Qualitative and Quantitative Evaluation of Muscle Fatigue by Muscle Stiffness

本研究的目的是利用长时间坐在汽车座椅上的肌肉粘弹性变化来测量和估计肌肉疲劳，这是由生物力学阻抗谱计算得出的。这项研究涉及肌肉疲劳的变化是短暂的，而不是慢性的。我们还测量了由于长时间接触皮肤表面引起的肌疲劳时肌电图（EMG）的频谱中位数频率下降，以及腰背充血时的血流，分析了不良坐姿引起的肌肉劳损与肌肉疲劳之间的关系。1994年，(1)确定了容易发生肌肉僵硬变化的测点；(2)测量了血流量。1995年，(3)计算了肌肉的粘弹性，(4)测量了肌电图，明确了不良姿势引起的肌肉劳损与疲劳之间的关系。综上所述：(1)长时间坐在较差的汽车座椅上测量腰背生物力学阻抗时，第3 ~ 4腰椎、第4 ~ 5腰椎之间距离脊柱左右两侧约40mm处肌肉粘弹性发生变化。(2)下背部皮肤与座椅接触，血流稍有变化。(3)黏度和弹性，由机械阻抗谱计算，随肌肉疲劳而增加。(4)肌肉疲劳时肌电综合值升高，肌电谱中位数频率降低。利用主成分分析法，结合肌电图和粘弹性测量值对肌肉疲劳进行了估计，提出了一种新的客观肌肉疲劳指标。该指数表明，由于长时间坐在标准和较差的汽车座椅上，腰背部发生的主观疲劳与该指数有充分的相关性。

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.