Editor's Note: Commentary based on Sydó M. Abdelmoneim SS, Mulvagh SL, Merkely B, Gulati M. Relationship between exercise heart rate and age in men vs. women. Mayo Clin Proc 2014;89:1664-72.

Exercise stress testing has been available for over six decades and is one of the most utilized tests in cardiology. Maximal heart rate is one of the most commonly used variables in cardiology and exercise physiology. It is well-established that heart rate decreases linearly with age. However, there is controversy over the traditional formula of 220 – age in regards to accuracy of predicting maximal heart rate. The basis for maximal heart rate dates back to 1971 when Fox et al. estimated the age-predicted equation of 220 – age. This was determined based on 10 studies with the highest age <65 years old and the majority of subjects <55 years old. The studies varied in their inclusion of those with cardiovascular diseases which were not well-defined. Additionally, there was no exclusion based on beta-blocker use.¹

In this peer-reviewed paper, the goals of Sydó et al. are two-fold: identify the comorbidities that influence peak heart rate and determine the relationship between exercise heart rate and sex.²

The authors retrospectively examined 37,010 patients between the ages of 40 and 89 who underwent non-imaging treadmill stress tests between 1993 and 2010. Patients with known cardiovascular disease, those on rate or rhythm-modifying therapy, those younger than 40 years old, those for whom the test was stopped early due to positive findings, and those with multiple studies were excluded. Data on comorbidities including hypertension, diabetes mellitus, obesity, current smoking, and those with unfit functional aerobic capacity (FAC) <80% were extracted. They examined the relationship between resting heart rate, heart rate reserve, and heart rate recovery.

For men, the peak heart rate regression lines closely matched the traditional 220 – age formula, specifically 221 – 0.95 x age. For women, the regression lines were significantly different, approximately 210 – 0.79 x age. Resting heart rate was significantly higher for women than men, and the heart rate reserve was lower in women than men. The difference in peak heart rate was significantly different between the ages of 40 and 59, with men having higher peak heart rates. However, by the age of 60, the curves crossed and women tended to have higher heart rate than men without being statistically significant. Heart rate recovery was only significantly different between the ages of 50 and 59.

The traditional formula for assessment of maximal heart rate, 220 – age, is applicable to the male population; however, it overestimates peak heart rate in younger women (ages 40-50 years old) and underestimates peak heart rate in older women (ages 50-90). Thus, a different formula should be used to predict maximal heart rate in women.

There are several advantages to this study. It represents the largest clinical cohort analyzed for peak heart rate between men and women, provides data on resting heart rate, heart rate reserve, and heart rate recovery. They illustrate the impact of particular comorbidities on maximal heart rate. Limitations include the uniform study population with 90% of enrolled participants being Caucasian. Secondly, younger patients ages 20-39 were excluded which upon sub-group analysis deviated from the formula. There were few subjects above the age of 80, primarily related to musculoskeletal limitations.²

This is not the first study to challenge the traditional formula.^3-9 A meta-analysis involving 18,712 subjects found a different, single regression formula to predict peak heart rate for both men and women. Regression lines were similar between men and women, allowing them to derive a common formula of 208 – 0.7 x age. This was cross-validated in a separate study of healthy, non-medicated, and nonsmoking individuals. This study supports the proposal that the traditional formula may be overestimating maximal heart rate in young adults and underestimating maximal heart rate in older adults.⁴ A prospective cohort study of 5,437 asymptomatic, healthy women found that the regression equation that best predicted maximal heart rate was 206 – 0.88 x age, again suggesting that the traditional formula overestimates maximal heart rate.³

The American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for exercise testing and training acknowledge the limitation with the traditional formula. The guidelines reinforce that a high degree of variability exists among subjects of identical age (±12 beats per minute) and that the 85% of age-predicted maximal heart rate should not be used in isolation as a termination criterion.^5,6 Percentage of maximal heart rate achieved is not listed under absolute or relative indications for termination of stress testing. It is, however, routinely used to assess the adequacy of exercise testing with a target of 85% predicted maximal heart rate.

There are several clinical implications of using an inaccurate maximal predicated heart rate. Particularly, for those of whom the heart rate maximum formula underestimates true maximum heart rate, exercise testing may be terminated prematurely when reaching 85% of maximum predicted heart rate. Thus, one could fail to obtain diagnostic information, raising the false negative rate. Furthermore, aerobic exercise prescriptions would be based on maximum heart rate targets that are lower than true maximum heart rate. This could translate to an exercise prescription below optimal intensity. Whether or not this would have clinical consequence to long-term health benefits, is unclear. Lastly, the traditional equation may be underestimating aerobic fitness levels.^2,4

Ideally, there should be additional longitudinal studies to address heart rate regression with age. Until we have a better grasp on true maximal predicted heart rate, particularly for women, it is important to use other markers such as signs or symptoms ischemia to guide duration of testing and exercise prescriptions.

References

1. Fox S, Naughton J, Haskell W. Physical activity and the prevention of coronary artery disease. Ann Clin Res 1971;3:404-32.
2. Sydó N, Abdelmoneim S, Mulvagh S, Merkely, B, Gulati M, Allison T. Relationship between exercise heart rate and age in men and women. Mayo Clinic Proceedings 2014;89:1664-72.
3. Gulati M, Shaw L, Thisted R, Black H, Merz C, Arnsdorf M. Heart rate response to exercise stress testing in asymptomatic women: The St. James women take heart project. Circulation 2010;122:130-7.
4. Tanaka H, Monahan K, Seals D. Age-predicted maximal heart rate revisited. J Am Coll Cardiol 2001;31:153-6.
5. Fletcher G, Ades P, Kligfield P, et al. Exercise standards for testing and training: A scientific statement from the American Heart Association. Circulation 2013;128:873-934.
6. Sheffield L, Maloof J, Sawyer J, Roitman D. Maximal heart rate and treadmill performance of healthy women in relation to age. Circulation 1978;57:79-84.

Keywords: Adrenergic beta-Antagonists, Cardiovascular Diseases, Sports, Cohort Studies, Comorbidity, Diabetes Mellitus, Exercise, Exercise Test, Hand Strength, Heart Rate, Hypertension, Longitudinal Studies, Obesity, Prospective Studies, Smoking

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