Qualitative and Quantitative Evaluation of Muscle Fatigue by Muscle Stiffness

本研究的目的是测量和估计肌肉疲劳，利用肌肉粘弹性的变化，坐在一个车辆座椅上很长一段时间，这是从生物力学阻抗谱计算。这项研究涉及肌肉疲劳的变化，这是暂时的，而不是慢性的。的EMG为了分析由坐在车辆座椅上的不良姿势引起的肌肉应变和肌肉疲劳之间的关系，还测量了在肌肉疲劳中频谱的中值频率降低的肌电（肌电图）和由皮肤表面的长时间接触引起的下背部充血的血流量。1994年，（1）确定了测量点，其易于发生肌肉僵硬度的变化和（2）测量血流量。1995年，（3）肌肉粘弹性的计算和（4）肌电的测量，明确了肌肉应变与不良姿势引起的疲劳之间的关系。结果表明：（1）长时间坐在较差的汽车座椅上测量下背部的生物力学阻抗时，在第3、4腰椎之间、第4、5腰椎之间脊柱左右40mm处肌肉粘弹性发生变化。(2)腰部皮肤与座椅接触引起的血液流动轻微变化。(3)由机械阻抗谱计算的粘性和弹性随着肌肉疲劳而增加。(4)针对肌肉疲劳时肌电积分值增加、频谱中位频率降低的现象，利用主成分分析法，结合实测的粘弹性和肌电，对肌肉疲劳进行了估计，提出了一种新的客观的肌肉疲劳指标。该指数表明，一个适当的相关性与主观疲劳发生在下背部坐在标准和较差的车辆座椅上很长一段时间。

The purpose of this study is to measure and estimate muscle fatigue utilizing muscle viscoelasticity change by sitting on a vehicle seat for a long period of time, which is calculated from the biomechanical impedance spectrum. This study deals with a change in muscle fatigue which is transitory, not chronic. An EMG (electromyogram), whose median frequency of spectrum decreases in muscle fatigue and a blood flow, with which a low back is congested, caused by a long time contact of skin surface are also measured in order to analyze the relation between muscle strain and muscle fatigue caused by a worse posture sitting on a vehicle seat.In 1994, (1) measuring points were determined, which were apt to occur a change of muscle stiffness and (2) blood flow was measured. In 1995, (3) calculation of viscoelasticity of muscle and (4) EMG were measured, and the relation between muscle strain and fatigue caused by a worse posture was made clear. The summary is as follows : (1) muscle viscoelasticity changes around 40mm away from the right and left side of the spinal column between the 3rd and the 4th lumbar vertebra, and between the 4th and the 5th lumbar vertebra, when the biomechanical impedance of low back is measured by sitting on a worse vehicle seat for a long period of time. (2) blood flow changes slightly caused by a skin contact with seat in low back. (3) viscosity and elasticity, calculated from the mechanical impedance spectrum, increase with muscle fatigue. (4) integrated value of EMG increases and median frequency of EMG spectrum decreases in muscle fatigue.Muscle fatigue was estimated by using Principle Component Analysis with the measured viscoelasticity and EMG,and a new objective muscle fatigue index was proposed. The index suggested an adequate correlation with a subjective fatigue which occurred in low back by sitting on standard and worse vehicle seat for a long period of time.