LOOK: This Is Your Body On Exercise

Updated: October 21, 2013

Whether you do it to lose weight, to reach a fitness goal or — dare we say it? — just for fun, exercise changes you.

There’s the red face and the sweating, the pounding heart and pumping lungs, the boost to your alertness and mood, the previously nonexistent urges to talk about nothing but splits and laps and PBs.

But while we all know that staying physically active is essential to a long, healthy, productive life, we don’t often understand exactly what’s happening behind the scenes.

We asked the experts to take us through — from head to toe — what happens in the body when we exercise. Neuroscientist Judy Cameron, Ph.D., professor of psychiatry at the University of Pittsburgh School of Medicine, Tommy Boone, Ph.D., a board certified exercise physiologist, and Edward Laskowski, M.D., co-director of the Mayo Clinic Sports Medicine Center spill the beans on what gets and keeps you moving. This is your body on exercise.

The body calls on glucose, sugar the body has stored away from the foods we eat in the form of glycogen, for the energy required to contract muscles and spur movement.

It also uses adenosine triphosphate, or ATP, but the body only has small stores of both glucose and ATP. After quickly using up these supplies, the body requires extra oxygen to create more ATP. More blood is pumped to the exercising muscles to deliver that additional O2. Without enough oxygen, lactic acid will form instead. Lactic acid is typically flushed from the body within 30 to 60 minutes after finishing up a workout.

Tiny tears form in the muscles that help them grow bigger and stronger as they heal. Soreness only means there are changes occurring in those muscles, says Boone, and typically lasts a couple of days.

Your body may need up to 15 times more oxygen when you exercise, so you start to breathe faster and heavier. Your breathing rate will increase until the muscles surrounding the lungs just can’t move any faster. This maximum capacity of oxygen use is called VO2 max. The higher the VO2 max, the more fit a person is.

Like any muscle, the diaphragm can grow tired with all that heavy breathing. Some argue that as the diaphragm fatigues, it can spasm, causing a dreaded side stitch. (Others argue a side stitch is due to spasms of the ligaments around the diaphragm instead, while others believe the spasms to originate in the nerves that run from the upper back to the abdomen and are caused by poor posture!) Deep breathing and stretching can alleviate the discomfort in the middle of a workout, and preemptive strengthening in the gym can ward off future issues.

When you exercise, heart rate increases to circulate more oxygen (via the blood) at a quicker pace. The more you exercise, the more efficient the heart becomes at this process, so you can work out harder and longer. Eventually, this lowers resting heart rate in fit people.

Exercise also stimulates the growth of new blood vessels, causing blood pressure to decrease in fit people.

Stomach Intestines
Because the body is pumping more blood to the muscles, it takes some away from the systems and functions that aren’t top priority at the moment, like digestion. That can result in tummy troubles. Movement, absorption and secretion in the stomach and intestines can all be affected.

Increased blood flow also benefits the brain. Immediately, the brain cells will start functioning at a higher level, says Cameron, making you feel more alert and awake during exercise and more focused afterward.

When you work out regularly, the brain gets used to this frequent surge of blood and adapts by turning certain genes on or off. Many of these changes boost brain cell function and protect from diseases such as Alzheimer’s, Parkinson’s or even stroke, and ward off age-related decline, she says.

Exercise also triggers a surge of chemical messengers in the brain called neurotransmitters, which include endorphins, often cited as the cause of the mythical “runner’s high.”

The brain releases dopamine and glutamate, too, to get those arms and legs moving, as well as gamma-aminobutyric acid, or GABA, a prohibitive neurotransmitter that actually slows things down, to keep you moving in a smooth and controlled manner.

You’ll also likely feel better thanks to a bump in serotonin, a neurotransmitter well known for its role in mood and depression.

This part of the brain is highly involved in learning and memory, and it’s one of the only sections of the brain that can make new brain cells. Exercise facilitates this, thanks to the extra oxygen in the brain.

Even when you stop exercising, those new brain cells survive, whereas many other changes in the brain during exercise eventually return to their normal state should you become less active.

The hypothalamus is responsible for body temperature, as well as salt and water balance, among other duties. As your body heats up, it tells the skin to produce sweat to keep you cool.

Pituitary Gland
This control center in the brain alerts the adrenal glands to pump out the hormones necessary for movement. It also releases growth hormones. As the body searches for more fuel to burn after using up your glycogen stores, it will turn to either muscle or fat, says Cameron. Human growth hormone acts as a security guard for muscle, she says, telling the body to burn fat for energy instead.

