The bicep bends the arm by contracting and pulling on the radius bone in the forearm, effectively bringing the forearm closer to the upper arm.
Here's a breakdown of the process:
- Muscle Contraction: The bicep brachii muscle, located on the front of the upper arm, contracts. This contraction is triggered by nerve impulses.
- Tendon Connection: The bicep has tendons that attach it to bones. At the shoulder, it has two attachments, hence the "bi" in bicep. The relevant attachment for bending the arm is the one connecting to the radius bone in the forearm, near the elbow.
- Leverage System: The contraction pulls on this tendon, which in turn pulls on the radius bone.
- Forearm Movement: Because the tendon is attached near the elbow joint, pulling on the radius causes the forearm to rotate around the elbow joint, bending the arm. The bicep works in opposition to the tricep muscle, which extends (straightens) the arm.
- Supination Assistance: As a secondary action, the bicep also contributes to supination, which is the rotation of the forearm so that the palm faces forward or upward. This is because of the specific point of attachment to the radius.
In short, the bicep shortens upon contraction, pulling on the radius bone via its tendon, which then causes the forearm to flex (bend) at the elbow joint.
