These chemicals are released by your pituitary gland, which is located in the base of your brain. Endorphins make you feel exhilarated and happy and block any feelings of pain, so you can power through any discomfort caused by exercising. That's why people become addicted to strenuous forms of exercises and experience "runner's high."
Estrogen determines whether carbs or fat fuel the body during an intense exercise session. Women tend to burn fat for fuel, while men tend to burn carbs, because women have higher estrogen levels. When women undergo menopause, they usually experience some weight gain because of lowered estrogen levels.
See more chemicals released while exercising.
Dopamine is a pleasure chemical. Studies have found that a brain with a dopamine receptor deficiency is more prone to weight gain, because eating quickly easily raises dopamine levels. Those with fewer receptors need more dopamine in the bloodstream (aka more food) to reach the same level of satisfaction as someone with a normal amount. This is even more reason to work out regularly to keep those dopamine levels up in order to keep overeating and weight gain at bay.
Growth factors are the hormone-like compounds that work with satellite cells to help stimulate and regulate production of more muscle. Growth factors like hepatocyte, fibroblast, and insulin send signals to the satellite cells to move to the damaged muscle area, repair the damage following exercise, and regulate muscle mass growth, respectively.
A chemical responsible for happiness, restful sleep, and a healthy appetite, serotonin levels will increase if you work out regularly. Serotonin works with endorphins to make working out a pleasurable activity. In addition, more serotonin means more energy and clearer thinking.