the muscle is getting bigger because its pushing on the muscle behind it
to make it tight
You can flex skeletal muscles voluntary. These are the muscles you can control and move consciously. Smooth muscles and cardiac muscles, which work involuntarily, cannot be consciously flexed.
Your hamstring muscles.
Hamstring
The sternocleidomastoid muscles are the ones that flex when the intercostals are flexed. This will also cause the scalene muscles to flex.
To flex your chest, you tighten the muscles that are in that area. This might include your arms or back as well, but you tighten the muscles in your chest and abs.
Muscles can contract and shorten
i done no
You flex your muscles to do this and these pull on the tendons which link the muscles to the bones.
brechioradialis
Biceps Brachii flexes the forearm and the Triceps Brachii extends the forearm.
Function: flexion and radial deviation of the wrist, along with other muscles which flex the wrist and radially deviate the wrist, weak pronation of the forearm along with other muscles which pronate the forearm and weak flexion of the elbow along with other muscles which flex the elbow