The effects of saddle height and power output on lower-limb muscles and joints during cycling

Cyclist numbers have risen sharply in the past decade, but overuse injuries are common. Proper saddle height and power output help prevent injuries by influencing riding posture and exercise intensity. This study examines how saddle height and power output affect lower limb loading, focusing on muscle forces and joint contact forces.

Twenty-five participants cycled under nine riding conditions (three saddle heights × three power outputs). A musculoskeletal multibody model, incorporating detailed lower-limb muscles, was driven by marker trajectories and pedal forces and torques. Generalized estimating equations were used to assess the effects of saddle height and power output, adjusted for gender, BMI, and cadence. The mean muscle forces and the maximum joint forces during a cycle were examined. The degrees of association were estimated by the Wald statistic for a power output × saddle height interaction term. The outcomes for each cycling condition were compared against those of the null models. The significance was p < 0.05 with Holm‒Bonferroni correction for post hoc comparisons.

The predicted muscle activations were in good agreement with the electromyography data, which verified the model. Greater power outputs increased hip/knee extensor forces and joint forces (β = 0.021–0.065, p ≤ 0.026) but decreased ankle plantar flexion and joint forces (β = -0.041 – -0.038, p ≤ 0.019). Higher saddle heights decreased the flexion angles of the hip and knee and the dorsiflexion of the ankle. It further reduced the mean muscle forces (β = -0.355 – -0.096, p ≤ 0.026), including rectus femoris, vastus lateralis and medialis, gastrocnemius, and gluteus maximus, except for the tibialis anterior (β = 0.294, p = 0.015), and lowered most of the maximum directional joint forces (β = -0.064 – -0.126, p ≤ 0.045).

The lower-limb joints were in a more flexed position at lower saddle heights, and higher power outputs and lower saddle heights increased kinetic load on lower-limb muscles and joints. Therefore, moderate power output with a higher saddle setting may be preferable. However, optimal adjustments should also consider other factors not examined in this study, such as saddle pressure.