By Janet Weller, RN
Maximum Heart Rate Formula: Missing the Mark?
Recent studies point to shortcomings in the common calculation method, especially for young and older adults.
hile for 30 years the fitness industry has relied on the formula 220 minus age (plus or minus 10 percent) to determine maximum heart rate, most trainers have seen clients whose numbers simply did not match the formula. Devised by William L. Haskell, MD, currently a professor of medicine at Stanford University, Palo Alto, California, the formula was never intended as an absolute guideline. According to Hirofumi Tanaka, PhD, researcher at The University of Colorado at Boulder, there is good reason for this. In his studies on aging and cardiovascular fitness, Tanaka found the traditional formula underestimates maximal heart rate for older adults and overestimates it for younger adults. According to Tanaka, the original research did not take into account an older population. In research published in the Journal of the American College of Cardiology, Tanaka, Kevin Monahan, MS, and Douglas Seals, PhD, propose using 208 minus 70 percent of age as the new formula.
Crunching the Numbers Tanaka's research includes an analysis of age-predicted maximal heart rate using published literature, combined with lab testing of the new formula. They did a meta-analysis of 351 studies and tested 514 subjects. The findings show the original formula overestimates maximal heart rate in young adults; the formulas intersect at age 40, and then the original formula increasingly underestimates maximal heart rate in older adults. For example, a 70-year-old woman would have an agepredicted maximal heart rate of 150 using 220 minus age; using the new formula it would be 159. A 20-year-old would have a maximal heart rate of 200 using the old formula, or 194 using the new one. Tanaka does state, "Maximal heart rate has a standard deviation of about 10 beats per minute. So even if you use this new equation, it is not a perfect prediction." Though the new formula has received major media attention, American Council on Exercise (ACE), American College of Sports Medicine (ACSM) and Aerobics and Fitness Association of America, among other fitness agencies, have not yet changed their guidelines for the maximal heart rate formula. According to Barry Franklin, PhD, director of Cardiac Rehabilitation and Exercise Laboratories at William Beaumont Hospital in Royal Oak, Michigan, a variety of new formulas have come up over the years, and it takes time for each new formula to be evaluated. However, he notes that the guidelines are constantly being reevaluated and ACSM guidelines may eventually make reference to the new formula. In the meantime, all heart rate formulas, including the Karvonen formula (training heart rate equals maximum heart rate minus resting heart rate, times desired intensity [50 to 90 percent], plus resting heart rate) and those for submaximal tests, use 220 minus age for maximal heart rate. What are we as trainers to do?
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RATING OF PERCEIVED EXERTION SCALES (BORG)
Category Scale 6 No exertion at all 7 Extremely light 89 Very light 10 11 Light 12 13 Somewhat hard 14 15 Hard 16 17 Very hard 18 19 Extremely hard 20 Maximal exertion Category-Ratio Scale 0 Nothing at all 0.5 Extremely weak (just noticeable) 1 Very weak 2 Weak (light) 3 Moderate 45 Strong (heavy) 67 Very strong 8910 Extremely strong (almost max)
of being at the proper exercise intensity, and it will make exercise a bit safer." Walter Nolan, personal trainer and vice president of VIP Fitness, Fort Lee, New Jersey, is not surprised to hear of the inaccuracy of the original maximal heart rate formula. In his work as a certified New York State soccer and track coach he has often noticed that cyclists frequently train well above their age-predicted maximum heart rate. He uses perceived exertion with his clients: "What I do [with more athletic, fit clients], is during their exercise session, if I've picked a number toward the top of the zone, I will use the perceived exertion scale and say: `Try to mimic this when you're on your own.'"
