The Effects of Obesity on the Biomechanics of Gradient Walking

Abstract

Walking is a popular form of exercise for the prevention and treatment of obesity. However, walking may be a source of biomechanical loads that link obesity and musculoskeletal injury and pathology. During level walking, obese adults may adopt a more erect gait pattern (less knee flexion during stance) that reduces lower extremity net muscle moments (NMM, Nm/kg) compared to non-obese individuals. Walking uphill requires greater hip and knee NMM, but the effects of obesity on the biomechanics of uphill walking are not known. PURPOSE: To quantify the biomechanics of level and gradient walking in obese and non-obese adults. METHODS: Twelve obese, 100.5 (15.7) kg, 33.4 (2.4) kg/m2, (mean (SD)) and eleven non-obese, 68.3 (11.5) kg, 22.0 (2.0) kg/m2 adult volunteers participated in this study. We measured ground reaction forces and three-dimensional lower extremity kinematics while subjects walked on a dual-belt force measuring treadmill at 1.25 m/s with the treadmill grade set at -3, 0, 3, 6 and 9°. We calculated NMM at the hip, knee and ankle. RESULTS: During uphill vs. level walking, all participants walked with greater hip and knee flexion and ankle dorsiflexion during early-mid stance. Peak hip flexion (heel strike) was greater in the obese vs. non-obese when walking up the steeper grades (55 vs. 45° at 6° and 57 vs. 39° at 9°, respectively). Compared to level walking, knee joint range of motion during early stance increased during downhill and decreased during uphill walking, with no differences between the groups. Absolute early-stance hip and knee extensor NMM were greater in obese individuals and increased when walking uphill vs. level walking. Peak early-stance hip extensor NMM in the obese and non-obese adults were 0.78 vs. 0.88 Nm/kg, respectively, during level walking and increased to 1.24 vs. 1.19 Nm/kg, respectively, while walking up the 9° incline. Peak early-stance knee extensor NMM in the obese and non-obese adults were 0.3 vs. 0.37 Nm/kg, respectively, during level walking and increased to 0.71 vs. 0.54 Nm/kg, respectively, while walking up the 9° incline. CONCLUSIONS: While obese adults may be able to walk on level ground with relatively small joint loads, our results suggest that their joint loads increase disproportionally compared to non-obese adults when they walk uphill.