Pathophysiology
Skeletal muscles work as antagonistic pairs. Contracting one skeletal muscle requires the relaxation of the opposing muscle in the pair. Cramps can occur when muscles are unable to relax properly due to myosin fibers not fully detaching from actin filaments. In skeletal muscle, ATP must attach to the myosin heads for them to disassociate from the actin and allow relaxation — the absence of ATP in sufficient quantities means that the myosin heads remains attached to actin. An attempt to force a muscle cramped in this way to extend (by contracting the opposing muscle) can tear muscle tissue and worsen the pain. The muscle must be allowed to recover (resynthesize ATP), before the myosin fibres can detach and allow the muscle to relax.
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