Gait, foot structure, and muscle strength in obese children: further steps towards evidence informed care

Childhood obesity is an increasing problem in the UK and co-morbidities of obesity are increasingly evident. Previous research has suggested altered musculoskeletal function including; lower limb and foot biomechanics, muscular strength and plantar pressures in obese children compared to healthy weight peers. However, there has been limited research to quantify the associations between weight status and excessive body fat mass with musculoskeletal function. The primary aim of this research was to explore lower limb and foot biomechanics, plantar pressures and lower limb strength in 7-to-11 year old children. Sixty-nine children were recruited to participate in protocols for; body composition, three-dimensional gait analysis of the lower limb and foot, plantar pressures and strength assessment of the hip, knee and ankle. Principal component analysis was undertaken to determine regression scores representing elements of the gait cycle to be further analysed. Strength variables and regression scores were entered into MANCOVAs to assess the difference between Z score derived overweight/obese and healthy groups. Multiple regression was undertaken to assess the relationships between lower limb and foot variables, plantar pressures, and strength with body fat. There was no difference in lower limb kinematics or foot segment angles between groups. Overweight/obese group had increased sagittal knee moment and frontal power. The overweight/obese group were stronger and more powerful in absolute terms in ankle dorsiflexion and knee extension and flexion. When strength was normalised to body mass, fat mass and fat free mass, overweight/obese were weaker and less powerful. Body fat had no effect on lower limb kinematics but significantly effected metatarsals, midfoot and calcaneus angular motion. Body fat significantly increased ankle, knee and hip moment and powers. Midfoot and forefoot plantar pressure was significantly predicted by body fat. As body fat increased absolute strength in the knee extensors, flexors and ankle dorsiflexors increased. Strength normalised to body mass decreased with increasing body fat. Body fat significantly predicted (as body fat increased strength decreased) strength normalised to fat free mass in all muscle groups except isokinetic ankle dorsiflexors. This work demonstrates the need to use appropriate parameters for investigations into the effects of obesity. BMI-derived weight categorisation makes the findings easily relatable back to a clinical population, but it produces less significant findings compared to a direct measure body fat. The overall findings are that overweight/obese children are relatively weaker and have increased loading of lower limb and foot joints during gait. This work demonstrates the need to understand the effects of obesity on musculoskeletal function to aid clinical rehabilitation and reduce the health burden in later life.