This paper proposes a method of surface electromyography (sEMG)‐based mensuration of muscle fatigue during elbow flexionextension. The proposed method has two parts. First, the joint angle and locations of body segments are estimated using inertial measurement units (IMU) and the OpenSim biomechanics simulator. Second, muscle fatigue is measured using OpenSim and a three‐compartment muscle fatigue model. The experimental results show that muscle fatigue increases in accordance with the momentum.