Which statement best describes how motor unit recruitment and training interact to influence exercise performance?

• A. More motor units are recruited as force demands increase; training improves synchronization and rate coding, enhancing force production and efficiency.
• B. Training reduces the number of motor units recruited for all tasks.
• C. Motor unit recruitment is fixed regardless of force.
• D. Only type I fibers are recruited for all efforts.

Answer: (A)

The main idea being tested is how the nervous system recruits muscle fibers and how training changes that process to boost performance. When more force is needed, the nervous system activates more motor units, including higher-threshold fast-twitch units, in line with the size principle. Training enhances the neural aspects of this control: firing rates (rate coding) increase, motor units fire more in a coordinated, synchronized pattern, and the system becomes more efficient at bringing in the necessary units for a given task. This combination means you can produce greater force and do so more efficiently, especially under heavy loads or rapid movements. The other statements don’t fit because recruitment isn’t fixed, training doesn’t universally reduce the number of motor units used for all tasks, and not only type I fibers are recruited for all efforts.