Effects of heavy load carriage during constant-speed, simulated, road marching.

Load carriage is a key element in dismounted military operations. Load carriage requirements in the field regularly exceed 50% of lean body mass (LBM) and have only rarely been studied. Therefore, our purpose was to determine the metabolic and motivational effects of heavy loads (30-70% LBM) during constant-rate "road" marching on a treadmill. Ten healthy male Army officers carried loads of 30%, 50%, and 70% LBM in an all-purpose, lightweight, individual, carrying equipment pack for 30 minutes, at a speed of 6 km/h. Oxygen consumption (VO2), ventilation, heart rate (HR), respiratory exchange ratio, rating of perceived exertion (RPE), and Self-Motivation Inventory scores were recorded at each trial. Significant increases were observed for VO2, ventilation, and HR between the trials. RPE significantly increased for the 70% LBM trial, compared with the 30% and 50% trials. No significant differences were seen in respiratory exchange ratio or Self-Motivation Inventory scores. Increasingly heavy loads carried in a rucksack resulted in increased VO2, RPE, and HR; therefore, increasing the load that a soldier is required to carry may negatively affect road march performance.