What Happens in Your Body When You Workout?

Aerobics and muscle-building routines will make you stronger and happier. The hardest part is getting started. Here’s how you can.

For most of us, the first moment of aerobic exercise feels tough. Your heart speeds up, you breathe slowly, and you might stiffen.

Your body responds to exercise with a series of changes to make you stronger. We developed those survival responses back when we watched the sky for buzzards and had to outrun them to reach the juicy meat in a carcass before it was picked clean. Now that steaks are sold at the supermarket, you won’t go hungry because you don’t have to run. But you’ll be healthier if you keep your body as close to savanna-ready as you can. 

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What happens in your body when you workout?

When you’re exercising, let’s say running, some parts of your system shut down while others work harder. Your heart beats faster to pump blood to your muscles. Your digestion slows. Your body increases oxygen flow and releases heat and other byproducts.

For the most intense movement — throwing a punch, lunging, sprinting — your body will supply all of your cells with several seconds worth of a fuel called “ATP.” 

Beyond those first few seconds, your muscles will tap into stores of glycogen, a substance that converts to ATP over a minute and a half. Lactic acid builds up in your muscles, creating an exercise burn.

After around two minutes, your body responds, increasing your access to oxygen. Now you’re getting aerobic exercise. Oxygen helps you turn glycogen into glucose or draw glucose from your blood or food in your intestines.

To take in more oxygen, your lungs work more quickly. The fitter you are, the more oxygen you’ll get. To move the oxygen through your body, your heart rate increases along with your blood flow.

Your heart is a muscle that gets bigger and more efficient with training. Top athletes can pump more than twice as much oxygen-rich blood per heartbeat than the average adult. So, their hearts don’t need to pump as hard for the same amount of exercise and, at rest, may beat as little as 40 times per minute, compared to the average of 60 to 80.

As you workout, heat builds inside your body. Your blood vessels dilate to bring heat towards your skin and release it into the air, making your skin feel warm. Your face might turn red as well. Tiny tears occur in your muscles, making you sore. As the tears heal, you get stronger. 

The whole experience is good for your brain, which releases feel-good chemicals in response. You’ll feel more alert and focused. 

Aerobic exercise is a goldmine of health benefits. It helps:

• Pull you out of bad moods and fight mild depression
• Maintain a normal weight and avoid the many risks associated with obesity
• Prevent heart disease, lowering blood pressure and making your blood vessels less likely to get clogged with fat

Keep your body responsive to insulin — staving off diabetes, a condition in which you need extra insulin to maintain the right blood sugar levels

Exercise also helps prevent dementia and slow milder mental decline with age. 

How much exercise do you need?

Adults need at least 150 minutes a week of some kind of moderate exercise. Exercise is moderate if you need to breathe faster.

In a large study of more than 270,000 older men, running and racquet sports, followed by walking for exercise, cut the risk of dying over the next 12 years most dramatically, but any exercise helped. Even just an hour a week of physical activity cut death risk by 18 percent in other research.

Are you worried about cancer? In a 10-year study, regular physical activity lowered the risk of colon, breast, kidney, and liver cancer. 

If exercise is new to you, walking may be the best way to start. Aim to build up to about an hour a day. You could reduce your death risk by 39 percent.

Build muscle, too

Don’t neglect strength-training. Lifting weights is one way to do it; you can also do resistance training exercises. Either can prevent falls and injuries, especially as you age, and make it more fun to engage in sports or play with your kids and grandkids. In addition, building muscle will help you burn fat, the most important part of maintaining a healthy weight.

Staying strong can also keep you alive. In a meta-analysis of 10 studies researchers found that any amount of resistance training cut death risk by 15 percent, and death from cardiovascular disease by 19 percent.

For the maximum benefit — lowering your risk of death by 27 percent — you need about an hour a week of strength training.  

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