Predicting Individualized Cardiovascular Responses To Loaded Military Exercise

Abstract

Periodized endurance training requires exercise-specific knowledge of the cardiovascular demands of training to optimize long-term performance improvements. Tactical strength and conditioning communities lack resources for forecasting heart rate responses to common endurance exercises performed by dismounted warfighters such as military load carriage. PURPOSE: Develop an individualized model for predicting steady-state heart rate responses to walking with military backpack loads. METHODS: Thirty volunteers (3 women, 27 men; age, 25 ± 7 years old; height, 174 ± 7 cm; body mass, 77 ± 15 kg) carried backpacks loaded up to 66% body mass on a treadmill at walking speeds from 0.45 to 1.97 m·s-1. Heart rate responses were measured continuously using a chest-worn physiological status monitor (Equivital EQ02+ LifeMonitor (EQ02+); Equivital; Cambridge, UK) and averaged over the final minute of each trial. A new model was fit using a nonlinear mixed effects modeling approach that predicts a heart rate response to given walking speed and backpack load that is scaled to each individual’s resting and maximal heart rate. Model predictions were deemed statistically equivalent if the 90% confidence interval around the mean error was within equivalence limits set to ± 5% of the mean measured heart rate. RESULTS: The mean heart rate measured across volunteers and trials was 111.7 ± 25.1 bpm, setting the equivalence limit to ± 5.6 bpm. Model predictions were statistically equivalent to the measured heart rate data (90% Confidence Interval [-1.8, 2.4 bpm]). CONCLUSION: The model developed herein allows users to determine the pace and load to elicit a target heart rate for optimal training. Heart rate predictions can be used for designing individualized training intensity zones and benchmarks for ruck marching and hiking programs. Combining these cardiovascular estimates with existing metabolic and thermoregulatory models allows for more comprehensive planning of military exercises. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.