The Navy SEAL Physical Fitness Guide - Uniformed Services ...

Biomechanics of Load-BearingThe duration of time your foot is on the ground during a normal gait does notincrease until pack loads are greater than 50% of your body weight. However, the length oftime your foot is in the air during the swing phase of your gait decreases with increasingload-bearing weight. This response occurs to increase the length of time both feet are onthe ground for double support. As the load weight increases, your feet increase the groundforce downward, forward, rearward and in lateral directions. Shorter stride lengths willincrease stride frequency and help maintain normal walking patterns during moderate toheavy load-bearing.Shorter strides may minimize strain and possiblyreduce lower back and lower extremity injuries.Load-Bearing and Walking PaceSelf-pacing during load-bearing results in a lower energy cost than a forced-pace.However, not all missions allow self-pacing. When the pace is forced, a self-selecteddecrease in walking pace will be observed as the load-bearing weight increases. The selfselectedwalking pace or exercise intensity during load-bearing depends on many factors.Some of the factors affecting the self-selected pace include:" Load weight" Aerobic fitness level (maximal aerobic capacity)" Total distance walkedYou will normally self-pace at 30% - 35%of your maximal aerobic capacity whencarrying a moderate load of 50 pounds.With lighter loads, self-pacing normally results in an exercise intensity of around45% of your maximal aerobic capacity. However, an exercise intensity of 60% or greatercan be achieved when the load is light and the distance short. Remember: walking paceand load weight carried during an infiltration or exfiltration contribute to the rate ofexhaustion. Figure 10-1 presents estimates of when exhaustion might occur at variouswalking speeds and loads. High rates of energy expenditure (900 to 1000 calories per hour)can be sustained for only 6 to 10 minutes. To be able to move quickly at this intensity, loadweight must be light.The Navy SEAL Physical Fitness Guide 177