During exercise, some physical changes are obvious – you feel your heart pound, you breathe more rapidly and you feel your muscles burn and become fatigued. But there are other chemical changes of which you may be less aware.
During all exercise, your body uses the muscles to generate motion. As the muscles work, they rely on other systems in the body to help them keep going. For example, your heart rate increases so that more blood is pumped to the muscles to keep them working. Your digestive system slows down so that it’s energy can be redirected to the muscles to use.
The chemical your body uses during exercise as its energy source is called adenosine triphosphate or ATP.
According to Craig Freudenrich, M.D., in order for your body to produce this chemical, it needs three things: oxygen, because it is consumed to produce ATP; elimination of metabolic wastes, such as carbon dioxide and lactic acid that are generated by the body’s chemical reactions; and removal of heat that is generated by the working muscle.
Working muscles extract oxygen from the blood three times faster than resting muscles. This means the body has to increase oxygen-rich blood flow to your muscles when you exercise. By increasing the rate of your breathing, your lungs expand further, increasing ventilation, which allows more oxygen to enter the blood stream. When your heart rate increases, the amount of blood pumped by the heart increases, as does the force and speed it pumps. At a maximum heart rate, the heart is pumping about 20 to 25 liters per minute, according to Dr. Freudenrich. Lastly, by diverting the blood from nonessential organs, such as the stomach and kidneys, more blood can flow to the muscles. This can create almost five times the blood flow to your working muscles.
All of the extra blood flowing in the body is performing two important functions – carrying much needed oxygen to the muscle and transporting the metabolic waste away. Once the blood has reached your muscles, it extracts the oxygen and leaves behind carbon dioxide, which is a waste product that needs to be eliminated. Hemoglobin, which is found in red blood cells, carries most of the oxygen in the blood to the muscle. However, it also binds to the carbon dioxide in the blood and carries it back to the heart and lungs, and the cycle repeats.
Lactic acid is caused when your body makes ATP anaerobically (meaning without oxygen). When you perform strenuous exercise, your body needs energy faster than it can produce using aerobic methods. It does this by breaking down its store of glycogen that is held in your muscles. Your cells turn glycogen into glucose, which is used to make ATP. The byproduct of this is lactic acid, which is what causes the muscle burn you feel when you exercise. To prevent this lactic acid from building up, stay well-hydrated before, during and after you exercise, and be sure to incorporate a cool-down period into each workout.
Most people feel warm or hot when they exercise. This is caused by the chemical energy that’s created by the working muscles. Some of this energy cannot be used by the body and is eliminated as heat. This heat causes the blood vessels in the skin to expand, which increases blood flow to the skin and allows the excess heat to escape the body into the air. During exercise, your skin may become flushed, you may feel hot and you will sweat. This is how the body cools itself. It’s important to remember that sweating is a loss of fluid from the body, so it’s important to continually hydrate during exercise to prevent dehydration.
The body’s systems work together to meet the needs of actively engaged muscles. Consistency in your workouts improves the way these systems work together, thereby improving your performance. Understanding your body’s chemical reactions will help you enhance your workouts and help you lead a healthful lifestyle.