Female Energy Expenditure during Load Carriage in Thermal Environments

Existing biomedical models that predict the rate of metabolic energy expenditure (M˙) were developed almost exclusively with male participants in temperate environmental conditions, necessitating empirical data to modify existing or generate stand-alone model terms for thermally stressful conditions in females. Purpose – To cross-validate the Load Carriage Decision Aid (LCDA) in healthy, military-aged, load carriage–naïve females in thermal environments. Methods – During seven experimental trials, varying from cool to hot environments (10°C, 20% relative humidity (RH); 22°C, 20% RH; 31°C, 20% RH; 40°C, 20% RH; 45°C, 20% RH; 31°C, 60% RH; 40°C, 60% RH), 27 females aged 18–35 yr walked at increasing speeds with and without load carriage. Paired mean differences between measured (indirect calorimetry) and estimated (LCDA) M˙ were evaluated using bias, concordance correlation coefficient (CCC), and statistical equivalency (±10%) tests. Results – LCDA estimates of M˙ were excellent in 22°C, 20% RH (Bias ± SD, −0.01 ± 0.33 W·kg⁻¹; CCC, 0.992) with acceptable precision in other dry (20% RH) conditions: 10°C (−0.23 ± 0.39 W·kg⁻¹; 0.969), 31°C (−0.13 ± 0.31W·kg⁻¹; 0.989), 40°C (−0.24 ± 0.34 W·kg⁻¹; 0.972), and 45°C (−0.25 ± 0.35 W·kg⁻¹; 0.971). In humid conditions (60% RH), the LCDA performed well in 31°C (−0.15 ± 0.31W·kg⁻¹; 0.983) but was unacceptable in 40°C (−0.33 ± 0.30 W·kg⁻¹; 0.959). Statistical equivalence was detected for each environment except for 40°C, 60% RH (90% confidence interval, −10.1% to −6.7%). Conclusions – In females, the LCDA can confidently be used to estimate walking M˙ with and without load across a wide range of environments. Higher than expected energy costs should be expected in hot, humid conditions.