One reason exercise is so good at relieving stress is because it reduces cortisol levels. Cortisol is a hormone released from the adrenal gland in times of stress, such as when you feel anxiety, anger or fear. Chronically elevated cortisol levels ultimately inflame and can even damage organs.
Exercise burns cortisol, and thereby makes us healthier and happier, Debbie Mandel, author of “Turn On Your Inner Light: Fitness for Body, Mind and Soul” (Busy Bee Group, 2003), told LiveScience. Exercise also stimulates the brain’s pituitary gland to release endorphins, which are neurotransmitters that have naturally feel-good effects.
The CDC recommends doing muscle-strengthening activities that work all the major muscle groups (legs, hips, back, abdomen, chest, shoulders and arms) two or more days a week, as well as at least 2 hours and 30 minutes of moderate-intensity aerobic activity, such as speed-walking, every week.
That may seem like a lot, but just going out for a brisk, 10-minute walk three times a day for five days a week will add up to 150 minutes of moderate-intensity activity. [7 Common Exercise Errors — And How to Fix Them]