Effects of Small and Normalized Q-Factor Changes and Knee Alignment on Knee Biomechanics during Stationary Cycling

Increasing inter-pedal distance (Q-Factor: QF) in cycling increases peak internal knee abduction moments (KAbM). The effect of smaller and normalized changes in QF has not been investigated. The purposes of this study were to examine changes in KAbM with small and normalized increases and whether static knee alignment accounts for any changes in knee biomechanics in cycling. Fifteen healthy participants were included (age: 22.7 ± 2.5 years, BMI: 23.95 ± 3.21 kg/m²). Motion capture and instrumented pedals collected kinematic and pedal reaction force (PRF) data, respectively, while participants cycled at five different QFs. Each participant's mechanical axis angle (MAA) was estimated using motion capture. Each participant's QFs were normalized by starting at 160 mm and increasing by 2% of the participant's leg length (L), where the five QF conditions were as follows: QF1 (160), QF2 (160 + 0.02 × L), QF3 (160 + 0.04 × L), QF4 (160 + 0.06 × L), and QF5 (160 + 0.08 × L). A linear mixed model was performed to detect differences between QF conditions. KAbM increased by more than 30% in QF5 from QF1, QF2, QF3, and QF4. Medial PRF increased by at least 20% in QF5 from QF1, QF2, and QF3. MAA had varying degrees of correlation with the variables of interest. These results suggest that KAbM is more sensitive to changes in QF at greater QF increases.