1. You burn calories.
When your body breaks down energy-dense foods, like carbs and fats, it turns them into the molecule ATP (adenosine triphosphate). Then, when the body converts ATP into ADP (adenosine diphosphate), it gives off energy and allows muscles to contract and move. It’s what we mean when we say we’re “burning calories,” says Joseph E. Herrera, DO, chair of the Department of Rehabilitation Medicine for the Mount Sinai Health System.
2. You heat up.
As your body burns calories, its temperature rises, and you sweat. “Sweat wicks away heat, which allows your body to keep working out without overheating,” says Herrera.
3. Your heart beats faster.
Exercising raises your heart rate in order to quickly push blood and oxygen to the muscles. If you train for endurance events often, your resting heart rate may get lower, says Herrera, as your heart becomes more efficient at supplying blood to your organs and muscles.
4. Digestion can turn wonky.
Ever felt like you suddenly had to go to the bathroom after starting a run? Blood flow is directed away from your core and intestines to your large working muscles, which can lead to diarrhea. Tip: Avoid food an hour before exercise.
5. Happy hormones flow.
At the start of a tough workout, you get a spike in adrenaline and the stress hormone cortisol. Your body senses you’re in “flight” mode (i.e., trying to escape a threat). Next, endorphins help cut muscle pain and improve mood. Other compounds, called endocannabinoids, may also be partly responsible for that “runner’s high,” according to animal research.
6. Your brain gets a boost.
Aerobic activity improves our thinking skills and memory, possibly because there’s increased blood flow to the brain during exercise. Getting active may also promote brain growth.
7. Muscles get stressed (in a good way).
Each time a muscle is challenged, micro tears occur, says Herrera, but they aren’t harmful; they contribute to muscle growth over time.
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