Historically relevant hypotheses on the pathophysiology of muscle cramp are reviewed. Psychosomatic, static, vascular, myogenic and neural theories are highlighted from a clinician's point of view. Modern neurophysiological research leaves little doubt that true muscle cramp is caused by explosive hyperactivity of motor nerves. Several mechanisms may be involved including spinal disinhibition, abnormal excitability of motor nerve terminals and spreading of muscle contraction by ephaptic transmission or axon reflexes.