After a tough day at work, you may feel anxious and stressed. Hitting the gym can help relieve some of these feelings, but to understand why exercise makes you feel more relaxed after a hectic day, you have to understand the relationship between adrenaline and stress.

Adrenaline is released from the adrenal glands when the body believes it is involved in a stressful situation. In fact, we're designed so that our bodies will even build up adrenaline levels in anticipation of danger. This adrenaline rush prepares the body for what we call "fight or flight." With a rush of adrenaline, your heart rate and breathing rate increases and your senses become more acute, readying the body for flight. Nutrients are released to sustain muscular activity and blood flow is regulated away from less important organs to the muscles to prepare for a fight. The body keeps up this preparation until it no longer feels threatened.

This reaction helps us survive by running away from an attacking lion or fighting off a suitor interested in our mate. In modern times, we don't have to worry about fighting off hungry predators, but we still receive that rush of adrenaline when we're having a bad day at work, fighting with a loved one or even battling our way through traffic. Most of the items that bring stress into our lives are hard, if not impossible, to escape. In this continually stressful environment, our bodies are often in an active state of fight or flight. This has a negative effect on the body, because its focus is shifted away from our immune and digestive systems, producing a weakened immune system and digestive problems, not to mention overworking the heart.

Adrenaline increases dramatically when the body senses a threat, but it decreases quickly after the threat has dissipated. The increase in adrenaline is often called the adrenaline rush, which is what those adrenaline junkies who bungee jump off bridges or skydive are searching for. This initial rush of adrenaline makes you feel empowered, like you can conquer the world. The decrease in adrenaline afterwards is known as the adrenaline crash, and this can make you feel anxious or even negative. Those who suffer from depression have been found to experience an extremely drastic drop in adrenaline.

You can use this adrenaline rush to add a boost to your exercise and release your stress. This is something that many bodybuilders do to take their workouts to the next level. Use the pent up adrenaline by converting it into the power and energy you need to push through your workout. Exercising also helps to release endorphins which give you a natural high, helping to relieve the stress you're feeling and allowing your body to relax and break the fight or flight cycle it's been stuck in, if you've had an overly stressful day.