Is High-Intensity Exercise Always Best?

Getting fit is all about getting started with moving your body. And it's not just about how much movement and what type of movement you do—it's also about how intensely you do that movement. Exercise and physical activity are generally categorized into three different types of intensity: low, moderate, and high (sometimes called "vigorous"). But it can be tricky to understand exactly what type of activity falls into which intensity bucket.

For example, the World Health Organization's (WHO) 2020 guidelines on physical activity and sedentary behavior recommends 150 to 300 minutes of moderate-intensity exercise per week (that's about 21 to 43 minutes per day) or 75 to 150 minutes of vigorous-intensity aerobic exercise per week for able-bodied adults. But how do you know for sure that your movement of choice really is vigorous enough? Is your level of aerobic activity too vigorous? Is high-intensity always best, or will a good low-impact walk get the job done? Do the same guidelines apply to both beginners and fitness buffs? So many questions.

Knowing what each exercise intensity means and learning how to structure your fitness routine accordingly will help you get the most from the exercise you do. We asked health and fitness experts to break them down, explain why they matter, and share how to apply them to your daily life.

An Overview of Exercise Intensity

Intensity correlates with how hard you're working—or really, how hard your heart is working—when you exercise. The three levels progress from easiest to hardest, and there are two ways to measure them, either the "talk test" or by measuring heart rate.

The talk test is probably the easiest way to measure intensity, since you only need to figure out how easy or hard it is to talk during whatever activity you're doing. With low intensity, you're moving, but you're still able to be conversational, says William Smith, MS, NSCA-CSCS, author of Exercises for Cardiac Recovery.

When you move into moderate-intensity activity, while you shouldn't be totally out of breath, you won't be able to hold a conversation as easily. Your sentences may be slightly broken up with intermittent, yet manageable, heavier breathing. If you're moving with high or vigorous intensity, you won't be able to carry on a conversation at all (nor will you want to).

Exercise intensity can also be determined more technically by heart rate: how frequently your heart is pumping in the span of a minute (aka beats per minute). Heart rate monitors make measuring your resting and working heart rate a simple task (smartwatches like the Apple Watch often have this handy function). If you don't have a monitor, however, you can do some old-school counting. Just find your pulse on your wrist or neck and count the number of beats for 10 seconds; then multiply that number by six for beats per minute.

Understanding Maximum Heart Rate and Workout Intensity

Knowing all this, the next step is to calculate your maximum heart rate (MHR): the highest point of intensity that you should be achieving during exercise.

"Exercise intensity is calculated as a percentage of your maximum heart rate during physical activity," says Ben Walker, a personal trainer and owner of Anywhere Fitness in Dublin, Ireland. "The higher the percentage, the harder your body is working."

To determine what your body's maximum heart rate should be, subtract your age from 220.

For instance, if you're 40 years old, your estimated MHR would be about 180 beats per minute. Now, once you know your personal MHR, you can use it to measure how many beats you should be striving for during activities, depending on their intensity. Here's a breakdown:

Low Intensity

Low intensity is calculated as working at about 30 to 50 percent of your MHR. Multiply your MHR by .30 and then .50 to determine your heart rate range, Walker says.

Sticking with the example above, if you're 40 years old with an estimated MHR of about 180 beats per minute, multiply 180 by .30 (=54) and then .50 (=90). The result? A hypothetical, healthy 40-year-old's heart rate should remain roughly between 54 and 90 beats per minute when engaging in low-intensity exercise. Low-exertion aerobic activity can often involve moving repetitively at a slower, steadier pace: casual walking (where you can still hold a conversation), light yoga, biking at low-resistance, or leisurely swimming laps. You're moving, but you're not huffing and puffing.

Moderate Intensity

With moderate-intensity aerobic movement, your heart will work a bit harder—though not at max capacity—at roughly 50 to 70 percent of your MHR. Common activities include brisk walking or hiking, aerobic dancing, doubles tennis, cycling (slower than 10 miles per hour, according to the American Heart Association), and even vigorous yard- or housework.

