The arm muscle that both flexes and supinates the forearm is the
a. Brachialis
b. Brachioradialis
c. Biceps brachii
d. Triceps brachii

Verified step by step guidance

1. Step 1: Understand the actions of the muscles listed. Flexion of the forearm means bending the elbow, decreasing the angle between the forearm and the upper arm. Supination of the forearm means rotating the forearm so the palm faces upward or forward.
2. Step 2: Review the primary function of the brachialis muscle. The brachialis is mainly responsible for flexing the forearm at the elbow but does not contribute to supination.
3. Step 3: Consider the brachioradialis muscle. It assists in flexion of the forearm, especially when the forearm is in a mid-pronated position, but it does not supinate the forearm.
4. Step 4: Examine the biceps brachii muscle. This muscle is well-known for both flexing the forearm at the elbow and supinating the forearm, making it unique in performing both actions.
5. Step 5: Recognize that the triceps brachii is primarily responsible for extending the forearm at the elbow and does not flex or supinate the forearm.

Key Concepts

Muscle Actions: Flexion and Supination

Flexion refers to decreasing the angle between two body parts, such as bending the elbow. Supination is the rotational movement that turns the palm upward or forward. Understanding these actions helps identify which muscles perform these specific movements at the forearm.

Anatomy of Forearm Muscles

The forearm muscles include the brachialis, brachioradialis, biceps brachii, and triceps brachii, each with distinct functions. Knowing their origins, insertions, and primary actions is essential to determine which muscle flexes and supinates the forearm.

Function of the Biceps Brachii

The biceps brachii is a two-headed muscle that primarily flexes the elbow and supinates the forearm. It is unique among the listed muscles for performing both actions simultaneously, making it the correct answer to the question.