Effective methods of load carriage are needed by the military to reduce injury and maintain soldier readiness. The most common injuries resulting from load carriage are lower extremity overuse injuries and lower back injuries. The Army Torso Borne Load Assistance System (ATLAS) is an experimental device designed at the US Military Academy to redistribute the weight of a torso-borne load to the hips. ATLAS uses three flexible struts to transfer the load of body armor to a hip belt, utilizing the larger hip and leg muscles to support. The purpose of this study is to determine the impact of ATLAS on hip and shoulder comfort, and kinetic variables that have been previously associated with lower back injury: loading rate, peak ground reaction forces (pGRF) in the vertical, medial, and lateral directions, and total vertical impulse. It is hypothesized that ATLAS will decrease the magnitude of kinetic variables and comfort in the hips, but increase comfort in the shoulders.
Ten college-age subjects (178 +/- 8 cm, 80 +/- 10 kg) walked on a treadmill at a speed of 1.5 m/s for seven minutes with a 45 lb. load consisting of weighted body armor and ATLAS. This study was IRB approved, and all participants provided informed consent. Two trials were conducted in a randomized order: with the device engaged, and without it engaged (hip belt unclipped around waist). Three-dimensional ground reaction force data were sampled at 1000 Hz and used to calculate the variables of interest. Comfort data were collected at the shoulders and hips using a 100mm visual analog scale. The trials were analyzed with a paired, two-tail t-test with significance set at p<0.05.
ResultsATLAS had no significant impact on the kinetic variables investigated, although there was a significant difference in comfort ratings (Figure 1).
As indicated by the comfort scores, the participants were clearly able to detect the weight shift provided by the ATLAS device. However, ATLAS does not appear to impact gait variables that have been previously associated with back and lower extremity injury susceptibility. Subject-by-subject analysis showed no trend in the effect of engaging the device on the kinetic variables; some individuals increased while others decreased, and all changes were of small magnitude. Although ATLAS does not appear to affect the gait variables measured in this study, it is unclear if this device is effective at alleviating spinal loading. Further studies should directly investigate the changes in trunk loading with this type of device.
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