Cardio exercises are any activities that raise your heart rate and keep it elevated long enough to challenge your heart, lungs, and circulatory system. Running, swimming, cycling, and brisk walking all qualify, but so do rowing, jump rope, dancing, and dozens of other movements. What makes an exercise “cardio” isn’t the specific movement. It’s the sustained demand on your body to deliver oxygen to working muscles over time.
How Cardio Works in Your Body
When you start a cardio workout, your muscles need more energy than they do at rest. To meet that demand, your body ramps up a process called oxidative metabolism, which takes place inside tiny structures in your cells and produces large amounts of fuel using oxygen. This is why breathing gets heavier and your heart beats faster: your body is working to pump more oxygen-rich blood to the muscles that need it.
The key measure here is cardiac output, which is simply how much blood your heart pumps per minute. As your workload increases, your heart rate climbs and each beat pushes out more blood. Your nervous system releases stress hormones that widen blood vessels around the heart and working muscles, directing flow where it’s needed most. Over weeks and months of regular cardio, your heart becomes more efficient at this entire process. It pumps more blood per beat, your resting heart rate drops, and your muscles get better at extracting oxygen from the blood.
Common Types of Cardio
Cardio exercises generally fall into two categories based on joint impact, and knowing the difference helps you pick activities that match your body and goals.
High-Impact Cardio
These involve running, jumping, or movements where both feet leave the ground. Examples include running, jumping rope, tennis, CrossFit-style workouts, hiking on uneven terrain, and ballet. High-impact cardio strengthens bones and increases bone density more effectively than low-impact options, which matters for long-term skeletal health. The tradeoff is greater stress on joints, particularly knees, hips, and ankles.
Low-Impact Cardio
Low-impact exercises keep at least one foot on the ground (or take your feet out of the equation entirely). Swimming, walking, cycling, elliptical training, and rowing all fit here. These are easier on joints, making them a strong choice if you have arthritis or are returning from injury. Low-impact does not mean low-intensity. Swimming laps vigorously or cycling at a fast pace can push your heart rate just as high as running. The difference is mechanical stress on your body, not the cardiovascular challenge.
Calories Burned by Activity
How many calories you burn during cardio depends on the activity, your intensity, and your body weight. Harvard Health Publishing estimates the following for 30 minutes of exercise at a body weight of about 155 pounds:
- Brisk walking (3.5 mph): ~133 calories
- Running (5 mph / 12-minute mile): ~288 calories
- Running (7.5 mph / 8-minute mile): ~450 calories
- Cycling (12–14 mph): ~288 calories
- Cycling (16–19 mph): ~432 calories
- Swimming (general): ~216 calories
- Swimming (vigorous laps): ~360 calories
A lighter person (around 125 pounds) burns roughly 20–25% fewer calories at the same pace, while a heavier person (around 185 pounds) burns about 15–20% more. Speed matters too. Doubling your running pace from a slow jog to a fast run can nearly double your calorie expenditure in the same half hour.
Steady-State vs. Interval Training
You’ll often hear about two broad approaches to cardio: steady-state and high-intensity interval training (HIIT). Steady-state means maintaining a consistent moderate pace for the duration of your workout, like jogging at the same speed for 30 minutes. HIIT alternates short bursts of near-maximum effort with recovery periods, such as sprinting for 20 seconds then resting for 10.
Research comparing the two approaches has found that both produce similar improvements in aerobic fitness. In one study, all groups (steady-state, moderate intervals, and intense Tabata-style intervals) improved their maximum oxygen capacity by 18–19% over the training period. Both approaches also improved power output and anaerobic performance by comparable amounts.
The practical difference comes down to time and recovery. HIIT sessions are shorter but significantly more demanding. In that same study, participants doing Tabata-style intervals were still visibly exhausted after their cooldown and needed extra time before they could resume normal activities. Steady-state exercisers were fully recovered by the end of their cooldown. If you enjoy pushing hard and want shorter workouts, HIIT works well. If you prefer a more sustainable pace or are newer to exercise, steady-state cardio delivers the same fitness gains with less post-workout strain.
Heart Rate Zones
Your heart rate is the simplest way to gauge how hard you’re working during cardio. To find your approximate maximum heart rate, subtract your age from 220. A 40-year-old, for example, has an estimated max of 180 beats per minute.
The American Heart Association defines two main training zones based on that number. Moderate intensity sits at 50–70% of your max, which for a 40-year-old means 90 to 126 beats per minute. Vigorous intensity falls between 70–85% of max, or 126 to 153 beats per minute for the same person. You don’t need a heart rate monitor to gauge this. At moderate intensity, you can hold a conversation but not sing. At vigorous intensity, you can only get out a few words before needing a breath.
How Much Cardio You Actually Need
The World Health Organization recommends adults aged 18 to 64 get at least 150 minutes of moderate-intensity cardio per week, or 75 minutes of vigorous-intensity cardio, or some combination of both. That works out to about 30 minutes of brisk walking five days a week, or 25 minutes of running three days a week.
For greater health benefits, doubling that to 300 minutes of moderate activity per week is the next target. The WHO also recommends strength training involving major muscle groups on two or more days per week, which complements cardio rather than replacing it.
What Cardio Does for Your Health
The cardiovascular benefits are the most direct. Physically active people have a 21% lower risk of developing cardiovascular disease and a 36% lower risk of dying from it compared to inactive people. Regular cardio lowers resting blood pressure by an average of 3 to 4 mmHg (both the top and bottom numbers) and reduces LDL cholesterol by 3 to 6 mg/dL. Those numbers sound modest, but at a population level they translate into meaningfully fewer heart attacks and strokes, and the benefits compound over years of consistent activity.
Beyond the heart, regular cardio improves insulin sensitivity, supports weight management, strengthens respiratory function, and improves sleep quality. The mood effects are well established too. Sustained aerobic activity triggers shifts in brain chemistry that reduce anxiety and improve emotional regulation, often noticeable within the first few sessions.
Choosing the Right Cardio for You
The best cardio exercise is one you’ll actually do consistently. But a few practical factors can help you narrow it down. If joint pain or arthritis is a concern, start with low-impact options like swimming, cycling, or the elliptical. If building bone density is a priority, high-impact activities like running or jumping rope provide a stronger stimulus. Rowing machines and ellipticals engage your arms, legs, and core simultaneously, making them efficient full-body options when time is limited.
If you’re new to cardio or returning after a long break, start with moderate-intensity sessions of 15 to 20 minutes and increase duration before intensity. Mixing high-impact and low-impact days throughout the week gives your joints recovery time while still building fitness. Many group fitness classes, including dance-based formats like Zumba, offer low-impact modifications alongside the standard moves, so you can adjust on the fly.