A reader who runs 5Ks posted a question recently which indicated concern that his heart rate during intense exercise was much higher than his age-predicted heart rate. He writes
I’m 65, exhaustion HRmax is 188, HRave for 5k is usually 152-154 and interval HRmax is usually 175-179 depending on how hard I push”
He wondered if he should be concerned about being a “high-beater.”
This prompted the skeptical cardiologist to examine the literature on age-predicted maximal heart rate which led to the shocking discovery that the wrong formula is being utilized by most exercise trainers and hospitals.
First , some background.
The peak heart rate achieved with maximal exertion or HRmax has long been known to decline with aging for reasons that are unclear.
The HR achieved with exercise divided by the HRmax x 100 (percentage HRmax) is widely used in clinical medicine and physiology as a basis for prescribing exercise intensity in cardiac rehab programs, disease prevention programs and fitness clinics.
During stress tests we seek to have patients exercise at least until their heart rate gets to at 85% of HRmax.
The Traditional Formula For HRmax
The formula that is widely used for HRmax is
HRmax = 220-age
It appears to have originated from flawed studies in the early 1970s. These studies included subjects with cardiovascular disease, smokers and patients on cardiac medications.
The Improved HRmax Formula
Tanaka, et al in 2001 performed a meta-analysis of previous data on HRmax along with accumulating data in their own lab. This was the first study to examine healthy, unmedicated, nonsmokers. In addition each subject achieved a verified maximal level of effort as documented by metabolic stress testing.
Their analysis obtained the regression equation (which I term the Tanaka equation)
HRmax = 208-(0.7 x age)
Below is the graph of the laboratory measurements from which the regression equation was obtained.
This graph shows how inaccurate the traditional equation is, especially in older individuals like my reader:
The traditional equation in comparison to the Tanaka equation overestimates HRmaxin young adults, intersects with the present equation at age 40 years and then increasingly underestimates HRmaxwith further increases in age. For example, at age 70 years, the difference between the two equations is ∼10 beats/min. Considering the wide range of individual subject values around the regression line for HRmax(SD ∼10 beats/min), the underestimation of HRmaxcould be >20 beats/min for some older adults.
There are likely lots of perfectly healthy individuals in their sixties and seventies then who have heart rates at maximal exertion that exceed by 10 to 20 beats per minute the HR max predicted by the traditional formula.
This is due to a combination of the inaccuracy of the traditional formula and the wide variation in normal HR max at any given age (standard deviation (SD) of approximately 10 beats/min.)
Thus, my reader at age 65 would have a HRmax predicted by the Tanaka equation as
208-0.7 x 65=162
If we allow for a 10 BPM range of normality above and below 162 BPM we reach 172 BPM which gets close to but doesn’t reach the reader’s 188 BPM.
If you examine the scatterplot of the Tanaka data you can see that several of the points for age 65 reach into the 180s so chances are my reader is still within normal limits
The Bottom Line on HRmax
The widely used traditional formula for predicting HR max is inaccurate.
Athletes, trainers, physicians and hospitals should switch to using the superior Tanaka HR max formula.
Individuals should keep in mind that there is a wide range of HR response to exercise in normals and variations of 10 BPM above and below the predicted response are common and of no concern.
Addendum. The 220-age formula is so heavily etched into my brain that I used 220 instead of 208 when I initially calculated the predicted max HR for my reader. this has been corrected.Thanks to Chris Sivewright for pointing this out.