What Happens To Your Body If You Don’t Exercise

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Infographic - What Happens to Your Body From Exercise

The last decade or two has witnessed an epidemic of obesity and chronic illness sweeping the developed nations of our world.  Much of this can be traced to the increasingly sedentary habits of affluent adults and children who sit in front of their TVs, computers, or video game consoles for hours at end and see little need to get up or out of the house for any purpose beyond the absolute essentials.  What many people don’t realize is just how severely this kind of inactive lifestyle is slowly destroying their bodies and health.

Our bodies were designed to move.  Skeletal muscles, the ones that articulate our bones and allow us to move, make up 40% of a healthy person’s total weight.  Our skeleton, which supports our weight and allows us to stand upright, comprises another 15% or so.  This means over half of our body is designed to make us move, which until fairly recently in human evolution was necessary for survival.

Remember Newton’s First Law of Motion: a body in motion tends to stay in motion and a body at rest tends to stay at rest.  This applies just as surely at the micro level with individuals as it does at the macro level with celestial bodies.  Let’s examine more closely exactly what happens to a human body in motion—and one at rest.

When we exercise, our muscles contract or shorten, which moves our bones and propels our body in motion.  If the load or force applied to the muscles and bones is greater than that which we’re normally accustomed to, our body quickly sends nutrients to the locations of stress (protein to our muscles and calcium to our bones) to build the strength and mass needed to support these new loads.  Tiny tears occur in the muscles, which are repaired and reinforced with extra tissue in much the same way bones grow back stronger when cracked or broken.  These larger and denser muscles become thicker in the middle portions where the primary contractions occur, which in time produces the targeted ‘curves and valleys’ on our body that most people find aesthetically attractive.

Because our muscles work harder when we exercise, they have a higher demand for oxygen.  Oxygen is the fuel that enables our body to convert glucose into ATP, which powers the energy process at the cellular level. Our autonomic nervous system causes our lungs to expand and contract more deeply and frequently, delivering oxygen to our circulating bloodstream and increasing our red blood cell count, which carries the oxygen to the tissues needing the extra energy.  The dense new tissue created from exercise includes new blood transporting capillaries, which improves our skin tone and color.

In order to transport the greater quantity of oxygen needed to fuel our muscles during exercise, our heart begins to beat faster to pump the expanded volume of red bloods cells more quickly throughout our bodies.  Because the heart is a striated muscle much like our skeletal muscles, this increase in load and contraction of the heart has a similar effect: it becomes stronger, larger, and more richly populated with healthy new blood vessels, which helps keep it unclogged and functional for a longer and more capable lifetime of activity.

The increased flow of oxygenated blood to the brain also triggers a number of beneficial hormonal and chemical reactions.  Endorphins are quickly released in larger quantity into the bloodstream, which masks our perception of pain and stress from exertion, acting as an analgesic similar to morphine.  Serotonin levels are boosted, which makes us feel happier and more content, also regulating our appetite and sleep/wake cycles, and stimulating our libido.  Exercise also sparks dopamine production, which creates an immediate and prolonged pleasure sensation, familiar to many runners who experience ‘runner’s high’.  Finally, larger quantities of the ‘love drug’ oxytocin is released during exercise, which is an important chemical for producing feelings of trust and intimacy between individuals, and which is also produced during orgasms and breastfeeding.

At a more visceral level, exercise increases the rate of cellular turnover and replacement almost everywhere within our body.  The rate of cellular turnover varies from a few days for tissues such as the lining of our stomach to a few years for our liver and fat tissue.  Various waste products and toxins build up in our cells, which are implicated in the development of certain chronic and fatal diseases such as cancer and fibromyalgia.  The quicker we can remove old cells and replace them with healthy new cells, the less hard our immune system has to work and the less likely it will lose the ability to distinguish unhealthy vs. healthy tissue.

On the outside of our body, those fat cells that take so many years to turn over naturally are quickly consumed by the caloric deficit you create when you exercise, as triglycerides within the fat cells are metabolized for energy after the first ten to fifteen minutes of sustained activity.  These fat stores are consumed indiscriminately from all areas of your body as you whittle down the loose gelatinous tissue, revealing your newly toned muscles and making you look like a finely carved sculpture.

Finally, the increased energy expenditure associated with exercise generates internal heat, which is regulated through the skin in the form of sweat. Regular healthy sweating not only helps to cleanse and unclog your pores, but also helps to expel various toxins including heavy metals and kills disease- and infection-producing viruses and bacteria that cannot survive in environments beyond your regular body temperature.  Yet another route for the elimination of built-up toxins is through the quenching of the exercise-induced thirst mechanism via the increased consumption of water and through the stimulation of our digestive and bowel elimination processes.

