The Impact of Load and Grade on Energy Expenditure During Load Carriage, Part II: Field Study

Abstract

The metabolic costs of load carriage were measured for 8 volunteers on uphill, level and downhill grades at Yakima Training Center (YTC). Volunteers carried loads of 0, 13.6 or 27.2 kg as they walked on grades of 0% (level), +/- 14%, +/- 8.6% and approx. 12% at 3 mph. Mean values for oxygen consumption (VO2) during load carriage indicate costs increased with increasing load and uphill grade, and decreased with negative grades. A mathematical model, using a terrain factor of 1.1 for sites with gravel, was used to calculate load carriage costs. Those values were compared to field data. Results for the negative data showed no significant difference between the model and downhill measurements. For the +8.6% grade there was a significant difference between the measured and model calculated values, which underestimated the measured costs. Results obtained under field conditions were also compared to results obtained under laboratory conditions on treadmill grades of 0%, +/- 4%, +/- 8% and approx. 12%. When the field data were compared to laboratory values, the field data were also higher than the laboratory data. It is possible that the difference between observed and model calculated values reflects a difference between laboratory and field conditions.