the muscle is getting bigger because its pushing on the muscle behind it
to make it tight
Your hamstring muscles.
hamstring group of 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.
The quadriceps extends the thigh and the hamstring muscles flex the knee
Voluntary muscles can be flexed.
brechioradialis