In volitional contraction, large motor units are recruited as what occurs?

In volitional contraction, large motor units are recruited as what occurs?

• A. The contraction strength increases
• B. The muscle length increases
• C. The firing rate decreases
• D. The contraction slows

Answer: (A)

In volitional contraction, motor units are recruited following the size principle: small, low-threshold units fire first for lighter force, and as the demand for force increases, larger, high-threshold motor units are recruited to generate more power. This means large motor units come into action as contraction strength rises. The other factors listed—muscle length changes, firing rate decreasing, or the contraction slowing—do not drive the recruitment of large motor units in this voluntary pattern. As you need more force, the nervous system typically increases the overall drive, which often includes increasing the firing rate of active units in addition to recruiting more units.

In volitional contraction, motor units are recruited following the size principle: small, low-threshold units fire first for lighter force, and as the demand for force increases, larger, high-threshold motor units are recruited to generate more power. This means large motor units come into action as contraction strength rises. The other factors listed—muscle length changes, firing rate decreasing, or the contraction slowing—do not drive the recruitment of large motor units in this voluntary pattern. As you need more force, the nervous system typically increases the overall drive, which often includes increasing the firing rate of active units in addition to recruiting more units.