Abstract: A method of and an apparatus for estimating the degrees of the fatigue and pain of muscles and comparing subjects of different weights on the same basis by deriving the variation in the muscular strength such as the dorsal muscular strength, shoulder muscular strength, the grasping power, and the like as an electric signal and integrating the muscular output on one hand, providing an integrated value of the electromyogrammatic amplitude by processing the voltage induced from the muscle to be tested through an electromyogram amplitude and a waveform processor, and by digitally displaying the ratio between these integrated values after correcting the ratio with a weight/muscular strength coefficient.