Biomechanical analysis of knee flexion and saddle height adjustment on knee pain in amateur cyclists

Abstract

Introduction: Cycling is increasingly popular worldwide owing to its health, transportation, and environmental benefits. However, overuse injuries are common, with the knee being the most frequently affected joint. Among these, anterior knee pain—often related to excessive knee flexion at bottom dead center—is particularly prevalent in amateur cyclists. Proper bicycle fitting, especially saddle height adjustment, has been suggested as a preventive measure, yet few studies have examined its short- and medium-term effects on pain reduction. This study investigated the relationship between knee flexion angle and the impact of saddle adjustment on knee pain in amateur cyclists. Materials and Methods: A longitudinal, quantitative, correlational study was performed with 38 male amateur road and mountain bike cyclists aged 25–57 years. Participants were divided into two groups according to knee flexion angle: >40° (n = 21) and <40° (n = 17). Knee pain was evaluated using a Visual Analog Scale (VAS) at three time points: before adjustment, immediately after saddle fitting, and two weeks after adjustment. Sagittal plane kinematics were analyzed through video recordings with reflective markers using Kinovea software. Statistical analyses included t-tests, ANOVA with Tukey post-hoc comparisons, and Spearman's correlation, with significance set at p < 0.05. Results: Cyclists with knee flexion >40° reported significantly higher pain than those with <40° (VAS 4.4 ± 1.9 vs. 0.9 ± 1.5, respectively, p < 0.001). Following saddle adjustment, flexion angles decreased to 25°–30°, accompanied by significant pain reduction both immediately (VAS 2.7 ± 1.4) and after two weeks (VAS 1.4 ± 1.6). A strong correlation was found between knee flexion angle and pain before adjustment (r = 0.72), which disappeared after bike fitting. No significant changes were observed in the <40° group. Discussion: The findings confirm that excessive knee flexion (>40°) is strongly associated with greater pain perception in cyclists, likely owing to increased patellofemoral compressive forces and altered tendon mechanics. Saddle fitting proved effective in reducing pain and optimizing knee biomechanics, aligning with previous studies that recommend a bottom dead center flexion angle of 25°–30°. Conclusions: Knee flexion angle is a key determinant of knee pain in amateur cyclists. Angles exceeding 40° increase the risk of discomfort, whereas saddle height adjustments that achieve a flexion angle of 25°–30° significantly reduce pain both immediately and over time. Therefore, proper bike fitting should be considered an essential preventive and therapeutic strategy to minimize overuse-related knee injuries in cyclists.