Confused About My Heart Rate

Q. Heart-rate calculators indicate that my target heart rate during exercise should be around 140 beats per minute since I am 47 years old. At what point should my heart rate reach this number? Should it stay consistent at 140 from the start to the end of my run, or is there a certain period during which it should be at this level?

A. Your heart rate is a reflection of the intensity at which you are exercising. You can track it by wearing a heart-rate monitor or using the heart-rate reader on a cardio machine. Or you can pause during a workout and measure it yourself (although this takes practice).

But before you worry about what your heart rate should be,  you first need to determine your fitness status and your fitness goals.

• Are you a new or long-time runner?
• Are you running for the fun or it, or for stress release?
• Are you running races?
• Are you trying to lose weight?
• Or are you running so that you can eat dessert guilt-free?
• Are you trying to improve your cardiovascular fitness in a measurable way (i.e. increase your V02 max—or your body's maximal oxygen consumption, which is an indicator of how fit you are)?

Your answers to these questions will determine what heart rate you may want to aim for—or whether you need to monitor your heart rate at all.

To take your heart rate or not?

If you are a new exerciser, taking heart rates may be useful because it can prevent you from overexerting yourself. If you're a healthy, regular, recreational runner, and you're not trying to beat any world records, you probably don't need to worry about your heart rate. If you take a more serious approach to your workouts and like to push yourself, gauging your heart rate can be a motivational training tool.

But keep in mind that you don't need to take your heart rate to know what your effort level is or to train at different intensities. You can also monitor your intensity in other ways such as using your rating of perceived exertion. For example, you might do a sprint that feels very hard for 30 seconds, then walk for two minutes at a pace that feels somewhat hard.

Or you can run at a speed that makes you feel breathless for one minute, then recover by jogging or walking at an easier speed during which you're still able to belt out a song. Some people think that heart rates are more accurate than RPEs, but that's not necessarily true, especially for regular exercisers.

What should my heart rate be?

Various heart-rate calculators recommend target heart rate ranges depending upon your age, and the numbers can vary depending upon the target ranges chosen.

The American College of Sports Medicine suggests that a broad range of exercise intensities will produce cardiovascular improvements. Depending on your fitness level, your heart can get stronger if you work out at an intensity that is as low as 40 to 50 percent of your maximum heart rate, or as high 85 to 90 percent of your maximum heart rate.

The most recent 2007 ACSM physical activity guidelines recommend working out at a "moderate" to "vigorous" intensity to promote and maintain health. Those wishing to improve their fitness or further reduce their health risks should exceed the minimum amounts of suggested activity. In other words, any exercise is good for you, but the harder you push yourself and the more often you exercise, the more benefit you will get.

If you are trying to increase your cardiovascular endurance, power and/or burn a lot of calories in a set amount of time, you should work at higher intensities, or higher heart rates.

What are my target and maximum heart rates?

Your maximum heart rate is estimated to be 220 minus your age. Whether this number is entirely accurate is up for debate. (You can read more about heart rates in one of my earlier columns.)

So considering that your "target" heart rate is based on an estimated maximum, your target heart rate range is also an estimate. So some people may naturally go higher, and some may find it difficult to reach the recommended range, due to individual variation in heart rates. Your target heart rate of 140 seems to be around 80 to 85 percent of your estimated maximum, or in the "vigorous" intensity range. Typically, a calculator gives you a range to work within—a heart rate of, say, 87 to 147 beats per minute, which represents a range of 50 to 85 percent of your maximum heart rate range.

Working at your target heart rate to burn fat

Some people are under the misconception that they burn more fat when working at certain target heart rates. The target fat-burning zone is generally kept at moderate, not higher, heart rates. But the claim that you burn more fat—and, by extrapolation, that you will lose more weight—by working at a lower heart rate is not accurate.

When you work out at a lower heart rate, you burn a higher percentage of fat than you do at higher heart rates. But you are burning fewer total calories. It's not the percentage of fat you burn that matters, but the total amount of calories that you use. So when you work at higher intensities (as seen by higher heart rates), you burn more calories, and therefore more fat.  I explain more about burning fat here.

When should my heart rate be higher or lower?

Generally it's recommended that you warm up for five to 10 minutes before a cardiovascular workout. During this period your heart rate should be on the lower end as you rise from a resting beat to an exercising pace.

After you have warmed up you can vary how high and how long your heart rate stays in different zones. If you are doing interval training, you would alternate the higher and lower heart rates at regular periods. If you are already fit, you might do a two-minute high intensity burst followed by a one-minute recovery at an easier intensity. Or if you are just starting out, you might reverse that and do a one-minute burst followed by three to five minutes of recovery at a lower heart rate.

If you are simply training for endurance, you might aim for a moderate to moderately high zone, say working at 60 to 70 percent of your maximum for an extended period of time.

Toward the end of the workout you should lower the intensity and perform a cool-down period where you work at a lower heart rate for five to 10 minutes. (The less fit you are, the longer you should take to cool down and to warm up.)

The bottom line is that there is no "right" or "wrong" way to work out while considering one's heart rate. It just depends what your training and fitness aims are. A personal training or running coach can give you more specific advice related to your goals.

Find all articles by Martica.

Do you have a fitness or weight-loss question for Martica? Send e-mail to experts@microsoft.com. Please include Ask Martica in the subject line. Each of our experts responds to one question each week and the responses are posted on Mondays on MSN Health. We regret that we cannot provide a personalized response to every submission.

Martica is a Manhattan-based exercise physiologist and nutritionist and an award-winning fitness instructor. She has written for a variety of publications including Self , Health , Prevention , The New York Times and others. Martica is the author of seven books, including her latest, - Cross-Training for Dummies . (Read her full bio.)