By Cemal Ozemek, Ph.D. and Leonard A. Kaminsky, Ph.D., FACSM
|Cemal Ozemek, Ph.D.||Leonard A. Kaminsky, Ph.D., FACSM|
Cardiopulmonary exercise tests (CPX) are readily applied in both performance and clinical settings to assess an individual’s fitness, the risks of underlying cardiac disease, and to generate exercise prescriptions. Numerous studies have fortified the utility of CPX-derived measures for forecasting mortality risk. Examples of such predictors include (but certainly are not limited to) cardiorespiratory fitness (CRF, or maximal oxygen consumption) and maximal heart rate (HRmax) across healthy and diseased populations. Maintaining a high level of CRF with advancing age can delay functional reductions across numerous physiological systems. Although there is consensus that HRmax declines with age, there has been little to no agreement on the rate at which HRmax declines and whether CRF affects its trajectory.
There are uncertainties in the scientific literature with respect to quantifying the rate of HRmax decline with age. This may be due to study design limitations. A number of large cross-sectional studies have performed symptom-limited tests which do not collect expired gases, which would allow for objective determination of maximal or near maximal endpoints. Therefore, an inadequate exercise exertion could result in underestimating the true HRmax for a given age. Such an effect may also bias regression models reported in study results in a way that suggests a steeper decline of HRmax decline with increasing age. The few longitudinal studies that have examined HRmax decline with age have been limited by small sample sizes. To date, there has only been one cross-sectional study (from the Cooper Clinic in 1977) that compared the rate of HRmax decline with age across predicted CRF tertiles.
In an effort to objectively evaluate the effects of CRF on HRmax decline with age, we conducted a retrospective cross-sectional and longitudinal analysis on CPX data from the Ball State University Adult Physical Fitness Program cohort (see the January 2016 issue of MSSE). Data were available from over 6,000 CPX records of 3,647 men and women, tested between the years 1971 and 2014. Only CPXs that were performed on a treadmill by individuals not taking HR altering medications, who achieved a respiratory exchange ratio >1.0, and were free of heart disease were included for analysis. These subject records then were categorized into high, moderate, and low CRF categories relative to age- and sex-matched peers.
Both cross-sectional and longitudinal analyses of our data revealed an inverse relationship between CRF and rate of HRmax decline with age (high fit= roughly -0.6 beats per min [bpm]/year, moderate fit= roughly -0.8 bpm/year, and low fit= roughly -1 bpm/year). In addition to demonstrating support for a preserving effect of CRF on HRmax with age, these findings have particularly meaningful implications for clinical testing facilities. Many CPX facilities generally base an adequate test as one in which subjects can achieve 85 percent of predicted HRmax (220-age). We found, in our study, that the HRmax prediction equations generated for low fit individuals were similar to the widely used 220-age formula. Uniformly applying the 85 percent of 220-age criteria for determining a CPX endpoint in high or moderate fit cases, therefore, may result in those individuals failing to attain an effort close to their peak CRF level. This could reduce the effectiveness of the CPX for detecting cardiac abnormalities (if they exist) and also lead to the generation of an insufficient exercise prescription.
The present study demonstrates that HRmax declines at a faster rate in lower fit individuals. Thereby, these findings underscore the importance of considering an individual’s CRF relative to normative age and sex values (estimated CRF using the Cooper Clinic standards or measured CRF using the recently published CPX registry) when interpreting HRmax. Additionally, the findings suggest another important benefit of fitness, i.e. a slowing of the decline in HRmax with age.
Viewpoints presented on the ACSM Blog reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Cemal Ozemek, Ph.D., received his doctoral degree from the Human Performance Laboratory at Ball State University. He is currently a cardiovascular research fellow at the University of Colorado Anschutz Medical Campus. His research interests focus on studying the effects of sex hormones on cardiac and vascular aging, as well as studying the effects of physical activity and regular exercise on attenuating age-related cardiovascular declines.
Leonard A. Kaminsky, Ph.D., FACSM, completed his doctoral studies in exercise physiology at Southern Illinois University. He is the John and Janice Fisher Distinguished Professor of Wellness at Ball State University, where he formerly directed the Clinical Exercise Physiology Laboratory. Currently, he is the director of the Fisher Institute for Health and Well-being. His research has focused on relationships among physical activity, physical fitness and health. He presently chairs the advisory board for an initiative to establish a national registry of cardiorespiratory fitness.
This commentary presents Drs. Ozemek’s and Kaminsky’s views on the topic of a research article that they and their colleagues had published in the January 2016 issue of Medicine & Science in Sports & Exercise® (MSSE).