Myosin head detachment from actin is triggered by:-

At rest, myosin heads are bound=adenosine diphosphate(are said to be in a "cocked" position)in relation to the thin filament = does not have Ca 2+ bound to = the troponin--tropomyosin complex. Ca 2+ bound to = troponin--tropomyosin complex induces = conformational change in the thin filament = that allows for myosin heads to cross-bridge with thin filament actin. Myosin heads rotate = move the attached actin and shoen the muscle fiber = forming power stroke. At the end of power stroke = ATP binds = exposed site = causes = detachment = from actin filament. ATP is hydrolyzed = into ADP and inorganic phosphate (P i ). This chemical energy is used to "re-cock" the myosin head.