Quantification of energy expenditure of military loaded runs: what is the performance of laboratory-based equations when applied to the field environment?

Abstract

Introduction: Performance during army loaded runs provides a synthetic indicator of a soldier's capacity to move while carrying loads and thereby remain able to execute a mission. The aim of this study was to estimate and compare the energy expenditure (EE) of army loaded runs, conducted in a field environment using laboratory-based equations and HR index (HR_index).

Methods: 45 Ranger recruits had HR monitored during three loaded runs (10, 15 and 20 km) in full military equipment in the field environment. EE was calculated using reference equations (EE-Eq) and estimates of oxygen consumption based on HR_index (EE-HR_index). Correspondence between EE-Eq and EE-HR_index estimates was evaluated using a two-way analysis of variance, correlation test and Bland-Altman analysis.

Results: EE-Eq relative to time and weight was significantly higher for the 10 km (0.175±0.016) compared with 15 and 20 km (0.163±0.016 and 0.160±0.013 kcal/kg/min, not different). The overall EE-Eq increased significantly with distance (1129±59, 1703±80 and 2250±115 kcal for 10, 15 and 20 km). EE-Eq was not different from and highly correlated with EE-HR_index, with a small and non-significant bias and good precision between methods.

Conclusions: Our study provides the first comprehensive data on HR and EE during long-distance loaded army runs, in full combat equipment, in actual field conditions. Equation-based estimates of EE during these heavy-intensity activities were not significantly different from and highly correlated with HR-based estimates. This corroborates the general applicability of the predictive equations in the field environment. Furthermore, our study suggests that time-resolved HR-based estimates of EE during army runs can be used to evaluate for the effects of context specificity, individual variability and fatigue in movement economy.

Keywords: heart rate index; loaded locomotion; military training; special forces.