Phase-Locked Loop Measurement of Sarcomere Length with High Time Resolution

A method for making high-speed measurements of sarcomere length directly from the muscle striation image is presented. A phase-locked loop is used with a self-scanned photodiode array to measure the spatial frequency of the striation pattern. Computation circuitry converts frequency to sarcomere length. The sarcomere length output has a resolution better than 2 nm at a sample rate of once every 250¿s.