What is the primary function of flexor muscles?

Flexor muscles primarily function to reduce the angle at the joint, a movement known as flexion. When flexor muscles contract, they pull the bones of a joint closer together, resulting in a decrease in the angle between them. For example, when you bend your elbow, the biceps brachii muscle (a flexor) contracts, causing the forearm to move closer to the upper arm, thereby reducing the angle at the elbow joint.

This action contrasts with the role of extensor muscles, which work to increase the angle at a joint by straightening it. While stabilizing the joint and moving limbs towards or away from the body's midline are also important functions of various muscle groups, these actions are not the primary role of flexor muscles. The focus here is specifically on the action of flexion, which is fundamental to activities such as writing, lifting, and running.