Do I Burn Less Fat if My Heart Rate Is Too High While Exercising?

The target zone has become a buzz word for people wanting to lose weight through exercise. Many trainers advise exercising at a lower intensity to burn more fat. This is only partly true. When your heart rate is lower, your body uses a greater percentage of fat as an energy source. But at a higher intensity, you'll burn more calories overall.

Wearing a heart rate monitor is an easy way to check your exercise intensity. (Image: Jupiterimages/Photos.com/Getty Images)

Aerobic Exercise

When you exercise at low intensities, fat accounts for most of your energy expenditure. As your heart rate increases, you burn a higher percentage of carbohydrates. According to the American Council on Exercise, higher-intensity exercise will result in greater weight loss. It doesn't matter whether your body is burning carbohydrates or fat. In addition, a higher intensity will keep your metabolism elevated for longer, so you'll burn additional calories even after you stop exercising.

Reaching Lactate Threshold

Your lactate, or anaerobic, threshold is the point where your body can't supply adequate oxygen to your muscles. After this point your body burns carbohydrates exclusively. High intensity workouts are effective for burning a large number of calories quickly. However, lactic acid begins to build up in your blood, your muscle carbohydrate stores begin to get depleted and you might fatigue rapidly. Sports coach Brian Mac says your lactate threshold may be between 50 and 90 percent of your maximum heart rate, and increases with training.

Calculating Target & Maximum Heart Rates

You can estimate your maximum heart rate by subtracting your age from 220. For example, if you're 40, your MHR is roughly 180. The Cleveland Clinic advises that you'll gain most benefits from exercise at between 60 and 80 percent of this rate. Avoid exceeding 85 percent, as this can cause added cardiovascular risks. When exercising, stop occasionally and measure your pulse by pressing two fingers lightly on your wrist. Count the number of beats for 30 seconds and multiply by 2. Alternatively, wear a heart rate monitor to measure your intensity of exercise.

Exercising To Lose Weight

Perform 150 minutes of moderate aerobic activity per week to stay fit. If you're trying to lose weight, you increase the amount of time you exercise. One option for maximizing fat loss is interval training. Alternate five minutes of vigorous exercise at the higher end of your target zone, with two minutes at a lower intensity. Another good option is running or cycling for longer periods at a low to moderate intensity. If you're not used to exercising, build up to your target rate gradually. If you have a heart condition or other health problems, consult your doctor before beginning an exercise routine.