The Strain
There is three types of muscle, cardiac, smooth, and skeletal muscle. Muscles can either be controlled, or they just happen, you don't have to think about it. This is called voluntary muscle or involuntary muscles. Some muscles can be controlled for some time, but after awhile your body kicks in and makes you urinate, defecate, breathe, blink or whatever else you are trying to control.
Skeletal muscle is the muscle that lets bones move, smooth muscle is the muscles in charge of moving food throughout the digestion system. It also lines the blood vessels, it pushes the blood to and from. Cardiac muscle is the heart. Your heart is a very strong muscle that needs a lot of energy to work.
There are another two classifications of skeletal muscle, flexors, and extensors. When you straighten a body part, you are using an extensor, when you bend a part of your body you are using a flexor.
Tendons connect muscle to bones. They are important because they connect the skeletal muscle to the bone so you can move. Your muscular system is meant to move, and be able to be flexible.
If you don't use a muscle, the muscle shrinks because it has no use. This is why when you break your arm, and it gets put in a cast that your arm is smaller than your other uninjured arm. When you are in physical therapy, after an injury, you are there to gain flexibility and strength back.
Things that can go wrong. A strain, a strain is an overstretched or torn muscle or ligament. If you exercise too much, your tendons don't have the time to heal again. So they flame up, your body can't heal injuries that fast, so the tendons swell up. This is called tendonitis, tendonitis takes a very long time to heal, a lot of rest is needed.
People can use anabolic steroids they heal the muscles by making them stronger. Steroids damage many vital organs like the heart, liver. and kidneys. They can cause high blood pressure. They can even stop the growth of bones. Not to mention they are illegal to use in any sports.