Metabolic Costs of Walking with Weighted Vests

Abstract

Introduction: The US Army Load Carriage Decision Aid (LCDA) metabolic model is used by militaries across the globe and is intended to predict physiological responses, specifically metabolic costs, in a wide range of dismounted warfighter operations. However, the LCDA has yet to be adapted for vest-borne load carriage, which is commonplace in tactical populations, and differs in energetic costs to backpacking and other forms of load carriage.

Purpose: Develop and validate a metabolic model term that accurately estimates the effect of weighted vest loads on standing and walking metabolic rate for military mission-planning and general applications.

Methods: Twenty healthy, physically active military-age adults (4 women, 16 men; age, 26 ± 8 years old; height, 1.74 ± 0.09 m; body mass, 81 ± 16 kg) walked for 6-21 min with four levels of weighted vest loading (0-66% body mass) at up to eleven treadmill speeds (0.45-1.97 m·s-1). Using indirect calorimetry measurements, we derived a new model term for estimating metabolic rate when carrying vest-borne loads. Model estimates were evaluated internally by k-fold cross-validation and externally against twelve reference datasets (264 total participants). We tested if the 90% confidence interval of the mean paired difference was within equivalence limits equal to 10% of the measured walking metabolic rate. Estimation accuracy, precision, and level of agreement were also evaluated by the bias, standard deviation of paired differences, and concordance correlation coefficient (CCC) respectively.

Results: Metabolic rate estimates using the new weighted vest term were statistically equivalent (p < 0.01) to measured values in the current study (Bias, -0.01 ± 0.54 W·kg-1; CCC, 0.973) as well as from the twelve reference datasets (Bias, -0.16 ± 0.59 W·kg-1; CCC, 0.963).

Conclusions: The updated LCDA metabolic model calculates accurate predictions of metabolic rate when carrying heavy backpack and vest-borne loads. Tactical populations and recreational athletes that train with weighted vests can confidently use the simplified LCDA metabolic calculator provided as Supplemental Digital Content to estimate metabolic rates for work/rest guidance, training periodization, and nutritional interventions.