Increasing Body Weight Alters Lower Limb Muscle Balance And Foot Control

Abstract

Obesity is a well established risk factor for developing osteoarthritis (OA). Population-based studies in particular have consistently shown a link between obesity and knee OA. Yet many factors for diseases and conditions associated with obesity could contribute to OA initiation and/or progression. The present study examined the effects systematically increasing subject weight and the effects on quadriceps femoris muscle function and foot balance stability during walking and squatting. METHODS: Twenty asymptomatic healthy young adults (Age = 22 ± 2; 19 kg/m(2) < BMI < 22 kg/m(2)) were studied. A three-dimensional gait analysis was conducted for all subjects. Plantar pressure distribution (the peak pressure of the eight plantar surface areas) and foot kinematics, surface electromyograms from the lateral and medial gastrocnemii, lateral and medial hamstrings, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) were recorded during squatting and self-selected speed walking. Weight increase (10, 20 and 30% of subject body weight) was achieved by placing a belly bag on the subject’s body attached around the hip and to the shoulders. Principal component analysis was used to extract major features of amplitude and temporal pattern variability from the electromyograms of each muscle group (gastrocnemii, quadriceps, hamstrings separately). Analysis of variance models tested for weight load effects and interaction effects for these features (α = 0.05). RESULTS: Significant weight load effects were found for features that described more prolonged activation of the gastrocnemii and quadriceps muscles during the stance phase of gait (P < 0.05). Load increase selectively activated the VL compared to the VM during walking and the first 20 degrees of knee flexion during the squat. Load increase was also associated with increased mid-rear-foot pressure and delay in both the onset of the second wave of flexion at the knee joint and reduced range of motion of the ankle (P < 0.05). CONCLUSIONS: We confirm the effects of increasing body weight on lower extremity muscle activation and foot balance control, both of which may contribute to knee OA development and progression.