The muscle pushes against the other muscle that does the opposite action. Take the bicep for example the bicep pulls while the tricep also pulls. the two muscles cancel each other out, but while still pulling making the muscle more showing.
When you flex a muscle, it puts pressure on the muscle fibers, causing microscopic damage. This damage triggers an inflammatory response, leading to pain and soreness in the muscle.
When you flex your bicep, the muscle contracts and pulls on the tendons that attach it to your bones. If there is inflammation or strain in the muscle or tendon, it can cause pain when you flex your bicep.
supraspinatus muscle
The triceps brachii muscle does not flex the elbow; it is responsible for extending the elbow joint when it contracts.
Flex Your Love Muscle - 2012 was released on: USA: 8 January 2012
All Muscle with Funkmaster Flex - 2006 was released on: USA: 2006
If you are asking what does someone mean when they say "I have muscle," it is slang for having a muscle "stick out" when you flex it.
The flex
hamstrings
The Quadriceps.
Bicep.
the muscle is getting bigger because its pushing on the muscle behind it