Determining the force and moment components transmitted by the knee is useful both to understand the etiology of over-use knee injuries common in cycling  and also to assess how well different interventions protect against over-use injury. Because the loads thought to be primarily responsible for over-use knee injury are the non-driving moments (varus/valgus and internal/external axial moments) transmitted by the knee , a 3-D model is necessary for calculating these loads. To our knowledge, no study has developed a model that includes complete 3-D kinematics of the segments to calculate these loads. Consequently one objective of this study was to develop a complete, 3-D model to calculate the intersegmental knee loads during cycling. A second objective was to use this model to examine how simplifying assumptions affect the 3-D knee loads.