The activation of additional motor units in a skeletal muscle, in order to increase muscle tension, is called motor unit recruitment.

This statement is true. Motor unit recruitment refers to the process of activating additional motor units within a muscle in order to generate greater force or tension. As the demands placed on a muscle increase, the nervous system will recruit more motor units to help generate the required force. This process allows us to gradually increase the intensity of an activity, like lifting heavier weights or running faster, by recruiting more and more motor units.