when you bend your arm
A flexor is a muscle that causes a joint to bend. In contrast, an extension is a muscle that straightens a joint.
it contracts
When you bend your arm at the elbow and feel your biceps your upper arm muscle contracts.👏👏
The muscle/muscles that bend your arms are called Flexor and Extensor.
They are the opposite muscle to the biceps. If you bend your arm to make the muscle on the top (the biceps) bulge, the muscle on the bottom (the triceps) relaxes. The triceps is on the back of your arm, and is used to straighten the elbow.
Believe it or not, the bicep muscle has almost nothing to do with arm strength. That muscle is mostly responsible for allowing you to bend your arm or flex it towards your shoulder.
When a bicep contracts it pulls on tendons causing the arm to bend at the elbow.
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The biceps is the muscle on the front of the upper arm; it bulges when you bend your arm at the elbow. The triceps is the muscle on the back of the upper arm. Note that "biceps" and "triceps" can be either singular or plural. It is incorrect to say "bicep" or "tricep."
Skeletal muscles work in pairs, with one muscle contracting (agonist) to bend the arm at the elbow and the other muscle relaxing (antagonist). When bending the arm, the biceps brachii contracts and the triceps brachii relaxes. When straightening the arm, the triceps brachii contracts and the biceps brachii relaxes. This coordinated action allows for smooth and controlled movement at the elbow joint.
Inn other words muscle flexing can be called muscle shortening and extension when muscle is elongating. For example when you bend you arm towards your shoulder your bicep muscle is shortening and you can feel a bump. When you extend your arm you can feel that the bump is stretching out and disappearing, that is muscle extension.