An isometric/pacing exercise device that is adaptable to exercise apparatuses to produce a signal to the user to exert an isometric muscular force against the force provided by the exercise apparatus. The signal can be either aural or visual. The isometric/pacing exercise device provides a convenient means for a user to isometrically exercise their muscles on existing exercise apparatuses which do not presently have such a signaling device. The device is adaptable to most exercise apparatuses.