Physical Agility
Energy costs due to loads are commonly reported in terms of kilojoule (kJ) per unit of time or oxygen uptake. A number of studies have been completed that allows a reasonably accurate prediction of the energy cost of multiple activities in different environments. Comparing this with an individual’s maximum aerobic capacity allows some measure of sustainment capacity. Task intensity measured against individual capacity provides a good way of defining how weight can impact performance e.g. the more intense the activity the less time it can be sustained, and vice versa.
The graph on the right shows walking speed energy use at different external loads, from 20kg to 50kg. If the reference is a 20Kg external load, 3km/hr on a flat firm surface, increasing the weight to 30kg results in an energy requirement increase of 12% but if the weight is increased to 50kg, it goes up by 50%. This can be translated into rules of thumb for weights and speeds, characterised by the table below.
Duration task, terrain, climate, altitude and individual fitness will all have an influence but as one might expect, more weight makes every task harder and/or slower. Recent studies (Silk 2010) demonstrated an average decrease in soldier mobility performance of 1,5% for every 1kg carried. Another study (Basaan 2005) looked at the time to complete an obstacle course and found that for every 1kg increase in external load (between 15 and 42kg) the time to complete increased by just under 8 seconds.
Terrain accessibility is also a significant factor for overburdened personnel, the images above show soldiers having trouble crossing even small gaps unaided, speed across them is also clearly limited, presenting easy targets to enemy forces. Muscle fatigue will markedly decrease weapon accuracy, requiring a far greater weight of fire (and yet more weight to be carried).
The graph on the right shows walking speed energy use at different external loads, from 20kg to 50kg. If the reference is a 20Kg external load, 3km/hr on a flat firm surface, increasing the weight to 30kg results in an energy requirement increase of 12% but if the weight is increased to 50kg, it goes up by 50%. This can be translated into rules of thumb for weights and speeds, characterised by the table below.
Duration task, terrain, climate, altitude and individual fitness will all have an influence but as one might expect, more weight makes every task harder and/or slower. Recent studies (Silk 2010) demonstrated an average decrease in soldier mobility performance of 1,5% for every 1kg carried. Another study (Basaan 2005) looked at the time to complete an obstacle course and found that for every 1kg increase in external load (between 15 and 42kg) the time to complete increased by just under 8 seconds.
Terrain accessibility is also a significant factor for overburdened personnel, the images above show soldiers having trouble crossing even small gaps unaided, speed across them is also clearly limited, presenting easy targets to enemy forces. Muscle fatigue will markedly decrease weapon accuracy, requiring a far greater weight of fire (and yet more weight to be carried).
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