An apparatus and method for counting exercise repetitions are provided for accurate counting exercise repetition even when an exerciser attaches the apparatus in different places and along different orientations of his or her body. The apparatus and method utilizing acceleration data along at least three axes and determines a valid step if at least one of the acceleration profiles falls within at least one of said thresholds. Moreover, a method of identifying an optimal axis for exercise repetition measurement is disclosed by comparing the acceleration profiles of previous steps with amplitude, cycle and rhythm thresholds.