Question

what does force regulation in a given muscle depend on (other than Cross-Bride formation)

Answer 1

Fore regulated in a given muscle is also depends on motor unit recruitment, so the force of muscle contraction is controlled by multiple motor unit summation or recruitment.

A motor unit consists of the motor neuron and the grouping of muscle fibers innervated by the neuron, There are often multiple sizes of motor unit within a motor pool, a smaller motor unit will be capable for generating precise movement, while large motor unit may employed to generate larger force, For example, a small motor unit in the biceps can be activated for small precise movements, while a larger motor unit in a thigh muscle can be activated to facilitate more forceful actions. The central nervous system is responsible for the orderly recruitment of motor neurons,  motor units are recruited from smallest to largest based on the size of the load. For smaller loads requiring less force, slow twitch, low-force, fatigue-resistant muscle fibers are activated prior to the recruitment of the fast twitch, high-force, less fatigue-resistant muscle fibers. Larger motor units are typically composed of faster muscle fibers that generate higher forces.

Therfe are two ways by which force prodution can be controled by a muscle through motor recruitment, Spatial recriuitment and temporal recruitment., Spatial recruitment is the activation of more motor units to produce a greater force. while in temporal summation a single presynaptic neuron fires many times in sucession causing the post synaptic neuron to reach its threshold and fire

The force a muscle generates is dependent on the length of the muscle and its shortening velocity. muscles generate the greatest force when at their resting (ideal) length, and the least amount of force when shortened or stretched relative to the resting length.

The shortening velocity affects the amount of force generated by a muscle,The shortening velocity is the speed at which a muscle changes length during a contraction. The force of a muscle contraction declines with increasing velocity. for eg, Twitch contractions, which are short in duration, do not reach peak force.Tetanic contractions, which are long in duration, reach peak force and plateau.