Figure 8. Myofibrillar model for increased cross-bridge kinetics at short sarcomere length.

A, representation of sarcomeric proteins at long sarcomere length. Titin is extended and provides passive tension that may help maintain extension of MyBP-C from the thick filament to provide constraint on the myosin crossbridge. B, at short sarcomere length, titin is slack and this decrease in passive tension may alleviate MyBP-C constraint of the crossbridge, which (perhaps to a greater extent in α-MyHC thick filaments) may lead to more flexible crossbridges, which may have faster turnover kinetics and/or more readily activate the thin filament.