Which statement correctly describes the relationship between motor unit size and movement precision for complex movements?

• A. The number of fibers per motor unit does not affect precision
• B. Muscles involved in intricate movements have fewer fibers per motor unit.
• C. All muscles have the same number of fibers per motor unit
• D. Muscles for explosive movements have fewer fibers per motor unit

Answer: (B)

Complex movement precision relies on the ability to modulate force in very small, controlled steps. This comes from smaller motor units, where one motor neuron controls relatively few muscle fibers. When motor units are small, each additional activation can add a tiny amount of force, allowing the nervous system to finely gradate the overall contraction. Muscles responsible for intricate tasks—like those in the hands or eyes—toster to have these smaller motor units, providing the high degree of precision those movements require.

In contrast, larger motor units that innervate many fibers produce more force but with less grade control, which is why they’re associated with gross, powerful actions rather than delicate adjustments. The idea that precision is unaffected by motor unit size isn’t accurate, and saying all muscles have the same motor unit size isn’t true. Likewise, explosive movements typically rely on recruiting larger motor units to generate rapid, substantial force rather than fewer fibers per unit.