Each myosin head independently attaches to a binding site on the actin filament, pivots through its power stroke while pulling the actin along, then detaches and resets to attach further along. The scene shows this cycle for every head at once.
- Gold — idle, searching for a binding site.
- Green — attached and mid power-stroke.
- Red flash — forced off before finishing the stroke because the filament slid past too fast.
The time a head has to complete a stroke before the filament slides away is fixed by chemistry. At low velocity there is time to spare, so many heads stay attached at once and force is high. At high velocity that window shrinks, more heads are torn off mid-stroke, and fewer stay attached simultaneously — so force falls. This trade-off is the muscle's force–velocity relationship, plotted live on the right.