The effects of cardiorespiratory fitness on the decline of maximal heart rate with age

Background: Previous investigations have commonly generated HRmax prediction equations by linearly regressing HRmax with age. Little is known regarding the impact of objectively measured cardiorespiratory fitness (CRF) and gender on the rate of decline in HRmax with age and whether HRmax declines linearly. Lastly, most HRmax prediction equations only include age, therefore it is not known if adding additional subject characteristics will improve the prediction of HR max.;Methods: Cardiopulmonary test (CPET) records were drawn from the Adult Physical Fitness Program (APFP) database, which consisted of 4984 test records. CPETs were included if the individual performed a CPET on a treadmill and achieved a respiratory exchange ratio (RER) [special characters omitted]1.0. The first valid test record from each individual was used in the cross-sectional (CS) examination (1161 men, 1070 women). To be included in the longitudinal analyses (LA) (282 men, 172 women), participants had to have completed [special characters omitted]2 CPETs with [special characters omitted]1 year between testing dates. To test the effect of CRF on the decline in HR max with age, subjects were categorized into respective CRF categories (high, moderate, and low) based on the BSU CRF normative classifications. Linear and quadratic regression equations were developed between age and HR max. A multiple regression analysis was performed using age, gender, weight, body mass index, body fat percent, fat free mass, resting HR, resting systolic blood pressure (SBP), physical activity, smoking status and maximal oxygen consumption (VO2max).;Results: High fit individuals had a slower rate (beats per min [bpm] per year) of decline in HRmax than moderate and low fit subjects for both CS (-0.61, -0.79, -0.90, respectively) and LA (-0.65, -0.83, -1.07, respectively). Men in the low fit group in the cross-sectional, and moderate fit men in the longitudinal analysis, had a faster rate of decline in HR max with age compared to women in the CS analysis. For the whole cohort, linear and quadratic equations did not differ, however there was a greater divergence between equations at older ages (60+ years) in the low fit group. In the CS analysis, age, resting HR, smoking status, gender, and weight accounted for 44% of the variance in HRmax. When including VO2max in the model, age, physical activity, resting SBP, body fat percent, and BMI accounted for 48% of the variance in HRmax, and reduced the standard error of the estimate from 11.4 to 10.7 bpm. In the LA only age and resting HR were included in the model, which was improved by including VO2max .;Conclusions: The maintenance of a high CRF can slow the rate of decline in HRmax over time. Additionally, the rapid decline in HR max in the older, low fit group may be of clinical importance since abnormally low HRmax values (<85% of age predicted HRmax ) are associated with increased risk of mortality. Attention should be given to monitoring alterations to the rates of decline in HRmax with age, relative to CRF.