Answer:
Triceps brachii.
Explanation:
Biceps brachii muscle is present in the upper arm that lies between the elbow and shoulder. This muscle help in the flexion of forearm.
The biceps brachii muscle can acts as the prime mover, this time the triceps brachii muscle assist as the synergist muscle. This muscle increases the function of the bicep brachii muscle.
Thus, the answer is tricep brachii muscle.
