INTRODUCTION:​ Children are encouraged to participate in at least 60 minutes of moderate to vigorous physical activity (MVPA) daily. Active transport, such as walking to school daily, may be a convenient way for children to accrue physical activity as long-duration (e.g. >​30 minutes), moderate intensity activities have been cited as an effective way to reduce body fat. However, typical walking speeds do not elicit a moderate intensity in nonobese children and the slower self-selected walking speeds of obese children may not elicit a moderate intensity physiological response. In addition, obese children have a smaller aerobic capacity, are relatively weaker and walk with altered gait biomechanics, suggesting they may fatigue during longer bouts of walking and have a correspondingly greater risk of musculoskeletal injury when walking for physical activity. It is currently unknown how physiological intensity and gait characteristics change with walking duration in either obese or nonobese children.

PURPOSE:​ The purpose of this study was to investigate the effect of a continuous bout of walking on the energetics and mechanics of nonobese and obese children. METHODS:​ Thirty-four children (21 nonobese, 13 obese) walked on a dual-belt force measuring treadmill at 1.00 m/s for 20 minutes. Metabolic, kinematic, and kinetic data were collected at the 6th, 10th, and 19th minute of the trial.

RESULTS:​ We found a significant effect of obesity, but not walking duration, on metabolic parameters. Obese children exhibited greater absolute and lean-mass-normalized metabolic rates, but similar mass-specific metabolic rates compared to the nonobese children. Conversely, we found an effect of walking duration on lower extremity joint angles and net muscle moments. Hip abduction angles in both early and late stance increased, and both hip and knee extension and hip abduction net muscle moments were greater at the end versus the beginning of the trial. While the magnitude of the changes was similar between groups, we found greater absolute net muscle moments at all joints in the obese group throughout the course of the trial.

CONCLUSION:​ This study suggests that obese children are able to accrue MVPA through engaging in walking at moderate speeds and that compared to nonobese children, obese children do not exhibit significantly greater changes in walking biomechanics during a 20-minute bout. Although our results suggest that obese children can walk at a moderate intensity for a relatively long duration, the effects of exposing the musculoskeletal system to this prolonged physical activity remain unknown.