Q. I’m confused about target heart rates. I’m 48 and so am supposed to exercise at a level that keeps me within a heart rate range of 103-137 beats per minute. A heart rate of 146 bpm is said to be 85 percent of my maximum heart rate and a trainer at my gym told me never to get this high. I’m in so-so shape and am trying to lose weight and get more fit. When I use an elliptical machine or run on the treadmill, my heart rate easily reaches 140-150 bpm—but I feel good when it does. I don’t push too hard or experience chest pain. Am I harming myself if I creep into the 85 percent-and-above range?
A. To understand the implications of working at high heart rates, you need to know why hearts may be monitored during exercise, why specific heart rates ranges are recommended and whether the level you are working at will help you reach your fitness goal.
Exercise Works Like A Drug
The whole point of exercising for your health is, among other things, to make your heart stronger. Exercise acts like a drug: You give your body a dose of fitness stress, and it responds by strengthening your heart. Since an overload of too much stress is assumed to be dangerous, researchers have tried to pinpoint exactly how much of the fitness drug a body should get.
Doses of exercise are quantified in different ways, including number of days per week, number of minutes per session, and number of calories burned per session. How hard the exercise is plays a role, too.
As it turns out, the amount of exercise you need depends on your goal.
Exercise Speeds Up Your Heart
The harder you exercise, the faster your heart pumps. Climbing takes more effort and so will produce a higher heart rate than walking on flat roads at the same pace. Running fast is tougher and will produce a higher heart rate than jogging at a moderate pace. As you get fitter, of course, and as your heart gets stronger, harder bouts of exercise become easier, so your heart rate may not be as high doing the same work once you have trained to do it. But in each instance, whether you’re a beginner or a highly trained athlete, your heart rate is representative of the effort you are making—or the exercise intensity at which you are working.
Your intensity is usually expressed in two ways—either as a percentage of your maximum heart rate, or as a percentage of your maximum cardiac output (max VO2, the amount of blood pumped out with each heartbeat).
How Hard Should You Work?
Any movement—even at a very low-effort level such as gardening—is better than being a couch potato. But research has shown that for optimal health improvements—i.e., lowering your risks of disease and death—it’s best to work at an intensity that hovers around at least 60 percent of your maximum effort level.
But this dose will change according to your goal. If you are trying to do more than simply lower your risk of heart disease, and are hoping to become stronger and improve your stamina, higher intensities are more effective. If this is your aim, general recommendations are to challenge yourself to work at levels that represent from 60 percent to about 85 percent of your maximum effort level.
(No one really knows what the effects of working at your maximum possible capacity is since it’s pretty hard to do—talk about a tough workout! —and keep up. Sprinters training for the Olympics and running at all-out speeds are probably close. The presumption is that if you work at 100 percent, your heart is at its max and will give out at that point.)
Off The Charts
For regular folks just trying to get fit, lose weight or train for a marathon, working within the 60 percent to 85 percent ranges is what’s recommended. The target-heart rate formula estimates your ideal heart rate ranges with a calculation that assumes what your maximum heart rate is.
Research in the 1970s showed that maximum heart rates decline with age, irrespective of fitness level or gender. A formula was developed to predict it: 220 minus your age = your maximum heart rate. As with any general estimate meant to apply to a large number of people, there is lots of individual variation. According to the American College of Sports Medicine (ACSM), the standard deviation or amount that this prediction may be off is about 10 to 12 beats per minute in either direction. So that means that a 50–year-old with an estimated maximum heart rate of 170 may actually have a maximum heart rate that’s lower, say 158, or higher, say 182.
You can see that this variation then could affect what the “target” range for a workout would be.
Formulas Aren’t Foolproof
Here’s the glitch. The old formula: “220 minus age” was developed based on less than 10 studies where the subjects were mostly younger than 55 years old. What this means is that the formula may not apply to all ages equally. Researchers at the University in Colorado in Boulder headed up by Dr. Hirofumi Tanaka (now a professor at the University of Texas at Austin) reviewed 351 newer studies and also conducted lab-based experiments on subjects that ranged from 18 to 81 years old and came up with a revised formula that was published in the Journal of the American College of Cardiology in 2001:
These researchers found that the traditional formula overestimated max heart rates for younger people, and underestimated heart rates for older people. “The Tanaka formula is based on a large number of studies and, especially over 60 years of age, probably is more accurate than 220-minus-age formula,” says Dr. William Haskell, a professor at Stanford University School of Medicine, in Stanford, Calif., who developed the original formula. “However, at age 40 years the two formulas give the same value, and between 30 and 50 years the numbers are quite similar.”
Of course, the newer equation is still an estimate and you may still find yourself climbing out of the range. Also, you may still see the old formula used on gym charts. In fact, it’s even still used on the American Heart Association Web site, albeit with a caveat: “The figures above are averages, so use them as general guidelines.” Haskell explains, “While the Tanaka formula is more accurate, it is very difficult to remember and calculate while you are exercising. Thus for most practical purposes the 220-minus-age is still being used.”
How High is Too High?
Your best bet is to stay close to the recommended guidelines and use your own perception of your efforts as a gauge as well. If you feel comfortable working out at higher heart rates, you’re probably fit enough to do so.
To meet your goal of getting fitter, working harder makes sense—as long as you do not show signs of overexertion such as dizziness, nausea or pain. You also burn more calories from working at higher intensities. But you can work towards weight loss working out at low, moderate and high intensities—it just depends on how long you exercise in each case. So if you want to burn 500 calories, it might take about two hours walking, but only one hour running. Be aware that some trainers encourage people to work at lower intensities. For an unfit person this makes sense as they are less likely to want to work hard and more likely to get injured if they do. But trainers who recommend this sometimes explain that you burn more fat by keeping your heart rate lower, or in an “aerobic” zone as opposed to higher “anaerobic” zone. This is a misinterpretation of how the body uses energy.
Bottom line: Vary your intensities, work as hard as you comfortably can, and—most importantly—stick to your cardio workouts for the rest of your life. You’ll get fit, lose fat and help keep it off.
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