1C1-3 The Effect of Carrying a Military Backpack on a Transverse Slope and Sand Surface on Lower Limb Kinetics

Abstract

The objective of this study was to understand gait kinetics while walking on a sand surface (vs. hard surface) with wearing a traditional military ALICE backpack (vs. modularized MOLLE backpack). Twenty healthy male students participated in this study. Each participant completed a total of 72 trials (3 good trials for each testing configuration). These testing conditions were combinations of two surface types (hard, sand), two transverse slopes (flat, 10°), two walking speeds (self-selected, 4 km/h), and three load conditions (no load, MOLLE, ALICE). Walking on sand surface required a greater medial-lateral ground reaction force and a greater maximum vertical impact force. Sand surface gait also resulted in a greater mean knee abduction/adduction moment. Hard surface gait resulted in a greater maximum vertical thrust force, a greater maximum braking force, and a greater maximum propulsive force. In terms of backpack effect comparison, mean hip abduction/adduction moment was greater while wearing the ALICE than the MOLLE. These results suggest that walking on sand with a backpack may increase the potential for injuries from overuse and falls. Hard surface walking on the other hand may increase the risk of foot strain and foot blisters.

Ground reaction forces and muscle activity while walking on sand versus stable ground in individuals with pronated feet compared with healthy controls

“…The observed reduction in peak anterior GRF amplitudes during the push off phase while walking on sand may be representative of foot and ankle instability due to impairment of the midtarsal locking mechanism in the late stance phase which provides an adequate lever to push off against. It has previously been reported that walking on stable ground compared with walking on sand results in a greater maximal braking force and maximal propulsive force in healthy male students aged 18–30 years [29]. Of note, we did not find any significant main effects of “surface” for peak medio-lateral GRFs.…”

“…The alignment tabs ensured that all shear forces were transmitted to the surface of the force plate. Previous studies confirmed that this force plate construction embedded into the walkway is well-suited to reduce dissipation of force and to accurately identify forces while walking on the two surface conditions [29–32]. Test-retest reliability was assessed for GRF and EMG data and revealed intra-class correlation coefficients (ICC) > 0.6 and 0.53, respectively.…”

“…Of note, we did not find any significant main effects of “surface” for peak medio-lateral GRFs. However, a previous study has demonstrated that walking on sand resulted in larger medio-lateral GRF in healthy male students aged 18–30 years [29].…”

The influence of deformation height on estimating the center of pressure during level and cross-slope walking on sand

“…The alignment tabs ensured all shear forces were transmitted to the surface of the force plate. Previous studies confirmed that this force plate isolation technique could serve well to reduce the dissipation of force and accurately identify measured GRF on ballast and sand [5,8].…”

“…Lejeune et al investigated the mechanics and energetics of human locomotion on sand [4]. The studies performed by Kim and Yoo analyzed upper and lower limb biomechanics when carrying a military backpack while walking on cross-slope sand surfaces [5,6]. Other studies have focused on the effects of walking on gravel, like railroad ballast.…”