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There is an increase in participation levels in sporting activities, paiticularly of the high intensity variety. With this comes an increase in joint injmies. Subchondral and interfacial tidemark injmies (osteochondral fracture) caused by high intensity activities as well as motor vehicle injures also continue to cont1ibute significantly to such joint injuries. The rate of loading is a significant contributing factor in type of injury. It is therefore important, for injury prevention and health management reasons, to establish loading rates that present a high risk of osteochondral fracture in human joints. Youth participation in high level spent and training is a relatively new phenomenon, and one of concern due to the developing musculo-skeletal systems of these athletes. Joint injuries to this subgroup can cause osteochondritis dissecans and are thought to lead later to joint conditions such as osteoarthritis. These joint conditions have heavy psychological and financial implications, and enforce a resulting burden on health services. It has already been established through clinical studies and laboratory experiments that the plane of fracture of articular cartilage is through the tidemark in mature tissues and through the osteochondral region in immature joints. This study goes on to establish the strain-rate dependence, with respect to fracture toughness, of mature and immature articular cartilage under conditions that rigorously model joint conditions. There is a pronounced, in-plane, fibrillar arTangement in the articular surface that causes localised forces to expand the articular matrix laterally. This causes high tensile stresses with the potential to fracture the continuity of the matrix and produce radial clefts, which penetrate down into the underlying matrix. It has previously been found that this is most pronounced under high velocity loading where there is insufficient time for the water to exude from the matrix. The response of articular cartilage a