The central nervous system has two distinct ways of controlling
the force produced by a muscle through motor unit recruitment. They
are
- spatial recruitment
- temporal recruitment
- Spatial recruitment is the activation of more motor units to
produce a greater force. Larger motor units contract along with
small motor units until all muscle fibers in a single muscle are
activated, thus producing the maximum force.
- Temporal motor unit recruitment or rate coding, deals with the
frequency of activation of muscle contractions. Consecutive
stimulation on the motor unit fibers from the alpha motor neuron,
causes the muscle to twitch more frequently until the twitches
"fuse" temporally. This produces a greater force than singular
contractions by decreasing the interval between stimulations to
produce a larger force with the same number of motor units.