Impact of Body Weight on Stair Ascent and Descent Biomechanics in Teenagers

This study explored the impact of body weight on relative ground reaction forces (rGRF) and kinematic parameters during stair ascent and descent in 80 adolescent males (aged 16–17), categorized by WHO BMI criteria. Participants completed tasks on a standardized three-step staircase, with simultaneous collection of ground reaction forces and video data. Three-dimensional motion and rGRF data were analyzed to extract kinetic and kinematic measures. Statistical Parametric Mapping (SPM) was used to assess group differences across the movement cycle. Obese participants showed significantly lower rGRF values than the underweight group during the forward continuance phase of stair descent. Underweight individuals had greater knee flexion angles than overweight and obese peers in the controlled lowering phase. The normal weight group showed higher hip flexion during left foot ascent than the obese group. In the sagittal plane, underweight individuals displayed greater hip-ankle distances during the pull-up phase of right foot ascent. Normal weight participants had greater hip-ankle distances during right foot descent than overweight and obese peers. In the frontal plane, obese participants showed reduced hip-ankle distances during weight acceptance and pull-up phases. These results highlight BMI-related biomechanical differences during stair tasks in teenagers.