Question

Generally, muscle force is greater when which of the following occur?

A) More motor units are involved in a contraction

B) More calcium is involved in a contraction

C) There is a greater percentage of slow-twitch fibers in the muscle

D) A person has hypermobile joints

Answer 1

A-->More motor units are involved in a contraction

Motor unit recruitment refers to the activation of additional motor units to accomplish an increase in contractile strength
in a muscle. A motor unit consists of one motor neuron and all of the muscle fibers it stimulates. All muscles consist of a
number of motor units and the fibers belonging to a motor unit are dispersed and intermingle amongst fibers of other units.
The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the
number of fibers and size of the muscle.When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a weak but distributed muscle contraction.
The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction.
Motor unit recruitment is a measure of how many motor neurons are activated in a particular muscle, and therefore is a measure of how
many muscle fibers of that muscle are activated. The higher the recruitment the stronger the muscle contraction will be.
Motor units are generally recruited in order of smallest to largest (smallest motor neurons to largest motor neurons, and thus slow to fast twitch) as contraction increases.