The heart is an unusual organ, part muscle, part electrical system, and, oddly enough, part metaphor — we think of our hearts as the origin of emotion and most especially love. Possibly for this reason, many believe their heart health matters above all else. Now, new research presented at the American College of Cardiology's 63rd Annual Scientific Session finds that the simple formula “220 minus age,” which has been used by doctors for decades in exercise stress tests, is flawed. Because this old formula does not reflect the differences between men and women, the researchers have come up with two new formulas to more accurately gauge peak heart performance.
"The standard that's currently in use is somewhat outdated," said Dr. Thomas Allison, cardiologist and director of stress testing at Mayo Clinic. "Every so often, you need to recalibrate what's considered normal."
Changes in Women, Changes in Hearts
Stress tests, which doctors commonly use when diagnosing heart disease, require patients to exercise near top capacity while a nearby technician monitors heart performance. The old formula used in the exercise stress test, often referred to as the treadmill test, stated that peak performance was 220 minus age. Yet, when researchers recently reviewed the test, they noticed serious limitations. The original study, for instance, included very few women, a weakness common among older research. Plus, since the 1970s, changes in average body weight, fitness levels, and attitudes toward exercise — particularly among women, though for both men and women — suggested it was time to reevaluate the old standard.
Other scientists have attempted to update the formula, but in each case the researchers of the current study, led by senior author Allison, were never completely satisfied as too few people had participated in the stress test experiments. So for their study, Allison and his team analyzed data from 25,000 patients who took stress tests at Mayo Clinic between 1993 and 2006. The population included men and women 40 to 89 years of age who had no history of cardiovascular disease. Not only did the new study use a larger sample group than other studies, it also included data from both men and women participants... and that made all the difference in the world! The researchers found significant differences between men and women, and this, they believed, needed to be key when devising a new formula.
"It's logical that an equation developed 40 years ago based on a group that was predominantly men might not be accurate when applied to women today," Allison stated in a press release. In fact, the new research revealed that although everybody's peak heart rate declines with age, the decline is more gradual in women.
As a result, the old formula overestimated the peak heart rate younger women can achieve and underestimated the peak heart rate of older women.
Two New Formulas
Because of the differences between men and women, the researchers changed the old formula into two new formulas, one for each sex. Women between the ages of 40 and 89, should expect their maximum heart rate to be 200 minus 67 percent of their age. For men in that same age range, the formula is 216 minus 93 percent of their age.
The researchers caution that for women under 40, the ratio may be different. Unfortunately, an insufficient number of tests were performed on younger women to provide reliable results. For younger men, the study showed they have a lower resting heart rate and higher peak heart rate than women. The data also showed how men's heart rates rise more dramatically during exercise and return to normal more quickly after stopping.
That said, the two new formulas can help people understand what they need to achieve in their workouts. Although the researchers did not investigate physiological reasons for these differences, they assume hormones, especially testosterone, may play a role. No matter the reason, the takeaway here is simple: It may be time to adjust your exercise routine.