Factors that affect cartilage composition are crucial to understanding the disease mechanisms in knee OA. A multi-scale approach towards understanding the knee OA disease process by evaluating tissue compositional changes, joint contact mechanics, whole-body neuromuscular dynamics, and functional performance. The results will be the first to show the association between cartilage composition and daily function (performance and patterns) which are implicated in OA development and progression. With the addition of comprehensive muscle testing (cross sectional area/volume assessment using MR, strength testing, muscle activation and co-contraction patterns during daily activities), it will be possible to study the interaction between all major tissues around the knee.