AFAA Personal Trainer Certification 2026 – 400 Free Practice Questions to Pass the Exam

A motor unit is defined as a single motor neuron and all the muscle fibers it controls. This is a fundamental concept in exercise physiology and muscle function. The motor neuron transmits signals from the central nervous system to the muscle fibers, causing them to contract. Each motor neuron can innervate multiple muscle fibers, but all those fibers are of the same type. The size of the motor unit can vary; smaller motor units control a few muscle fibers and are typically involved in fine motor skills, while larger motor units control many fibers, suitable for more powerful movements. Understanding motor units is crucial for personal trainers as it helps them grasp how different types of exercise influence muscle contractions and overall strength development.