Contraction of a Myofibril: Partially Contracted Muscle
Contraction of a Myofibril: Completely Contracted Muscle
C alcium and ATP are necessary for myosin cross-bridge cycling with actin filaments.
T ype II, or fast-twitch, muscle fibers are capable of developing higher forces than Type I, or slow-twitch, muscle fibers— especially at higher velocities of muscle action.
T he number of cross-bridges that are attached to actin filaments at any instant in time dictates the force production of a muscle.
Force-Velocity Curve for Eccentric and Concentric Actions
Three Arrangements of Muscle Fibers Fibers parallel to tendon Unipennate muscle Bipennate muscle
M any factors may affect rate of cross-bridge cycling and thus force, including neural activation, calcium concentration, myosin ATPase activity, preloading, prestretch, muscle fiber type and ultrastructure, fatigue through a variety of mechanisms, and number of contractile components (myosin and actin) in parallel.