“Optimal” speed–load combinations for military manoeuvres

Abstract Establishing a balance between the physical and mental demands imposed on soldiers and the objectives of the military poses a unique challenge which has been researched for almost a century (J. Roy. Army Med. Corps 40, 41 (1923) 435, 12; Ergonomics 21(5) (1978) 373; Eur. J. Appl. Physiol. 63 (1991) 89; Ergonomics 43(3) (2000) 293). The purpose of this project was to identify “optimal” speed–load combinations which would reduce the physical stress being imposed on the soldiers, while at the same time be effective to meet the demands of military manoeuvres. Thirty male soldiers with a mean age 29.2 (±3.02) yr from a local army base in South Africa participated in an ongoing army contract which investigated the responses of soldiers to 16 varying combinations of speed and load (Metabolic responses of South African soldiers during simulated marching with varying combinations of speed and backpack load, under review). The focus of this paper is to report on the three “optimal” combinations identified in the above contract. The three conditions investigated were: A: speed 3.5 km h −1 −load 50 kg; B: speed 4.5 km h −1 −load 35 kg; C: speed 5.5 km h −1 −load 20 kg. The stature of the soldiers was 1711.5 (±61.6) mm, with a mass of 68.2 (±8.7) kg and percentage body fat of 17.4 (±3.9)%. All subjects wore standardised military uniform including boots and helmets, but excluding rifles. The weight of the battle jacket was kept constant at 11.1 kg for the three conditions, and only the backpacks were adjusted to make up the required loads of 20, 35 and 50 kg. One-way ANOVAs conducted on the responses to the three conditions proposed as “ideal” combinations of varying speeds and adjusted loads revealed no significant differences. It could therefore be concluded that although the speeds ranged from 3.5 to 5.5 km h −1 , and the loads varied from 20 to 50 kg, the selected combination of speed and load illicited similar responses. It is thus contended that the results of this research demonstrate that the interplay between speed of marching and the load of the backpack plays a crucial role in ensuring that similar metabolic and psychophysical demands are retained at a bearable level for the soldiers, while meeting specific military requirements. Relevance to industry Load carrying is an integral aspect of the military and indeed many industries, particularly in developing countries. As the need for speed or load dominates so the other factors need to be adjusted in order to retain an acceptable energy cost required to complete the task.