This is Your Body on… Exercise!
Posted by Katie
Whether you’re lacing up sneakers for a morning run, or snapping your helmet on for a bicycle ride, your body is responding to the conscious orders of your brain to move your muscles and as soon as those conscious movements begin, a series of rapid, automatic changes unconsciously occur throughout your body.
Your muscles immediately start to burn more energy to fuel their contractions. They do this by stepping up the conversion of oxygen and nutrients into adenosine triphosphate, or ATP (the fuel that all cells run on), inside each individual muscle cell. During sustained, aerobic activity, like a brisk walk or a steady swim, your working muscles burn carbohydrates and stored fat in about a 50-50 mix, using up to 15 to 25 times more energy than they do at rest. During an intense, short anaerobic effort, such as running a 100-yard dash or sprinting the length of the swimming pool, your muscles may require up to 120 times more energy than at rest!
Your heart immediately begins to beat faster in order to pump more blood to your muscles and other body tissues. During vigorous exercise, your heartbeat may rise to 150 beats per minute or more (compared with 70 or 80 heartbeats per minute at rest, for the average person). In fact, scientists have found that people’s heartbeats begin to beat faster even before they start to exercise, as the brain anticipates what’s about to happen. Whereas the average heart pumps about five liters of blood per minute at rest, the amount may increase to 20 liters per minute during vigorous exercise. The hearts of trained endurance athletes have been measured to pump as much as 40 liters in a minute!
Your blood vessels also go through rapid changes when you start exercising. Stimulated by nerve and chemical signals, the walls of the arteries leading to your working muscles relax, causing the arteries to widen. At the same time, peripheral veins constrict, forcing more blood into your central circulation. The result of all these changes is a vastly increased flow of blood to your exercising muscles carrying those all-important oxygen molecules and nutrients. Increased blood flow to the skin during light and moderate exercise encourages heat loss, which provides a cooling effect in addition to that provided by sweating. Meanwhile, blood flow is temporarily directed away from the kidneys, liver, digestive system and other organs not directly involved in exercise.
Your lungs also begin breathing faster and more deeply, supplying your body with more oxygen. This response results from a wide array of stimuli, including more output of carbon dioxide (the byproduct of using more oxygen), increased body temperature and rising acid production in the body. At rest, about 12 pints of air pass in and out of the average person’s lungs every minute. During vigorous exercise, this rate may increase to as much as 200 pints per minute.
Your metabolic rate can also increase between 4 and 20 times your resting metabolic rate, depending on how hard you exercise. This can carry over even after you’re done exercising because muscle burns more calories at rest than fat. The more muscle you build, the more calories you will burn in the long run.
You don’t have to be a professional athlete to benefit from exercise. So, try taking a brisk walk, lifting weights, joining a friendly game of Frisbee or just dancing around the house. The important thing is to burn calories. Find an activity you enjoy and you’ll be more likely to stick with it.