Final answer:
Recruitment is the process of activating additional motor units to produce a stronger muscle contraction.
Step-by-step explanation:
When additional motor units are activated to produce a stronger muscle contraction, the process is known as recruitment. Recruitment is the increase in the number of motor units involved in a muscle contraction. By recruiting more motor units, the muscle contraction grows progressively stronger. This mechanism allows the nervous system to efficiently utilize the skeletal muscle.