The rate at which the kidneys filter blood can change depending on your level of exertion. After intense exercise, the kidneys allow greater levels of protein to be filtered into the urine. They also trigger better water reabsorption, resulting in less urine, in what is likely an attempt to help keep you as hydrated as possible.

Adrenal Glands
A number of the so-called “stress” hormones released here are actually crucial to exercise. Cortisol, for example, helps the body mobilize its energy stores into fuel. And adrenaline helps the heart beat faster so it can more quickly deliver blood around the body.

As you pick up the pace, the body, like any engine, produces heat — and needs to cool off. The blood vessels in the skin dilate, increasing blood flow to the skin. The heat then dissipates through the skin into the air.

Eccrine Glands
At the hypothalamus’s signal, one of two types of sweat glands, the eccrine glands, get to work. These sweat glands produce odorless perspiration, a mixture of water, salt and small amounts of other electrolytes, directly onto the skin’s surface. When this sweat evaporates into the air, your body temp drops.

Apocrine Glands
This second type of sweat gland is found predominantly in hair-covered areas, like the scalp, armpits and groin. These sweat glands produce a fattier sweat, typically in response to emotional stress, that can result in odor when bacteria on the skin begin to break it down, according to the Mayo Clinic.

The capillaries close to the skin’s surface in the face dilate as well, as they strain to release heat. For some exercisers, this may result in a particularly red face after a workout.

Exercising puts extra weight on the joints, sometimes up to five or six times more than your bodyweight, says Laskowski.
Ankles, knees, hips, elbows and shoulders all have very different functions, but operate in similar ways. Each joint is lined with cushioning tissue at the ends of the bones called cartilage, as well as soft tissue and lubricating fluid, to help promote smooth and easy motion. Ligaments and tendons provide stability.

Over time, the cushioning around the joints can begin to wear away or degenerate, as happens in people with osteoarthritis, the most common type of arthritis.

Illustrations from Getty and by Jan Diehm for the Huffington Post.

Also on HuffPost:


  • Improved Sexual Function

    Here’s a motivating reason to get moving: regular physical activity can increase blood flow in a way that has a direct affect on sexual function, explains HuffPost blogger David Katz, M.D., founding director of Yale University’s Prevention Research Center At Griffin Hospital.

    In fact, a recent study published by Emory University researchers in the Journal of Sexual Medicine identified a link between physical activity and erectile function among men between the ages of 18 and 40.

    “The men in our study who exercised more seemed to experience a protective benefit against erectile dysfunction,” study co-author Wayland Hsiao, assistant professor of urology at Emory School of Medicine, said in a statement. “We hope that early screening for ED may be a gateway issue to help motivate young men to live healthily on a consistent basis so that they can possibly avoid health issues associated with a sedentary lifestyle, such as diabetes and cardiovascular disease. We see this as just the beginning.”

  • Changes In Gene Expression

    In the burgeoning field of epigenetics, scientists are discovering how environmental factors, including diet, stress and toxins, can change the way our genes are expressed, essentially turning certain genes on or off, and affecting which are passed down from generation to generation.

    One factor that can play a role? Exercise. Two recent studies have illustrated just how regular physical activity can affect gene expression.

    The first study, conducted by Swedish researchers illustrated how inactive young adults demonstrated an immediate shift in their muscle cells’ genetic material after just a few minutes on a stationary bicycle, HuffPost reported when the findings were released.

    The second study, conducted by researchers from the Harvard School Of Public Health, found that walking an hour a day can slash genetic tendencies toward obesity. We’ll walk to that!

  • Better Skin

    Sweating it out could help you get your glow on post-workout, too. As Dr. Katz explains, your skin is the largest organ in your body. And as we slough off tons of skin cells each day, we need to give our body the right construction materials — healthy foods, regular exercise, plenty of oxygen — to rebuild. ” If you’ve got good construction material,” he says, “you can build healthy skin cells and you have good skin.”

    Skin also tells the story of what’s going on inside your body. “The skin is the window dressing. It’s really reflective of overall health,” Katz says. And that means if your body’s natural detoxification system is healthy, including the kidneys, liver and spleen, it’ll translate into a healthy looking glow.

    Those body-sculpting benefits of working out don’t hurt either. “Skin draped over muscle looks great, skin draped over an excess of subcutaneous fat, not so much,” Katz says.

  • Healthy Eyes

    Here’s a health shocker: moving your feet may have health benefits all the way up to your eyes.

    According to a recent paper published in the journal Investigative Ophthalmology Visual Science, regular exercise may be linked to a lowered risk of developing glaucoma.

    Researchers, evaluating 5,650 men and women between the ages of 48 and 90, found that people who engaged in moderate physical exercise 15 years prior had a 25 percent reduced risk of low ocular perfusion pressure, a risk factor for glaucoma.

