Force–length relation of skeletal muscles: from sarcomeres to myofibril

Abstract

Sarcomeres are building blocks of skeletal muscles. Given force–length relations of sarcomeres serially connected in a myofibril, the myofibril force–length relation can be uniquely determined. Necessary and sufficient conditions are derived for capability of fully lengthening or completely shortening a myofibril under isometric, eccentric or concentric contraction, and for the myofibril force–length relation to be a continuous single-valued function. Intriguing phenomena such as sarcomere force–length hysteresis and myofibril regularity are investigated and their important roles in determining myofibril force–length relations are explored. The theoretical analysis leads to experimentally verifiable predictions on myofibril force–length relations. For illustration, simulated force–length relations of a myofibril portion consisting of a sarcomere pair are presented.