Recently, many people do some exercises regularly to keep good shape. When they do some exercises, many people evaluate their physical condition subjectively. However, subjective assessment is confusion. Therefore, it is necessity to estimate body condition objectively. There are many ways to estimate body condition. Among them, in this study we estimate from muscle fatigue. Muscles are moved by muscle fibers contracting after receiving commands from the brain. People can move muscles freely, but they cannot keep moving them infinity. If muscle fatigue occurs, a person can begin to lose coordination. As a consequence, it is difficult to train efficiently and the decrease or output has the potential to facilitate serious injury. Therefore, understanding muscle fatigue is vital information when building muscular strength or endurance in exercises. Most of exercises are composed contracting plural muscles. In a previous study, during low level contraction a electromyogram (EMG) recordings confirmed that alternating recruitment of various parts of the knee-extensors to delay fatigue. When tiredness was caused at the movement composed by two or more muscles, each muscles are observed the activity alternation. In this study, we make a hypothesis about continuing to exert tension to alternate muscle activity in the exercise consisting of multiple muscles. If muscles become fatigue gradually, frequency of alternate muscle activity increase, and finally exhausted, all the muscles contract synchronously. Accordingly, EMG signals pattern and rate of power synchronous. © 2011 IEEE.