Final answer:
Motor unit discharge behavior controls muscle force via recruitment, allowing for increased muscle contraction strength as greater force is needed. This is combined with a graded response and the length-tension relationship affecting force production. Neural control manages this process, preventing fatigue by alternating activity among motor units.
Step-by-step explanation:
The discharge behavior of motor units affects the control of force produced by a muscle through a process called recruitment. This neural control mechanism allows for fine-tuned muscle contraction in response to the demands placed on the muscle. Small, lower-threshold motor units are activated first, producing minimal force. However, as more strength is required, larger motor units with higher-threshold motor neurons are recruited to activate larger muscle fibers, thereby increasing the overall muscle contraction. This recruitment leads to a graded muscle response, further refined by the frequency of action potentials impacting muscle tension. Additionally, muscle activity is influenced by the length-tension relationship, with optimal force produced when sarcomeres are at their ideal length for cross-bridge formation.
Furthermore, neural control regulates various types of muscle contractions, including concentric, eccentric, and isometric contractions, all under the control of motor units. Given the energy requirements to sustain contraction and to prevent complete muscle fatigue, not all motor units are simultaneously active at any given time. Instead, some motor units rest while others remain active, facilitating prolonged muscle activity.