Which of the following terms describes when a motor unit receives more than one stimulus?

The correct term that describes when a motor unit receives more than one stimulus is summation. This occurs when successive stimuli are applied to a muscle fiber before it has a chance to relax completely. As a result, the tension produced by the muscle increases, leading to a stronger contraction. This process is crucial for muscle performance because it enables finer control over muscle contractions and allows the muscle to generate more force when needed.

In the context of muscle physiology, summation can be broken down into two types: temporal summation, where stimuli are delivered in close succession, and spatial summation, where multiple motor units are recruited to increase contraction strength. The concept of summation is fundamental for understanding how muscles respond to varying levels of demand, whether in a controlled environment like exercise or in everyday activities.

This understanding also highlights the importance of appropriate stimulus frequency and recruitment of motor units in effectively training muscle strength and endurance.