Comparison of 2 Methods for Measuring Chronotropic Response to Exercise: Heart Rate–Work Rate Slope Versus Percent Change in Heart Rate–Work Rate Slope—A Cross-Sectional Study

Purpose: Chronotropic response to exercise (CRE) is an indicator of cardiovascular health and is evaluated using different methodologies. The purpose of this cross-sectional investigation was to compare 2 methods for measuring CRE: heart rate (HR)–work rate slope versus percent change in HR–work rate slope. Methods: Thirty-three participants met the inclusion criteria. Participants completed a two-stage graded exercise protocol. Heart rate and work rate data were recorded at rest (0 watts), the final minute of stage 1, and the final minute of stage 2. Heart rate–work rate slope was defined as the slope of HR increase relative to work rate increase. Percent change in HR–work rate slope was calculated as the percent change in HR–work rate slope between stage 1 and stage 2. Results: Spearman correlation coefficient indicated a significant, but relatively low, correlation between the 2 measurements (r s = 0.388, P = .01). The 95% limits of agreement ( z -scores) between the 2 measurements were −2.29 to 2.29, suggesting considerable disagreement. Conclusions: The findings of this study indicated that HR–work rate slope and percent change in HR–work rate slope were not comparable. The low correlation and lack of agreement between the 2 methods could be explained by the possible measurement of different constructs (cardiorespiratory fitness vs coronary artery disease risk). Because of considerable disagreement, clinicians should not make decisions related to patient care using the 2 methodologies interchangeably. The findings of this investigation support the perspective that a standardized procedure for measuring CRE is warranted.