Application and performance of heart-rate-based methods to estimate oxygen consumption at different exercise...

Heart rate (HR) is a widespread method to estimate oxygen consumption ( $$ O₂), exercise intensity, volume, and energy expenditure. Still, accuracy depends on lab tests or using indexes like HR_net and HR_index. This study addresses HR indexes' applicability in postmenopausal women (PMW), who constitute over 50% of the aging population and may have unique characteristics (e.g., heart size) affecting HR use.

Fourteen PMW underwent a cycling ramp incremental test to establish the relationships between $$ O2 (in MET) and absolute HR, HR_net, and HR_index. In a second group of ten PMW, population-specific and general equations were tested to predict MET and energy expenditure during six constant work exercises at various intensities. Pulmonary gas exchange and HR were continuously measured using a metabolic cart. Correlations, Bland-Altman analysis, and two-way RM-ANOVA were used to compare estimated and measured values.

Strong linear relationships between the three HR indexes and MET were found in Group 1. In Group 2, population-specific equations showed medium-to-high correlations, precision, and no significant biases when estimating MET and energy expenditure. HR_net and HR_index outperformed absolute HR in accuracy. General HR equations had similar correlations but exhibited larger biases and imprecision. Statistical differences between measured and estimated values were observed at all intensities with general equations.

This investigation confirms the suitability of HR for estimating aerobic metabolism in one of the most significant aging populations. However, it emphasizes the importance of considering individual variability and developing population-specific models when utilizing HR to infer metabolism.