Article 1 adult 1 age difference 1 aged 1 aging 1 ankle power generation 1 controlled study 1 coordination 1 electromyogram 1 electromyography 1 female 1 gait 1 human 1 intersegmental coordination 1 kinematics 1 locomotion 1 male 1 moving upward and downward 1 muscle activation 1 muscle activity analysis 1 muscle contraction 1 musculoskeletal system parameters 1 nervous system parameters 1 neuromechanics of gait 1 neuromuscular function 1 physical activity 1 population structure 1 range of motion 1 spinal motoneuronal output stair and slope 1