Exercise Intensity and How to Use It

How to make your workouts as effective as possible.
Published January 25, 2018

If you’ve been exercising for a while—at least a few months—you’re consistent with your workouts, and would like to see continued results, you may be ready to increase intensity during your sessions. Now don’t be scared off by the “I” word, because intensity, when understood and used appropriately, can be quite effective for not only weight loss, but also for boosting health.

Ways to Measure Exercise Intensity

Knowing how to monitor intensity will help ensure that you’re using this training tool most effectively. “There are two common ways to measure exercise intensity the most common of which is heart or pulse rate: the higher the intensity effort, the higher the heart rate,” explains Walt Thompson, PhD, president of the American College of Sports Medicine and Associate Dean for Graduate Studies and Research at Georgia State University. To measure heart rate, you can count how many times your heart beats in 30 seconds and multiply it by two for your beats per minute, or you can wear a heart rate monitor, which will provide continuous readings throughout your workout.

The second way to measure intensity is based on how you feel, which is called the rating of perceived exertion, or RPE. With RPE, you assign a number to how hard you feel you’re working; a higher number corresponds with higher intensity, and thus a higher heart rate. “The original Borg scale started at six and went to 20 and, if multiplied by 10, any rating would approximate heart rate,” explains Thompson. “The more common scale is zero to 10, with zero being no effort and 10 being maximal effort. Moderate effort would be around a 7 to 8.” A simpler, albeit less scientific method measures intensity on a scale of 1 to 4, which corresponds with levels of exercise that are mild, moderate, severe, and exhaustive.

When to Use the Different Exercise Intensities

Every exercise session shouldn’t be at the same level of intensity each time. Alternate days of lower intensity exercise, such as walking around the block or going for an easy bike ride, with higher intensity activities other days of the week.

Mild: Exercise performed at levels that range from 0 to 6 (6 to 12 on the Borg scale) is considered mild to moderate activity. This is also known as the fat-burning zone: where your body burns primarily fat for energy instead of the glycogen (stored carbohydrate) circulating in your blood and stored in your muscles and liver. However, to tap into fat stores, you need to exercise continuously for a minimum of 30 minutes. Mild exercise is a good option when you are experiencing some muscle soreness, or the day after a particularly difficult workout, or when you just want to move.

Moderate: If you’re exercising at a 7 to 8 (13 to 16 on the Borg scale), your breathing is heavy, your heart rate is up, and it’s a challenge to talk. This is the zone where your heart becomes stronger and you see improvements in your cardiovascular health. Sometimes this is called the cardio zone.

Hard to Exhaustive: A challenging workout, where the intensity makes talking difficult because you’re breathing hard and your whole body feels fatigued, is considered high-intensity and around a 9 (17 to 18 on the Borg scale). Going even harder, a level 10, is extremely difficult and at maximum exertion. Recently, scientists have found that working at even these supreme levels have benefits; however, exercise at this intensity should only be done in short bursts.

Why Do High-Intensity Exercise

Studies have shown that high-intensity exercise can help control blood glucose levels, improve cardiovascular fitness, and reduce blood pressure. According to Thompson, another benefit of using intensity in your workouts is the time you save.

“Workouts can be shorter in duration,” explains Thompson. “A busy person can get the same benefit with a higher-intensity, shorter-duration exercise program when compared to the lower-intensity, longer-duration program.” And as you get stronger and are able to maintain higher intensity over a longer period of time, the benefits will keep coming.

Not many years ago, high-intensity interval training, aka HIIT, was something done only by athletes who were looking for a sports performance edge. During HIIT, short bouts of severe and exhaustive intensities are reached and separated with mild intensity exercise. However, times have changed. “The latest scientific literature on the topic of high intensity interval training seems to suggest that many populations can benefit from increasing intensity,” explains Thompson. “There is now less fear of increasing injury rates with high-intensity interval exercise.”

However, he warns that people who haven’t engaged in high-intensity exercise should work with someone who knows what he or she is doing. “Work with someone who has the education, training, and experience with this kind of activity,” such as an American College of Sports Medicine certified fitness professional who can offer the best advice and answer any questions you may have as you begin to incorporate this type of training into your workout program.

Before adding high-intensity exercise to your workout routine, get the green light from your physician. Also be conservative and build intensity slowly, over a period of weeks. If during a workout you begin to feel lightheaded, feel chest pain or shortness of breath or feel your heart is beating uncontrollably, stop the workout and make a call to your doctor.

Ultimately, no single intensity and no single activity is better than the other. Physical activity of various intensities and durations all lead to weight loss. The best workout is the one you enjoy and will keep you moving regularly.