Stress ! Yes, we are all stressed, it is a natural feeling aimed at protecting us from danger and prepare us for fight og flight. Research has shown exercise to be a stress reliever.
There are many reasons to explain why. One includes the fact that exercise increases the hormone epinephrine, another name for adrenaline. This hormone is responsible for an increase in blood flow, which carries more oxygen to the brain, thus making you more alert. Being more alert and aware of your surroundings helps you to deal with stress effectively. Also, exercise stimulates the release of other hormones called endorphins, or the “feel good hormones.” These help to improve mood and feelings.
Many people find that they feel better after a stressful day if they exercise. A good friend of mine Dr. Ólafur Ævarsson a psychiatrist has runs a good blog on stress related issues.