High Intensity

Finally, high intensity means you're training at 75 to 100 percent of your MHR (the average 40-year-old's heart should be pumping at 135 to 180 beats per minute). This vigorous type of movement often involves short, quick-burst exercises where you're fast off the mark, Walker says. You should be working hard, breathing rapidly and heavily, getting sweaty, and unable to sustain a conversation. You might, for instance, be jumping rope, running the stairs, doing a HIIT (high-intensity interval training) workout, playing singles tennis, running, or cycling 10 miles per hour or faster.

Benefits of Each Exercise Intensity Level

Each exercise intensity affects the body differently. While they all have benefits, how much you do of each one will largely depend on your current fitness level and goals.

Low Intensity

Beginners should start with low intensity, which is beneficial not only for fitness novices, but also seasoned athletes. Think of low-intensity exercise as building the groundwork for more intense exercise.

"Low-intensity exercise reduces the risk of injury while preparing your body for more intense activities," Walker says, adding that it primarily burns fat cells as a fuel resource. It also builds your stamina, which you'll need as you progress in your fitness program since it activates the aerobic system. It's also crucial for sports-specific athletes. "If you're training for any sport that requires a lot of movement for longer spells, you'll need to train aerobically to handle this required level of fitness."

Moderate Intensity

When you shift into moderate-intensity exercise, your body begins using fat, carbohydrates, and sugar as fuel sources. "Burning calories from all of these sources help achieve quicker weight loss results," Walker says. More moderate-level activity is needed to achieve more health benefits (the higher the intensity, the less time is needed to reap those exercise rewards).

High Intensity

As soon as you move into high-intensity exercise, though, you're exercising to your full potential. Not only does this stimulate the best response in your body for fat loss and muscle gains, it also boosts your metabolism for hours after your workout. "By training at maximum capacity, you increase potential for muscle growth and weight loss by breaking down more muscle fibers," says Walker, adding that it's a fantastic way to maintain lean muscle mass and improve body composition.

Applying It to Your Fitness Routine

So how do you know what intensity you should hit during exercise? While it will depend on your health, current fitness level, and personal goals, some guidelines can help. (Note: Definitely talk to your doctor if you have any questions or concerns about the right intensity for you and your health.)

According to the 2018 Physical Activity Guidelines for Americans, and echoing WHO global guidelines, adults should get at least 150 to 300 minutes of moderate-intensity activity, 75 to 150 minutes of vigorous-intensity exercise, or a combination of each every week. (Guidelines also suggest that you do muscle-strengthening activities at least two days a week.) Even the American Heart Association and American College of Cardiology have exercise prescriptions, namely recommending 30 minutes of moderate-intensity exercise five to seven days a week, says Waqar Khan, MD, a board-certified interventional cardiologist in Houston, Texas and author of Be Heart Smart.

Of course, if you're just beginning an exercise program, always start with low-intensity exercise and progress gradually, Walker says. This also applies if you're recovering from an injury or health issue like a heart attack, Dr. Khan adds.

Once you get past this point, your personal goals will largely dictate your exercise program and how intense your workouts are. If you're hoping to achieve optimal health, follow the above guidelines. If, however, you have sport-specific goals, you may need something different.

The one caveat? While high-intensity exercise can be good for the body, your heart included, you don't want to overdo it. Extreme aerobic exertion is taxing on the body, which also needs time to recover from it. Walker suggests doing no more than three high-intensity workouts each week, spaced a day apart.

On the flip side, unfortunately, long hours of low-intensity exercise won't add up to the same benefits as vigorous-intensity activity (or even moderate). The two intensity levels stimulate different reactions in the body, Walker says, and if you do excessive amounts of low-intensity exercise, while you may improve your cardiovascular health, you risk depleting your muscle tissue.

The most important takeaway though is not to get so hung up on the numbers—find the motivation to get up and move regularly, however you can. Intensity aside, all movement matters.