Effects of Carrying a Loaded Energy Harvesting Backpack on Trunk Lean: 2611 Board #131 June 2 9

Soldiers are fielded with a wide range of loads to carry including battery powered electronic devices. An energy harvesting backpack (EHB) was developed to convert gait kinetic energy into electrical power, providing a power source to recharge batteries and reduce the load of extra batteries carried in standard backpacks. Little is known about the kinematic effects of carrying the EHB compared to the military standard assault pack (AP). PURPOSE: To determine if trunk lean changes when carrying the EHB compared to the AP and whether these changes are affected by pack, load, and speed. METHODS: Sixteen subjects (28.6±4.7 years; 173.9±10.1 cm; 76.9±16.1 kg) walked on an instrumented treadmill under 8 combinations of pack, load, and speed conditions each for 5 minutes. Conditions included 1) pack: AP and EHB, 2) load: 7.9 kg (light) and 15.9 kg (heavy), and 3) speed: 1.34 m/s and a self-selected faster speed. Due to its design, the empty EHB mass was 4.4 kg greater than the AP. Kinematic data were collected to calculate trunk lean relative to the vertical axis (degrees). A 3-way repeated measures ANOVA was used to determine effects of pack, load, and speed on trunk lean with an alpha level set a priori at p<0.05. Post-hoc pairwise comparisons were performed with Bonferroni corrections. RESULTS: A significant main effect of speed on trunk lean (F1,13=44.1, p<0.001) was observed where forward lean was greater at faster speeds (Slow: 3.8±0.6; Fast: 7.5±0.7, F1,13=44.1, p<0.001). There was a significant pack x load interaction on trunk lean (AP-Light: 1.4±2.1; AP-Heavy: 4.6±2.3; EHB-Light: 5.5±2.9; EHB-Heavy: 10.9±3.4; F1,13=15.5, p=0.002). Subjects using the EHB walked with greater increase in forward lean when carrying the heavy load. CONCLUSION: Walking with heavy loads and carrying the EHB produced greater increase in forward lean when compared to the AP. This suggests a potential nonlinear effect of pack and load on trunk lean. The weight cost or oscillation of the EHB may also contribute to these changes in gait. Phase relationships between the user and EHB centers-of-mass could be examined in future research to study the effects on gait biomechanics. Further analysis is also warranted to determine tradeoffs in power generated from the EHB and Soldier biomechanics while walking with the system.