Myosin remains strong as muscle contracts

Amuscle held at fixed length under a heavy load will contract rapidly if that load is suddenly decreased, reducing the force the muscle exerts as its velocity increases. During this contraction, what happens within the muscle fiber? According to the prevailing model, all the myosin motors remain attached to actin filaments, and the elasticity of individual myosins accounts for this force reduction—like a rubber band, they pull less as they contract further. New work by Malcolm Irving (King's College, London, UK), Vincenzo Lombardi (University of Florence, Italy), and colleagues now shows that, on the contrary, myosins maintain a constant force during shortening. Fewer, not weaker, myosins reduce the overall muscle force during...