Final answer:
The statement is true; larger motor units activate more muscle fibers, resulting in stronger muscle movements, while smaller motor units control fewer fibers and allow for fine, detailed movements. This is due to motor unit recruitment which dictates muscle control and contractile strength.
Step-by-step explanation:
The statement is true: the larger the motor unit, the stronger the movement it produces. A motor unit consists of a motor neuron and all the muscle fibers it innervates. Large motor units activate a greater number of muscle fibers, which typically participate in gross movements like powerfully extending the knee joint. This leads to a stronger contraction force because more cross-bridges form between actin and myosin within the muscle fibers.
Conversely, smaller motor units, which have a lower threshold and higher excitability, control fewer muscle fibers and are thus responsible for fine, detailed movements such as eye movements or finger manipulations. The recruitment of motor units follows the principle that as more force is needed, larger units are gradually activated to increase the muscle contraction, known as recruitment.
The precision of muscle control corresponds with the size of the motor unit and the presence of more motor units allows for finer control. In summary, the size of motor units plays a crucial role in determining the type and strength of muscle movement.