    “It appears that OPP is largely determined by cardiovascular fitness,” author Paul J. Foster, M.D. Ph.D., of the University College London Institute of Ophthalmology said in a statement. “We cannot comment on the cause, but there is certainly an association between a sedentary lifestyle and factors which increase glaucoma risk.”

  • Better Sleep

    Breaking a sweat during the day may just mean better beauty sleep at night. According to a large study published last year in the journal Mental Health and Physical activity, people who exercised at a moderate or vigorous level for at least 150 minutes a week (that’s just over 20 minutes a day) reported 65 percent better sleep quality than their more sedentary peers.

    “Increasingly, the scientific evidence is encouraging as regular physical activity may serve as a non-pharmaceutical alternative to improve sleep,” study author Brad Cardinal, a professor of exercise science at Oregon State University said in a statement when the findings were released.

    And that, in turn, could have a whole host of additional benefits, as poor quality sleep has been linked to increases in inflammation, high blood pressure, and increased blood glucose levels in people diagnosed with Type 2 Diabetes.

  • A Sharper Brain

    Looking at your body holistically, what’s healthy for the whole body — good nutrition, plenty of rest, supportive relationships — is also good for the brain, explains Katz. And the same goes for regular exercise.

    “If something is good for your brain, it’s probably good for you,” he told The Huffington Post. “And if it’s not good for you, it’s probably not good for your brain.”

    In the short term, exercise means increased blood flow to the brain, which can help you stay sharper. So instead of taking that coffee break, which provides an artificial stimulant to help you focus in the short-term, consider a walk instead. “Exercise does the same thing and it confers a lasting benefit into the bargain,” he says. (Added bonus: sitting for too long has been associated with a host of health problems, including increased diabetes and cancer risk.)

    In fact, one Swedish study published last year in the Journal of Occupational and Environmental Medicine found that taking exercise breaks at work for two-and-a-half hours a week was associated with improvements in productivity.

    Physical fitness also has brain benefits in the long term, as well. Studies have linked regular activity to decreased risk of dementia and improved memory.

  • Fewer Migraines

    Roughly 36 million people in the United States suffer from migraines, according to the Migraine Research Foundation — and the oftentimes debilitating headaches take their toll in more than 113 million lost work days each year.

    Characterized by intense pain in one side of the head and often joined by symptoms of nausea, vomiting and sensitivity to light and sound, migraines tend to run in families and are triggered by a variety of factors, from foods to stress to environmental changes, according to the Mayo Clinic.

    Treatments can include drugs taken at the onset of an attack and preventive medications — and a recent, small study suggests that exercise may be just as effective at the latter.

    The findings, published in the journal, Cephalalgia, suggest that regular physical activity may be able to prevent migraines as well as drugs or relaxation therapy, The Huffington Post reported when the study was released last year.

  • Boosted Immunity

    The brunt of flu season may be behind us, but regular, moderate exercise may help us to stave off a springtime cold by upping the body’s defenses against viruses and bacteria.

    A sedentary person is likely to catch two to three upper respiratory tract infections each year, HuffPost reported earlier this year, but a moderately active person can cut that number by close to a third.

    But the effect reverses in the case of intense exercise — marathoners, for instance, may have a two-to-six-fold increase in contracting an upper respiratory tract infection in the weeks following a race.

  • A Sunnier Disposition

    As much as we all sometimes dread the prospect of working out, the truth is that you’ll actually feel better after you’re done. Physical activity triggers the release of endorphins, those feel-good chemicals that produce a sense of euphoria in the brain. (Who can forget the famous Legally Blonde quote: “Exercise gives you endorphins. Endorphins make you happy. Happy people just don’t shoot their husbands, they just don’t.” Just us?)

    Recent research has further confirmed the link between working out and happiness — last month, Penn State researchers published findings suggesting that people who are more physically active reported greater general feelings of excitements and enthusiasm, The Huffington Post reported when the study was published.

    “Our results suggest that not only are there chronic benefits of physical activity, but there are discrete benefits as well,” study researcher Amanda Hyde, a kinesiology graduate student at Penn State, said in a statement. “Doing more exercise than you typically do can give you a burst of pleasant-activated feelings. So today, if you want a boost, go do some moderate-to-vigorous intensity exercise.”

  • More Birthdays

    Could daily workouts be the real fountain of youth? Maybe so.

    A Taiwanese study published last year in The Lancet suggests that even just 15 minutes of physical activity a day can  extend life expectancy by three years, compared to people who didn’t exercise.

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