Are you a cardio junkie? Maybe you like to run laps at a local track. Or walk a route around your neighborhood. Maybe you test your mettle on a grueling bike ride. Or challenge your endurance on the elliptical. Every one of them will get your heart pumping.

But what’s going on inside your body when you’re working up a sweat?

Cardiovascular exercise is any type of repetitive motion using large muscles that increases your heart and breathing rate. Blood flow is directed to the muscles doing the work (like your legs) and away from the ones not doing work (like your arms or small muscles inside your digestive tract).

Over time, regular cardio causes your resting heart rate to drop because your left ventricle adapts to the larger blood volume and it gets bigger. With a larger and stronger muscle, more blood is pumped per beat, even at rest, so your heart doesn’t have to work as hard. This is what makes cardio exercise so good for your heart.

On the flip side, too much of anything is rarely good.

If you do too much cardio, you can become overtrained. Overtraining can create more stress than your body can handle. It can lead to sickness, injury, the release of stress hormones, even weight gain. So while you do cardio to become more fit, reduce stress and lose weight, too much cardio can derail your efforts.

Most Americans are not in danger of that, though. Few of us get the recommended amount of exercise per week, which is only 150 minutes. We can do better.

Breaking that 150 minutes into 10-minute chunks of time makes it manageable for even the busiest people. It’s so worth it. People who are physically active tend to live longer and have lower risk for heart disease, stroke, Type 2 diabetes, depression, and some cancers. Physical activity can also help with weight control, and may improve academic achievement in students.

So what are you waiting for? Lace up those sneakers and go for a walk.

Source: Exercise and the Heart,  John Hopkins Medicine, 2023

Originally published 5/1/2017; Revised 2021, 2023