Device (1) for measuring muscular capacity, comprising: removable fastening means (12) for fastening the device to the athlete or to the moved weight (3; 2); autonomous electrical power supply means (15); a display (11); a three-axis accelerometer (14) for delivering a sequence of accelerations (a(t)) along the axis of movement of the weight, said sequence comprising at least 100 measurements per second over a duration between 1 and 10 seconds; and data processing means (16) for determining, at the end of the test, on the basis of said sequence of accelerations, at least one quantity representative of the muscular capacity of the athlete and for displaying this quantity on said display (11).