There are multiple formulae for estimating maximal heart rate (HR) including the most frequently used, 220 minus your age in beats per minute (BPM). These formulae are excellent for estimating the average HR for a population, but all of these estimates have a large standard deviation (SD) because individual maximal HRs vary greatly. In fact, the standard deviation (SD) for maximal HR is ~ +/- 15 BPM, and can be as high as 25 BPM in some studies. And since “normal” is usually defined as the within the 95% confidence limits, which is the mean value +/- 1.96 times the SD, a maximal HR is still normal if it’s 220 – the age +/- 30. It could even be +/- 50 BPM if we use the SD from the study cited below.*
Reproduced from reference below.* The values are means and (SD).
So, there are two reasons why you should care:
#1. Patients are referred to clinicians who are interested in exercise because the patient cannot reach “their maximal HR” during exercise so there must be something wrong. I usually do an exercise stress test to document the HR response and to exclude any exercise-induced conduction abnormalities. I exclude medicines and hypothyroidism, but I usually administer that wonder drug, reassurance, in large doses if the patient is otherwise well. “Their” maximal HR is not their maximal HR.
#2. Patients often have their exercise stress test (EXT) stopped before they have performed their maximal effort because they reached 85% of their predicted maximal HR. This often infuriates athletes undergoing testing because they could have gone longer. It also eliminates the chance of seeing what happens to the patient at their maximal effort. Do they develop the arrhythmia they have been complaining about? Do they develop angina at near maximal effort? Alternatively, the EXT is deemed inadequate because the patient did not achieve 85% of their predicted maximal HR, even though the patient gave his/her maximal effort. EXTs should be maximal effort EXTs and not maximal-estimated-HR EXTs because the estimated maximal HR is often wrong.
The Rules: Know that estimating maximal HR by any age equation has a large SD. Remember that maximal EXTs should be maximal effort EXTs and not guesstimated maximal HR EXTs .
*Laukkanen JA, Mäkikallio TM, Rauramaa R. et. Al. Cardiorespiratory fitness is related to the risk of sudden cardiac death: a population-based follow-up study. J Am Coll Cardiol 2010;56:1476–83. PMID: 20951323