Let’s summarize these internal biochemical reactions that exercise stimulates, and their beneficial effects:

+ Increased load-bearing activity on the musculoskeletal system stimulates the production of stronger and denser muscles and bones, making you more shapely, functionally fit, and less prone to injury;

+ Increased oxygen delivery stimulates the production of hemoglobin-rich red blood cells and capillaries, improving skin tone and color;

+ Numerous mood-enhancing hormones and neurotransmitters are released including endorphins, dopamine, serotonin, and oxytocin, which combine to improve appetite, sleep/ wake cycles, libido, and general feelings of happiness and social connectivity;

+ New healthy tissue formation in various internal and external organs promotes the increased turnover of cells and the speedier removal of waste- and toxin-accumulating old cells and the more effective functioning of the immune system;

+ Fat is slowly burned off as it is used to fuel the increased energy requirements of new physical activity, removing the smooth and loose overlay of adipose tissue, revealing the newly formed and more firm and shapely underlying muscle tissue;

+ Increased sweating from exercise keeps pores unclogged and expels heavy metal toxins and disease-producing viruses and bacteria;

+ Increased water consumption helps remove toxins via flushing through the kidneys and solid wastes via stimulation of the digestion and bowel elimination functions.

On the other hand, the exact opposite functions and effects are induced from prolonged periods of inactivity:

– Muscle tissue withers and weakens as high-energy-consuming and now superfluous tissue is carted away by the same proteolytic systems that delivered the excess protein deposits during muscle formation.  Excessive loss of muscle is associated with poor prognosis in several diseases including diabetes, cancer, sepsis, and heart failure;

– Similar mechanisms are involved in progressive bone demineralization from lack of weight- bearing physical activity, leading or contributing to osteoporosis, osteoarthritis, broken hips, joint replacements, and the formation and painful passage of kidney stones;

– Slower and less vigorous oxygen uptake reduces red blood count and hemoglobin levels, which can lead to anemia and is implicated in the development of leukemia and blood clots causing strokes and heart attacks.  Poor blood flow is also the primary cause of erectile dysfunction (ED);

– Low levels of exercise-induced serotonin contributes to various anxiety disorders including OCD, depression, and elevated suicide rates;

– Depleted levels of exercise-induced dopamine can exacerbate the suffering of various chronic pain and autoimmune disorders such as fibromyalgia, MS, and others;

– Low levels of oxytocin can lead to anti-social behavior, couple/ child abandonment, and loss of libido and sexual enjoyment;

– Blocked or diminished turnover of new tissue and cell formation can lead to the buildup of toxins, organ inflammation, and the development of autoimmune disorders;

– High body fat percentage and obesity is heavily implicated in the development of diabetes, which can subsequently lead to heart and kidney disease, stroke, vision loss, and amputations;

– Irregular or insufficient sweat expression can cause clogged pores, blackheads, acne, the build-up of heavy metal toxicity, and the increased transmission and adoption of touch- based diseases such as MRSA, flu, and colds.

These are the immutable dynamics embedded within everybody’s DNA. In light of these facts, you have a choice.  You can sit on your butt all day long, enjoying the comforts and conveniences of our twenty-first century sedentary lifestyle, oblivious to how the cells in your body are slowly calcifying and preparing for an early and likely painful exit.  Or you can get up and outside of your home or office at least once a day for a few minutes and do something good for your body, to keep it finely tuned and capable of providing you a long and vibrant future.  As in all things in life, small sacrifices in the present pay generous dividends in the future: use the life-affirming gifts you’ve been given, or quickly lose them!

By Reid Jenner


  1. Andy

    Hi Mr. Jenner,
    Excellent article, and really interesting concepts. I’ve been using a FitBit Charge HR and program to increase my fitness and I’m doing well. One question though. How long does it take, if you lost most of your muscle due to inactivity due to major trauma and the resulting surgeries with 3 units of blood loss and left un-replaced (only fluids given, no blood given due to high rate of AIDS virus in blood products), before you can begin to regain back the lost muscle that you once had?
    I just want to know what I am up against. Regaining muscle is slow and difficult.
    Thank you for your time,

    1. Andy,

      Thanks for your comments and feedback — glad you found my article on the effects of exercise helpful. The good news is that recovering lost muscle is usually easier and faster than building brand new muscle tone and mass. Your body has a ‘muscle memory’, and depending on how long it’s been since you lost your muscle strength and mass, it should only be a matter of weeks before you regain what you last had. If you’re working out properly (pushing to and slightly beyond your current max limits) and regularly (i.e. at least 3 times per week), normally within 6-12 weeks you should begin to see quite noticeable improvement. If you have other serious health issues, including major loss of blood volume, this can slow the recovery process a little bit further. Your body has an amazing adaptive and recovery ability, and was designed to work and move, so the best thing you can do to recover your full health is to exercise regularly and vigorously. Good luck, and let me know how it goes! 🙂

      1. Andy

        Thank you for your encouragement. It’s not often to get such a well thought out reply. I know I am ‘up against’ a lot of change. Exercise, I do it, but it is hard on some days. Probably the worst problem of the blood loss is the less oxygen your blood can carry to the body. I want to share your article with a few friends and family, but there is no share button to email your article to others who I know could benefit from reading.

  2. I’ve restarted a diet every Monday for 35 or so years and am now over 30 pounds overweight. Your article is very motivating to stay active!

  3. Hi Kim,

    Thanks for sharing your experience. You may also find this other article on my blog helpful in providing guidance and motivation to meet your weight management goals: Three Steps to Effective Weight Control. You can find it by clicking on the month of May in the Archives listing in the sidebar to the right of this article.

    Let me know how it goes and if I can help any further!


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