Which muscle is involved in the flexion of the elbow joint?

The biceps brachii muscle is primarily responsible for the flexion of the elbow joint. This muscle is located in the upper arm and consists of two heads that originate from different points on the scapula. When the biceps contracts, it pulls the forearm up toward the shoulder, resulting in elbow flexion. This action is crucial for many everyday movements, such as lifting and pulling.

Additionally, the biceps are often engaged during activities that require bending the arm, such as carrying objects or performing weightlifting exercises. The role of the biceps in elbow flexion is well-documented and easily observable during physical activity, making it the correct answer for this question.