Effects Of Load Carriage And Muscular Fatigue On Ground Reaction Loading Rate During Walking

Abstract

Military personnel are often afflicted by tibia stress fracture (TSF) during basic training. Load carriage and muscle fatigue may be factors related to the high incidence of TSF. Load carriage increases ground reaction force during walking. Muscle fatigue reduces muscles' ability to attenuate dynamic load on musculoskeletal system during locomotion. However, it is yet to be determined what effects load and fatigue may elicit in mechanical loading rate during walking. PURPOSE: To determine the effects of load carriage and fatigue on peak vertical ground reaction force and loading rate during walking. METHODS: Eighteen healthy males (age: 21 ± 2 yrs, body mass: 77.6 ± 9.6 kg, body height: 181 ± 4 cm) performed tasks in the following order: unloaded and unfatigued walking (UU), loaded and unfatigued walking with a 32 kg rucksack (LU), a fatiguing protocol consisting of stepping and heel-raising with a 16 kg rucksack, loaded and fatigued walking with a 32 kg rucksack (LF), and unloaded fatigued walking (UF). Each walking task was performed for 5 min on a force instrumented treadmill (AMTI) at 1.67 m/s. Peak vertical ground reaction force and loading rate at weight acceptance were normalized to body weight. One way repeated measures ANOVAs and pair-wise comparisons with Bonferroni correction were performed. α = 0.05. RESULTS: The peak vertical ground reaction forces of the UF (1.35 ± 0.11 BW), LU (1.92 ± 0.18 BW), and LF (1.99 ± 0.19 BW) were all greater than that of the UU (1.27 ± 0.06 BW) (p < 0.05). The peak vertical ground reaction loading rates of the UF (21.75 ± 7.92 BW/s), LU (35.29 ± 12.07 BW/s), and LF (37.58 ± 11.92 BW/s) were all greater than that of the UU (16.81 ± 3.40 BW/s) (p < 0.05). CONCLUSION: Fatigue, load carriage, and the combination of load carriage and fatigue all lead to significant increases of mechanical loading and loading rate on the lower extremities during walking. As great magnitudes of mechanical loading and loading rate are identified risk factors of TSF, the effects of load carriage and muscle fatigue could expose military personnel to increased risk of TSF during basic training. Interestingly, the increases of mechanical loading rate are more pronounce than that of the mechanical loading. Mechanical loading rate may have greater effect on the development of TSF than the loading magnitude. DOD#W81XWH-08-1-0587