Before revision:  Consistent with previous work, we find that the duration of actin engagement and average force are highly sensitive to changes in ensemble size(Nheads) , motor duty ratio (dr), and environmental stiffness(k). Catch-bond kineticsshared by myosin II isoforms sharpen this sensitivity through positive feedback such that increases in Nheads, dr, or k above threshold values drive a rapid transition from non-processive to processive engagement. Tuning motor parameters to match different myosinII isoforms suggest that myosin filaments are poised to respond sharply to environmental stiffness or externally applied force. Thus, force production by myosin filaments is subject to switch-like control via tunable internal properties or mechanical context.
After revision:  Consistent with previous work, we find that the duration of actin engagement and average force are highly sensitive to changes in ensemble size(Nheads) , motor duty ratio , and external load, and that of force build up, which scaled with ensemble stall force, gliding speed, and load stiffness. While such regulation did not require force-dependent kinetics, the myosin catch bond produced positive feedback between attachment time and force to trigger switch-like control via tunable internal properties or mechanical context.