How do motor unit recruitment patterns differ between volitional and NMES contractions?

How do motor unit recruitment patterns differ between volitional and NMES contractions?

• A. Volitional: asynchronous; NMES: synchronous
• B. Volitional: synchronous; NMES: asynchronous
• C. Both asynchronous
• D. Both synchronous

Answer: (A)

The key idea is how motor units are activated in time during different types of contraction. In voluntary contractions, motor units are recruited in an asynchronous, order-based way: small, fatigue-resistant units fire first and their activity is spread out over time, with larger units stepping in as needed. This asynchronous pattern produces smooth, graded force and helps delay fatigue. With NMES, the electrical stimulus hits many nearby motor neurons at once, so a broad group of motor units is activated nearly simultaneously. That leads to a more synchronous contraction, with a rapid, forceful response that is less finely graded and can fatigue more quickly. So the correct concept is that volitional contractions are asynchronous, while NMES contractions are synchronous.

The key idea is how motor units are activated in time during different types of contraction. In voluntary contractions, motor units are recruited in an asynchronous, order-based way: small, fatigue-resistant units fire first and their activity is spread out over time, with larger units stepping in as needed. This asynchronous pattern produces smooth, graded force and helps delay fatigue.

With NMES, the electrical stimulus hits many nearby motor neurons at once, so a broad group of motor units is activated nearly simultaneously. That leads to a more synchronous contraction, with a rapid, forceful response that is less finely graded and can fatigue more quickly.

So the correct concept is that volitional contractions are asynchronous, while NMES contractions are synchronous.