Soldier load carriage: historical, physiological, biomechanical, and medical aspects.

This study reviews historical and biomedical aspects of soldier load carriage. Before the 18th century, foot soldiers seldom carried more than 15 kg while on the march, but loads have progressively risen since then. This load increase is presumably due to the weight of weapons and equipment that incorporate new technologies to increase protection, firepower, communications, and mobility. Research shows that locating the load center of mass as close as possible to the body center of mass results in the lowest energy cost and tends to keep the body in an upright position similar to unloaded walking. Loads carried on other parts of the body result in higher energy expenditures: each kilogram added to the foot increases energy expenditure 7% to 10%; each kilogram added to the thigh increases energy expenditure 4%. Hip belts on rucksacks should be used whenever possible as they reduce pressure on the shoulders and increase comfort. Low or mid-back load placement might be preferable on uneven terrain but high load placement may be best for even terrain. In some tactical situations, combat load carts can be used, and these can considerably reduce energy expenditure and improve performance. Physical training that includes aerobic exercise, resistance training targeted at specific muscle groups, and regular road marching can considerably improve road marching speed and efficiency. The energy cost of walking with backpack loads increases progressively with increases in weight carried, body mass, walking speed, or grade; type of terrain also influences energy cost. Predictive equations have been developed, but these may not be accurate for prolonged load carriage. Common injuries associated with prolonged load carriage include foot blisters, stress fractures, back strains, metatarsalgia, rucksack palsy, and knee pain. Load carriage can be facilitated by lightening loads, improving load distribution, optimizing load-carriage equipment, and taking preventive action to reduce the incidence of injury.