Fig 3. Myosin S1 consisting of a heavy chain, ELC (blue), and RLC (yellow) performing a powerstroke with a lever-arm rotation while strongly actin bound.

The arc subtended by, Φ, the angle a single lever-arm helix rotates in sequential images defines a sequence of chords on a circle of diameter L equal to the lever-arm length indicated. Chord length is step-size, d, given by Eq 3. The ELC N-terminal extension, shown actin bound at the end of the powerstroke, plays a major role in the proposed mechanism for strain sensing in the myosin.