A method for exercising one or more muscles of the body wherein one or more muscle(s) are contracted to move a limb through a range of motion in opposition to an oscillating resistive force. During a muscular contraction, the direction and/or the magnitude of the resistive force changes in an oscillatory fashion thereby inducing perturbations in the musculature. The oscillations in the magnitude and/or the direction of the resistive force include a plurality of cycles during a single repetition of muscular contraction. The waveform and frequency of the oscillations may vary during a repetition or remain constant. Embodiments of devices providing an oscillatory resistive force are presented. The embodiments provide means for enabling an exerciser to perform resistance-type exercises in accordance with the method. A guided spherical bearing may be used for rotating a lead pulley or a rigid arm to create lateral resistive force oscillations. Non-circular lead pulleys may be used to fluctuate the resistive force magnitude. The oscillations in magnitude and/or direction of the resistive force may be periodic or randomized such that during subsequent repetitions the oscillations occur at differing points.