Exactly What Exercise Intensity Has to Do with Weight Loss

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.

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.

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), you’re 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 is 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.