biceps, triceps, supinators and pronators
Explanation:
The four main muscles of the arm — the portion of the upper limb that runs from the shoulder to the elbow — fall into two large groups: an anterior and a posterior.
The anterior is formed by the brachial, coracobrachial, and biceps brachii muscles, which promote flexion of the forearm over the arm.
The posterior group is composed of a single, very large muscle, the triceps brachii, responsible for the extension of the arm and forearm. The names biceps and triceps derive from the presence of two and three fleshy masses (muscle bellies), respectively, in each of these muscles.
The forearm muscles - which are quite numerous - can be divided into three groups: anterior, lateral and posterior. The main muscles of the anterior region are the brachioradialis and the round pronator, which also participate in the forearm flexion over the arm.
The lateral and posterior muscles of the forearm perform more or less the same functions, that is, they promote the extension of the hand, the rotation of its palm downwards (square pronator) or upwards (long supinator and short supinator). These last two movements are technically called supination and pronation.
