A method for measuring exercise level during exercise and for measuring fatigue, in which method electrical signals produced by active muscles are measured with a measuring device and feedback is given from an exercise with a perceivable signal from a feedback device. A device for measuring exercise level and fatigue during exercise, which device includes sensors for measuring electrical signals from active muscles and a feedback device for giving feedback. A momentary exercise level and the level of fatigue of a person are measured or estimated by measuring besides electrical signals received from muscles also other quantities describing exercise and from measuring results one or several indexes are calculated by means of which exercises carried out at different times and under different circumstances are comparable with each other.