Heart rate-based metabolic rate estimation for military-relevant exercises

Introduction Accurate assessment of metabolic rate (Ṁ) is critical for optimizing performance and mitigating risks in military personnel. However, traditional methods like indirect calorimetry are impractical in field settings. This study developed and validated a heart rate (HR)-based algorithm with improved accuracy for estimating Ṁ during military relevant activities. Purpose Construct and validate an algorithm for estimating metabolic rate during standing, walking, and running solely from HR with an adaptable framework that allows for the integration of cardiometabolic fitness parameters to enhance precision when such information is accessible. Methods We compiled a dataset of cardiometabolic data from healthy adults performing steady-state activities (standing, walking, running) for algorithm development. External validation was performed using data from a separate cohort of adults across thirteen studies. The Heart Rate–based Metabolic Estimation Tool (HR-MET) estimates Ṁ based on HR and, optionally, cardiometabolic fitness parameters (HR_max, HR_rest, Ṁ_max, Ṁ_rest). Statistical equivalence between estimated and measured Ṁ was determined if the 90% confidence interval of the mean percent paired difference was within ±10%. Results Using the algorithm development dataset, the HR-MET with all cardiometabolic fitness parameters resulted in a root-mean-square deviation (RMSD) of 0.89 W kg⁻¹ and a concordance correlation coefficient (CCC) of 0.953. Analysis of the external validation dataset found an RMSD of 1.18 W kg⁻¹ and CCC of 0.961. Statistical equivalence was demonstrated between estimated and measured Ṁ in both datasets when using all available cardiometabolic fitness parameters. Conclusion The HR-MET provides a valid and accurate method for estimating metabolic rate during military activities based on HR that can be further optimized with the inclusion of cardiometabolic fitness parameters. This combination of laboratory accuracy and field applicability of the HR-MET can advance readiness, safety, and performance across recreational, occupational, athletic, and military domains.