The Purpose of Exercise

Updated: Nov 10, 2020

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One of the biggest industries in the United States economy, the fitness world is growing every day. One of their main messages, and sometimes their only line, is that the purpose of working out is to lose weight. They have jacked men and women with thigh gaps showing off this supplement or that workout equipment while bragging about how many inches they have dropped off their waist.

So the general population drags themselves to the gym - just to sign up! Then never make it regularly. Because they believe they have to spend three hours at the gym and buy a fancy protein shake to be in shape. Everyone gives up so quickly!

Do you want to know a secret? Most people who exercise regularly don’t do it to lose weight. And those models showing off those weight loss programs? They haven’t ever had a weight problem. It’s all a bunch of BS.

Physical exercise has many other health benefits, both physical and mental. Physically, working out increases heart rate and lung capacity; it strengthens muscles and bones while allowing the brain, digestive system, and endocrine system to be more efficient. Mentally, exercise can increase alertness and focus; it can increase confidence and mood. Let’s break that down.

Heart/Circulatory System

Cardiac output (how much blood is being squirted out of the heart in one heartbeat) increases during physical exercise because oxygen delivery is the predominant factor in determining exercise tolerance. The body increases blood output by increasing the force of the blood pump and by increasing the heart rate.

During exercise, particular peripheral blood vessels constrict, diverting blood from inactive tissues to the muscles. The skeletal muscles can take up to 88% of the cardiac output during exercise, whereas at rest, it is allowed 21%. As the body moves, the blood spreads more rapidly throughout the body. This increase in circulation helps with temperature control and enhances overall body function.

Consistent, long-term exercise increases the strength of the cardiac muscle and allows it to more efficiently supply the body with oxygen. When a person says they want to get back in shape, they mean they want their heart muscle to be strong enough to pump the needed oxygen for the duration of their desired activity.

Being fit is a sliding scale. There isn’t a set point of being “in shape” or out of shape. One person can be fit by walking two miles in forty-five minutes while another person can be considered fit by running three miles in thirty minutes. A non-athlete can increase their cardiac output four-fold during exercise, 5 L/min to 20 L/m, whereas an athlete can increase their cardiac output six to eightfold, 5 L/m to 40 L/m. Someone who is in shape can be anywhere in between.

Overall, physical exercise can decrease the risk of cardiovascular diseases. By reducing health risks, an individual can live longer and spend less on medical bills.


During exercise, the lungs increase their rate and depth of breathing. The amount of oxygen and carbon dioxide in the lungs does not change significantly with training. Sensors inside the body give feedback to the brain’s respiratory center, so it knows how hard to breathe in response to physical activity.

The lungs can change from regular, long term exercise. The muscles that operate the lungs strengthen and allow the chest to expand further. The lungs become more efficient with training in that they can consume oxygen better (increase in VO2 max). Activity increases the number of capillaries in the lungs so they can exchange more oxygen molecules.


The short-term effect of exercise on muscles is the consumption of calories. Aerobic (with oxygen) training, such as walking, allows the muscles to get enough oxygen throughout the workout and prevents muscle fatigue. The body consumes oxygen and burns energy during this type of exercise.

Anaerobic (without oxygen) exercise such as sprinting creates an oxygen deficiency in the muscle and leads to muscle fatigue. When the muscle doesn’t have enough oxygen, it turns to an alternative source, phosphocreatine. When the muscle takes energy from phosphocreatine, it leaves lactic acid. The buildup of lactic acid causes fatigue and makes your muscles sore. After you stop exercising, the muscle must get rid of the lactic acid buildup and replenish its oxygen supply, so it continues to work and consume oxygen for a time after the workout, burning more calories.

The long term effects of exercise are an increase in muscle mass, aka hypertrophy. The muscle begins to take shape. The bigger a muscle, the more oxygen it consumes, and the more calories it burns at rest.


High impact exercises cause the bones to build itself up to accommodate the stress. The osteocytes (a type of cell in the bone) act as mechanosensors (sensors that respond to movement) and translate mechanical stimulus into a signal to build bone tissue. The bone becomes denser, which reduces the risk of osteoporosis and other bone diseases.


The three main hormones involved in exercise are cortisol, epinephrine/norepinephrine, and growth hormone. All hormones promote the breakdown of fat into glucose for energy. Epinephrine/norepinephrine and cortisol, along with glucagon, mobilize glycogen (strings of glucose) from the liver to increase glucose levels in the blood. These hormones increase the body’s metabolism.

Exercise has a positive effect on your mental state. The increases in epinephrine/norepinephrine increase the sense of euphoria, which decreases stress and anxiety. It also increases alertness and energizes the individual. Exercise can reduce levels of the stress hormones, adrenaline and cortisol, in the body, which also decreases stress and anxiety.

Research has shown an inverse relationship between exercise and depression. People who exercise regularly are less likely to have depression. The exact cause and effect haven’t been nailed down yet.

Digestive System

Exercise can relieve digestive issues such as irritable bowel syndrome and constipation. Moving can increase digestion because the food is pushed through the intestines more efficiently. The body also needs more fuel, so the system converts carbohydrates, fats, and proteins into fuel more effectively.

Exercise is more than just burning calories; it has so many long term health benefits. Now that you are inspired to start exercising, I also want to encourage you to do something you enjoy. Don’t spend three hours at the gym trying to figure out the equipment if you don’t adore it! Take a dance class or find a walking trail. There are so many ways to exercise that don’t require being bored.

Textbook Sources:

Silverthorn, Dee Unglaub, et al. Human Physiology: an Integrated Approach. Pearson, 2016.

Further Reading:

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