Introduction: Knee osteoarthritis (KOA) is a degenerative joint condition that affects both the medial and lateral femoral condyles, and is a leading cause of pain and reduced mobility worldwide. Low-impact exercises such as cycling are increasingly explored, as cycling reduces knee joint contact forces (KJCF) compared to high-impact activities, making it a suitable option for preserving joint health. Understanding the distribution of KJCF across the medial and lateral condyles during cycling is crucial for informing effective exercise interventions.

Objective: This study aims to validate an existing musculoskeletal cycling model using experimental electromyography (EMG) data, and to extend it to estimate the distribution of the tibiofemoral compressive force (TFC) across the medial and lateral condyles.

Methods: Eleven healthy recreational cyclists (mean age: 25.7 ± 1.7 years) participated in lab-based cycling trials. Reflective markers and EMG sensors captured lower limb kinematics and muscle activity at varying cadences (70–90 RPM) and power outputs (80–120 W). The musculoskeletal cycling model of Clancy et al. (2023) in OpenSim was modified to include separate medial and lateral knee compartments. A publicly available dataset was used to scale the modified model and run inverse kinematics (IK), static optimisation (SO), and joint reaction force (JRF) analysis. Predicted muscle activation was evaluated using five matched comparison pairs and cross-correlation analysis. Finally, the modified model was used to estimate the distribution of TFC across the medial and lateral condyles throughout the crank cycle.

Results: The modified model produced near-identical results compared to the original model in both muscle activation (R > 0.99) and total TFC (R > 0.98), verifying the model modifications.
Model-predicted muscle activations showed the highest correlation with EMG data for the vastus medialis (VM) (R = 0.88–0.99) and the vastus lateralis (VL) (R = 0.84–0.99). Lower correlations were observed for the rectus femoris (RF), gastrocnemii (GL, GM), biceps femoris (BF), and semitendinosus (ST). In all subjects, lateral TFC consistently exceeded medial TFC throughout most of the crank cycle.

Conclusion: This thesis successfully estimated compartmental TFC during cycling without affecting the muscle activations or total TFC predictions. Comparison with EMG data showed variable agreement, reflecting modelling limitations and inter-subject variability. The results provide valuable insight into asymmetrical knee joint loading during cycling and illustrate the potential of musculoskeletal modelling to guide more targeted rehabilitation strategies for individuals with KOA.