A chemical complex formed between myosin and actin during a muscle action. In the rigor complex, the myosin head is bent to the 45° position and is bound to actin. Unbinding of the head requires ATP and removal of calcium bound to troponin so that tropomyosin can prevent the myosin head from binding to the actin. Muscle cramps may be due to the development of a rigor complex, either because of lack of ATP or an inability to remove calcium. See also sliding-filament theory.
Subjects: Sports and Exercise Medicine.