HOW THE FORMULAS COMPARE
Formula Traditional Formula Karvonen Formula New Formula Example 220 - 68 152 - 60 x 90% + 60 208 - 70% of 68 Outcome 152 142.8 160.4
Perceived Exertion the Answer? Richard Stein, MD, chief of cardiology, Brooklyn Hospital Center in New York, and Franklin both promote maximal stress tests: "It is always best to have the maximal heart rate actually measured and to base the prescribed exercise intensity on that heart rate," Franklin states. However, healthy young adults with no risk factors are unlikely to spend up to $275 for such tests, and cardiologists may not test those with heart disease to their maximal level of exertion. Maximal stress tests have their limitations as well; exercisers may stop because of muscular discomfort and not reach their maximal heart rate. Stein, Franklin and Tanaka all agree that perceived exertion is the next best thing. "I'd say in 90 percent of contemporary exercise prescriptions we've given up on heart rate determined by exercise levels." Stein says. "Most of us
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who do this for a living have defaulted to what is called rating of perceived exertion (RPE)." He suggests using the Borg scale, either the original scale from six to 20, or the modified scale of zero to 10. Jeffrey Potteiger, PhD, director of the Health and Human Performance Laboratory at Virginia Commonwealth University, Richmond, Virginia, agrees that perceived exertion can be an effective tool. According to Potteiger, studies have compared exercise intensity using heart rate and RPE, or a combination of both. "The people using heart rate and perceived exertion in combination were better able to gauge their exercise intensity while walking/running on a treadmill. We are better off telling people to use heart rate as well as the RPE. Exercise is a physiological and psychological response. If you use both heart rate and RPE together you have a better chance
Teaching Perceived Exertion Stein and Potteiger both caution that perceived exertion has a learning curve. Trainers can best help their clients by taking them through the process. Mary Yoke, MA, exercise physiologist, personal trainer and author of A Guide to Personal Training, agrees that a skilled personal trainer can help clients find their optimal exercise zone. "If you work with a client long enough you can use perceived exertion. Yoke uses the following method to develop a perceived exertion scale on a client-byclient basis: I "I combine the talk test with a heart rate monitor," she explains. "This is a good way to teach exertion levels to my clients, especially those who are new to exercise." I Ask clients to recite a long passage they have memorized--a poem, song or even the pledge of allegiance-- while working at different intensities. I Point out heart rates at different stages and ask clients to give a number for their perceived exertion at different levels. For example, if they are talking easily, they may rate their exertion as a six, but as they get close to breathless, they may rate the intensity an eight or even nine. I The numbers, plus the readout on the heart rate monitor, give tangible,
visible feedback to help clients learn to match their effort level with what they are feeling. Personal Trainer Paul Robbins of CardiO2Tech, Scottsdale, Arizona, describes his method for using perceived exertion to find training zones for his clients: "I give a client one zone to start with (65 percent of max using 220 minus age) to build a base." He then gradually adds intervals to increase the intensity to 80 to 85 percent of maximal heart rate (using 220 minus age). At the beginning the intervals may be just 15 to 20 seconds; depending on the program, clients will build up to three minutes. This may take a few weeks, or months, if they are "unfit." He uses this information to determine the submaximal zone for his clients. He believes clients learn what RPE is by using their own bodies as indicators.
"The talk test does help in this case," Robbins said. He also looks at how long they can train at a steady heart rate. "If a client comes to me and says he does a group exercise class hard for 40 minutes and his heart rate is 150 the whole time, I know that is close to anaerobic threshold, and I will use that as a starting point." The take-home message seems to be that trainers need to educate clients on how to "listen" to their bodies. While people like the sure feel of numbers, both formulas have at least a 10-percent margin of error. "We are all on a bellshaped curve," Potteiger says. "So many factors influence heart rate: caffeine, stress, lack of sleep, etc. We want to measure intensity to get a training effect and to make it safe, but it's not a hard and fast rule." Yoke agrees, stating that heart rate formulas don't match a quarter of the
population. She bases this statement on personal experience, taking into account the standard deviations for the formulas. She also notes that the numbers aren't that different no matter which formula you use. Potteiger says he thinks that trainers can certainly use the new formula, but he suggests using it in conjunction with RPE. It is important for trainers to stay current on the latest research and be aware that new formulas and theories will always crop up, often confusing clients about what is right and wrong. As Yoke says: "A good trainer needs skills and information. These formulas don't fit everyone." When in doubt, listening to the body's "voice" will usually clarify the confusion in the mind. Janet Weller, RN, is an IDEA Master Personal Trainer and freelance writer. You may contact her at email@example.com.
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