Which muscles are the first recruited in forearm supination and pronation?

What will be an ideal response?

ANS:
The single-joint supinator and pronator are the supinator muscle and the pronator quadratus. One might assume, therefore, that these muscles are the most consistently active during active supination and pronation, respectively. The two-joint supinator is the biceps brachii, and the two-joint pronator is the pronator teres. These are likely to be active when additional force is necessary, or simultaneous elbow flexion is desired.