Stepwise sarcomere shortening: analysis by high-speed cinemicrography.

Sarcomere shortening in striated muscle appears to follow a regionally synchronized staircase-like time course not anticipated in some cross-bridge models. The visualization method used has been criticized as subject to Bragg diffraction effects. Two independent optical methods were used to visualize a muscle during contraction; agreement between the stepwise behavior observed with the two methods suggests that the phenomenon is genuine.