What muscle group is primarily responsible for flexing the arm at the elbow joint?

The biceps brachii, commonly referred to as the biceps, is primarily responsible for flexing the arm at the elbow joint. This muscle is located on the anterior part of the upper arm, and it has two heads that originate from the shoulder, allowing it to perform two main functions: flexion of the elbow joint and supination of the forearm (turning the palm upwards).

When the biceps contracts, it pulls on the radius bone in the forearm, effectively bending the arm at the elbow. This is why exercises that work the biceps, such as bicep curls, are particularly effective for strengthening the flexion motion at the elbow.

The other muscle groups mentioned play different roles; for example, the triceps are responsible for extending the arm, the deltoids are primarily shoulder muscles involved in arm abduction and flexion at the shoulder, and the pectorals are involved in movements that bring the arms across the body and push actions. Thus, they do not primarily contribute to elbow flexion like the biceps do.