How saddle height parameters alter the lower extremity motion patterns during the cycling: The musculoskeletal modeling study

Bicycle components that come into direct contact with people’s bodies have the potential to directly affect the musculoskeletal system. Saddle heights are a significant cycling variable. Controlling the saddle height has a significant impact on balance control and lower limb joint stability. The current study aimed to compare the kinematics of the lower extremities for varying saddle heights during cycling using musculoskeletal modeling. This study included twenty professional cyclists (mass: $75.3 \pm 6.5$ kg, height: $180 \pm 6.3$ cm, age: $28.5 \pm 6.5$ years). The markers were measured using twelve Vicon motion captures (Vicon MX, Oxford, UK, 100 Hz). The bicycle’s output power was measured with a smart trainer (Tacx Flux, Netherlands). Each subject’s inseam quantity—the measurement made between the top of the thigh and the ankle—was multiplied by 0.883 to determine the standard saddle height that was selected as a lower saddle. When cycling begins, the crank angle (CA) is at CA=0°, which is the highest position of the right crank (when the right toe is at its highest height). OpenSim’s scaling tool generated a subject-specific musculoskeletal model for each subject. The joint angles in two saddle height positions were computed using OpenSim’s inverse kinematics tool. Saddle heights primarily affect the lumbar spine, pelvis, hip, and ankle kinematics. They significantly alter the hip and lumbar spine joints’ motion patterns; for example, the range of motion for the upper and lower saddles’ hip abduction-adduction was $10.65 \pm 0.83$ and $4.17 \pm 3.23$, respectively. Additionally, the range of motion (ROM) for the lumbar spine bending in the upper and lower saddles were, respectively, $1.99 \pm 1.40$ and $6.75 \pm 5.64$. These findings demonstrated that human joints accept the kinematics chain and that modifications to one joint also affect adjacent joints.