Biomechanical analysis of stair walking patterns and their implications for knee health in young males

Stair ambulation is an essential daily activity associated with maintaining mobility and musculoskeletal health, and its biomechanical characteristics may influence fall risk. This study aimed to examine how different stair-walking strategies-single-step and double-step ascent-affect peri-knee muscle forces and joint loading using OpenSim-based musculoskeletal simulations, thereby providing biomechanical insights for public health-oriented interventions in injury prevention and rehabilitation.

Synchronized kinematic and kinetic data were imported into OpenSim musculoskeletal models to compute knee joint angles, joint reaction forces, and peri-knee muscle forces. The simulated muscle activation levels were then compared with synchronized surface electromyography (sEMG) signals to validate the reliability of the simulations.

Results indicated that the double-step stair ascent mode produced significantly greater step length (p = 0.001) and larger peak hip (p = 0.002) and knee (p = 0.015) flexion compared with the single-step mode. Continuous-time SPM analysis further revealed that knee flexion remained significantly higher in the double-step mode throughout most of the single support phase (p < 0.001), while no significant differences were observed in knee joint reaction forces (p > 0.05). Muscle force analysis showed that quadriceps muscle force, including the quadriceps components (vastus medialis/lateralis/intermedius and rectus femoris) was significantly greater in the double-step mode during the early stage of the single support phase (p < 0.001). For the hamstrings, only the biceps femoris long head demonstrated significant differences between modes (p < 0.001), whereas the biceps femoris short head, semimembranosus, semitendinosus, and gastrocnemius showed no significant differences (p > 0.05).

Double-Step Mode increased step length, hip mobility, and quadriceps activation without significantly elevating knee joint forces, supporting knee stability under higher mechanical demands. From a public health perspective, stair walking may enhance lower-limb muscle engagement and potentially contribute to the maintenance of balance control and mobility, while Single-Step Mode may be safer for individuals with knee impairments by minimizing joint stress and supporting rehabilitation.