| Description |
Marching while carrying a backpack load is the most common activity in the army so being able to endure such a task is required of all military personnel. It is a predictable source of common injuries. Lower limb injuries in particular are caused not only by the extra load but also by the type of surface on which the soldier marches. The objective of this study was thus to expand on the current knowledge of the biomechanical effects of loads by investigating lower limb gait parameters on a sand surface while carrying a military backpack. Twenty healthy male participants were recruited from among students at the University of Utah who fit the current U. S. military recruitment criteria. The independent variables controlled were the surface type (i.e. hard and sand), slope (i.e. flat and slant), backpack type (i.e. no load, MOLLE, and ALICE), and marching speed (i.e. self-selected and 4 km/h). Data acquisition was performed using 16 NaturalPoint cameras, AMASS software, and 4 force plates. Over all, it was observed that a decrease in cadence, a decrease in stride length, and an increase in double support time occurred as load was added. In terms of the effects of slope, an increase in double support time and a decrease in stride width were found to occur on the slanted surface as compared to the flat surface. As for the effects of surface type, a decrease in cadence, double support time, and stride length was observed on the sand surface as compared to the hard surface. There was also found to be a general iv increase in ankle dorsiflexion/plantarflexion, knee flexion/extension, and hip abduction/adduction RoM (Range of Motion) angle on the sand surface as compared to the hard surface. On the whole, walking on a sand surface thus increased M/L GRF, increased vertical impact force, decreased vertical thrust force, and increased knee abduction/adduction moment. No difference was detected between the MOLLE and ALICE backpacks in terms of resulting cadence, double support time, and stride length. However, a statistically significant increase in stride width was observed with the MOLLE as compared to the ALICE pack. The MOLLE also influenced a statistically significant increase in hip abduction/adduction RoM angle as compared to the ALICE. The ALICE backpack in turn resulted in increased hip A/A moment and higher braking/propulsive forces. Although all of these differences were statistically significant, they are not substantial enough to be considered practically meaningful. From the findings of this research, it is recommended that military training and general operations be minimized in sand environments in order to reduce the injury potentials discussed above. In unforeseen or unavoidable cases where exposure to such terrain is prolonged, reducing overall load thus needs to be considered to reduce injury potential. |
