The quantification of muscle fatigue is a very important subject in the field of orthopedics, rehabilitation, human science and so on. This paper describes a quantification and subjective estimation of muscle fatigues. Among various causes of the muscle fatigue, the authors take note of changes in muscle stiffness. The elasticity (μ_1) and viscosity (μ_2) of muscle are measured on the low back, in order to estimate the muscle stiffness changes caused by sitting on the vehicle seat for a long time. The viscoelasticity is obtained from the response of the random vibration applied on the skin surface. Moreover MNF (Median Frequency) and IEMG (Integrated EMG) are calculated from EMG wave form. The subject sits on the standard seat and the worse seat apt to cause the muscle fatigue. The authors propose the objective muscle fatigue index based on the PCA (Principal Component Analysis) of the differences of the muscle stiffness and EMG between the standard seat and the worse seat.

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As many effort has been made to increase the opportunity of the social participant of the individuals with mental retardation in modern society, the contact between the individuals with mental retardation and the society will increase more and more. When the individuals with mental retardation lead the social life, the one of the most important physical factor is total body endurance. So it is important that we secure the probability of improving the total body endurance performance precisely. We are used to measure the record of 1500m run for the indicator of endurance performance. But it is very hard to measure for the individuals with mental retardation. So we try to estimate the record from other physical factor. Generally the multiple regression are used to apply such the estimation, but for the individuals with mental retardation, multiple regression isn't available bccause their data distribution does not fit the normal distribution and their understanding of the measuring method is different each measuring time. So we propose the method which can estimate the record of 1500m run. This method use Liner Probability Regression, which based on the Fuzzy Theory. The Fuzzy Theory is proposed from L. A. Zadeh in 1965. This theory use membership function instead of population value. The subjects consisted of 20 individuals with mental retardation aged 32.7±11.0. The test items were Standing trunk flexion, Trunk extension, Closed-eyes foot balance, Grip strength(R,L), Back strength. Standing long jump, Soft ball throw, Shuttle run, 50m run, Sit ups and 1500m run. The result were as follows: ・The method using probability liner regression could estimate the range of the record of 1500m run. ・The method using probability liner regression could numerically set the object of improving performance. ・The estimated range which was set "the improving probability of performance" was very valid range.

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