GLOSSARY

The power stroke is the step of the cross-bridge cycle in which the actin-bound myosin head pivots and pulls the actin filament towards the sarcomere centre; this is the moment of mechanical force production.

Molecular Mechanism

• Before the stroke: the myosin head, carrying ADP and phosphate, binds to actin in a high-energy state.
• Phosphate release: triggers the power stroke.
• Lever-arm rotation: the myosin neck swings like an oar by about 45–70 degrees, moving actin by about 5–10 nanometres.
• ADP release: at the end of the stroke, the myosin head is tightly bound to actin in the rigor state until a new ATP binds.

Force per Stroke