How long you exercise at your target heart rate depends on whether you're working out for heart health, weight loss or athletic performance. Beginners, intermediates and athletes use different heart rates to achieve different goals, with exercises and workouts lasting anywhere from 30 seconds to an hour. Whether you're exercising once a day or performing two or three daily workouts also factors into your target heart rate goals.
Target Heart Rate
Your target heart rate is actually a heart rate range in which you seek to exercise to meet certain fitness goals. For example, if you are an athlete who wants to improve anaerobic fitness, you might train using an intensity that puts you at a number of heart beats per minute that is 80 to 90 percent of the maximum heart rate you can sustain. If you are interested in weight loss, you might exercise in a commonly recommended target heart rate range that keeps you between 70 and 80 percent of your maximum heart rate. To maintain your heart health, you can exercise at your weight-loss target range, or exercise at 50 to 65 percent of your maximum heart rate, depending on how long you can work out.
Length of Exercise
If your goal is improved heart health and weight maintenance, you should exercise at a moderately intense heart rate, which is similar to what you achieve during a brisk walk, for 150 minutes per week, according to the American Heart Association. The association recommends five 30-minute workouts each week, but notes that three 10-minute workouts, or two 15-minute workouts each day at this heart rate provides many of the same benefits. If you exercise at a vigorous heart rate, such as at a jogging pace, you need 75 minutes of exercise each week. To lose weight, you'll need to increase your exercise time. If you are an athlete doing sprint training, your exercises should last 30 to 120 seconds, followed by two to three minutes of recovery at a walking speed. Your workouts might last only 10 to 15 minutes.
If your exercise goal is calorie burning, the length of your workouts will depend on your heart rate and calorie goals. Using a heart rate monitor or information you get from an online calorie calculator can help you to stay in your target heart rate range long enough to burn a specific number of calories. For example, a 125-pound woman who wants to burn 400 calories using a rowing machine will need to exercise for just under an hour at a moderate heart rate, or approximately 45 minutes at a vigorous heart rate, according to the Harvard School of Public Medicine.
If you are new to exercise, your goal should not be to exercise at a high heart rate to maximize calorie burn per minute, but rather to build cardio strength, stamina and muscular endurance, so that after two or three weeks, you will get in shape to perform longer, high-intensity workouts that burn maximum calories. You'll exercise in a lower target heart rate range, such as 50 to 65 percent of your maximum heart rate range, so that you can exercise for 30 to 60 minutes.
Calculating Target Heart Rate
For many years, health professionals recommended that men and women subtract their age from 220 to get an approximation of their maximum heart rate. Using this formula, you multiply maximum heart rate by your desired workout heart rate intensity to get your target heart rate. For example, if you are 30 years old, subtract 30 from 220 to get 190, then multiply it by .70 and .80 if you want to exercise in the common aerobic heart rate range. This 220-minus-age formula is too high for women, however, according to Northwestern Medicine researchers who studied more than 5,000 women in 2010. They found that women should multiply their age by .88, then subtract this number from 206 to get a more accurate maximum heart rate. A 30-year-old woman who wanted to exercise at 70 to 80 percent of her target heart rate would work out between 126 and 144 beats per minute using this formula. Using the old 220-minus-age formula, she would have to exercise between 133 and 152 beats per minute.