Final answer:
Motor units are recruited asynchronously to prevent muscle fatigue and increase endurance, with synchronous recruitment occurring during high-force tasks such as heavy lifting. Fine motor control tasks like eye movement depend on small motor units for precise action.
Step-by-step explanation:
We recruit motor units asynchronously to prevent complete muscle fatigue, allowing some motor units to rest while others are active. This enhances endurance and allows for longer muscle contractions. Synchronous motor unit recruitment is reserved for instances where maximal force is required, such as in heavy lifting or power movements.
For example, when performing a heavy squat, the large motor units of the thigh muscles are recruited synchronously to generate the great force needed to lift the weights. These large motor units are capable of powerful gross movements by controlling thousands of muscle fibers with a single motor neuron.
However, asynchronous recruitment is advantageous for endurance and control, as seen with the small motor units in the extraocular muscles of the eye. These smaller units provide precise and fine motor control, essential for delicate tasks like coordinating eye movements.