When you bend your arm, your biceps muscle contracts while your triceps muscle relaxes. These two muscles work in opposition to each other to allow for movement at the elbow joint.
Here's a more detailed explanation:
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Biceps Contraction: The biceps brachii, located on the front of your upper arm, contracts (shortens and thickens). This contraction pulls on the forearm bones (radius and ulna) towards the shoulder, causing the arm to bend at the elbow.
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Triceps Relaxation: The triceps brachii, located on the back of your upper arm, relaxes. This relaxation allows the biceps to effectively pull the forearm upwards without resistance. If the triceps were to contract at the same time as the biceps, the arm would not bend.
In essence, bending your arm is a coordinated action between two opposing muscle groups: the biceps (flexor) and the triceps (extensor). This principle of antagonistic muscle pairs applies to many movements throughout the body. The nervous system precisely controls the contraction and relaxation of these muscles to produce smooth and controlled movements.
