For a Better Workout, Target Your Heart Rate
Have you ever stopped to wonder, mid-hike or jog or bike ride, exactly how hard you're exercising? I mean, sure, you know how you're feeling: Breathing heavily? Check. Breaking a sweat and having difficulty talking? Check, check. But in order to definitively measure your activity level, consider tracking your heart rate. "It's an extremely useful tool, especially for people just starting out," says Scott Crouter, PhD, an assistant professor of exercise and health sciences at the University of Massachusetts–Boston. "You'll have an actual number to place on how hard you're working, which allows you to see if you're in a range where you're getting moderate activity, or maybe working too hard and need to slow down a little."
What he's talking about is target heart rate training: calculating your maximum heart rate and then using that number to figure out how vigorously you need to exercise to make your heart beat in a "target zone," to ensure a moderate or more intense workout. It can help you gauge your initial fitness level and then set goals and monitor progress in nearly any fitness program, from walking and running to playing tennis or even swimming. "You can use it as kind of a tracking guide," says Crouter, "a mental diary you can record every day that helps hold you accountable, by asking, 'Am I working hard enough? What exactly did I do today, and did I do enough?' "
Why is it important to know how strenuously you're exercising? For starters, upping the intensity of a workout can lead to maximum health and fitness benefits, especially for people with diabetes, says Sheri Colberg, a professor of exercise science at Old Dominion University in Norfolk, Va., and author of The Diabetic Athlete's Handbook. "Doing more intense work is important for long-term blood sugar control," she explains. "It uses more of the carbs stored in the muscles called glycogen, and the more glycogen you use during a workout, the more sensitive to insulin you are afterwards."
For people with diabetes or prediabetes, the American Diabetes Association recommends at least 150 minutes a week (or 30 minutes a day, five days a week) of moderate-intensity aerobic activity. Regular exercise can help prevent or delay type 2 diabetes in people at high risk. The American College of Sports Medicine and the American Heart Association recommend the same exercise formula for healthy adults, or vigorous-intensity aerobic activity for at least 20 minutes, three days a week, combined with a strength-training program twice a week. "So [target heart rate training] can be a time-saving device," says Colberg. "Of course, if you're just starting out, you shouldn't jump right into intense exercise. You may start out walking 30 minutes to an hour each day, but at some point [you may] run out of that much time, so instead of giving exercise up entirely, you can shift focus to monitoring how hard you're working. . . . You can also mix and match moderate and more intense exercise."
To get started, you need to know your maximum heart rate, which is determined by a simple equation: 220 minus your age. Now all you have to do is take your pulse from time to time during a workout and calculate your heart rate per minute (see box, opposite, for instructions). Then aim to stay within your "key target training zone," which is from 60 to 80 percent of your maximum heart rate, along these lines:
From 60 to 70 percent:
From 70 to 80 percent:
Over 80 percent:
So, for example, a 40-year-old woman's maximum heart rate is 180 (220 minus 40). For a moderate workout, she will want to keep her heart rate between 126 and 144 (70 and 80 percent, respectively, of 180).
Training at a medium to high intensity will give you the greatest health and fat-burning benefits from cardiovascular activity. Still, both Crouter and Colberg advise caution and suggest starting at the lower end of your target zone—even 50 to 60 percent of your maximum heart rate. Then you can gradually build up to the point that you're able to exercise comfortably at about 80 percent of your maximum heart rate. Also bear in mind that you don't have to follow the numbers exactly, especially at the start. Some days your body just won't feel as well—or as up to an all-out bike ride or swim—so plan to rely on your general feelings, which are a fairly reliable indicator of when you need to back off a bit. Remember: The worst thing would be to work out too hard, too soon, and then get burned out and quit altogether.
Of course, different experts and organizations have slightly different views on target heart rate zones. While the equation mentioned above is the easiest way to calculate maximum heart rate, some experts have begun to recommend the Karvonen method, which takes resting heart rate into account (measured by taking your pulse for one minute first thing in the morning, before you get out of bed) and is widely considered to be more accurate. "[It] allows you to take into account that people have varying resting heart rates," says Colberg. "Particularly with diabetes, you can have an elevated resting heart rate—let's say if you have autonomic neuropathy or if you're simply really out of shape. The more in shape you are, the lower your resting heart rate gets, so this allows you to adjust the range as you get more fit, and keeps the whole calculation individualized." The easiest way to use this more complex equation is with quick-and-easy online calculators; you can find one by entering the term "Karvonen calculator" in a search engine.
While heart rate training can be an excellent tool, there are some dangers to be aware of. "Heart rate training, on a general level, works pretty well, but the big thing we're always concerned about . . . is what types of medications people are on," says Crouter, explaining that numerous drugs can affect heart rate, like beta-blockers, which lower both resting and maximum heart rate. In addition, people with pacemakers, irregular heartbeats, or any type of cardiovascular problem are particularly vulnerable to heart rate fluctuations, and many other factors can influence your pulse, including stress, illness, overtraining, and fatigue. You should always check with a physician before upping the intensity of any workout routine with heart rate training.
Does all this seem a bit much? When in doubt, go back to how you're feeling with the "talk test." The test can be quite useful in figuring out how hard you're working, especially when combined with tracking heart rate: During your workout, simply try to maintain a pace where it's possible to chitchat without too much trouble, and you're most likely getting a moderate workout; if you can sing along with your iPod, it's probably not challenging enough; and if you're having serious trouble breathing, it's without a doubt too much, too soon. Listen to your body, and you can't go wrong.