-MVC足底屈曲前后的电刺激。PAP定义为短暂MVC前后MMG和抽搐力的振幅变化。在MMG和抽动力共同作用下，GAS的PAP大于SOL。与抽动力相比，MMG在两块肌肉之间的PAP表现出更大的差异。在胫骨神经刺激试验中，MMG显示GAS组的PAP明显大于SOL组。为了阐明MMG测定的PAP是否可以作为肌病的诊断指标，我们还检查了肱二头肌的PAP。患者的PAP与肌肉活检检查一致。这些结果表明，MMG测定的PAP是估计肌纤维成分的有效工具。

The potentiation of twitch force after a brief maximal voluntary contraction (MVC) is referred to as the post-activation potentiation (PAP). The PAP may be a useful tool to estimate the fiber type distribution since it is more pronounced in fast twitch fibers than that in slow twitch fibers. However, the force output is unable to be measured from trunk muscles such as erector spine and from synergistic muscles of which the force output is affected by different muscles. The mechanomyogram (MMG) reflects more selectively the mechanical activity of individual muscles and its amplitude is linearly related to the twitch contraction force. Thus, it is suggested that the MMG enables more direct measure of the contractile properties than the force output. The purpose of this study was to clarify the availability of the PAP determination by the MMG and the possibility for the estimation of muscle fiber composition. In healthy subjects, gastrocnemius (GAS) and soleus (SOL) muscles were electrically stimulated before and after 10s-MVC of plantar flexion through tibial nerve and on the surface of each muscle, respectively. The PAP was defined as amplitude change in both the MMG and twitch force induced before and after the brief MVC. The PAP in GAS was greater than that in SOL when determined not only by the MMG and but also by the twitch force. The MMG represented greater difference in the PAP between the two muscles compared with the twitch force. In tibial nerve stimulation test, the MMG demonstrated that the PAP in GAS was significantly greater than that in SOL. In order to elucidate whether the PAP determined by the MMG can be used as a diagnostic index for the myopathies, the PAP in biceps brachii muscles was also examined. The PAP in the patients was consistent with the examination of the muscle biopsy. These results suggest that the PAP determined by the MMG is an effective tool for the estimation of muscle fiber composition.