Abstract: An electrodynamograph for determining, in percentage, the degree of fatigue of the human organism following physical or intellectual effort comprises an actuator which is displaced by the subject and is coupled to a mechanical-electrical transducer producing an output which is applied to a recorder through an electronic switch which provides, by interrupting the recordal, indicia of time. An audio-frequency generator produces a signal which is connected periodically to a loudspeaker through another electronic switch, e.g. a multivibrator-controlled relay, to produce acoustic outputs establishing the cadence or rhythm of operation of the actuator. A trace is produced of the exertion of the individual before and after work and the integrals of the respective traces are determined to establish a percentage representing the fatigue of the subject following the physical or intellectual effort.