The objective of this study was to test the hypothesis that static loading (squatting at a 90 degrees angle) and dynamic loading (30 deep knee bends) cause different extents and patterns of patellar cartilage deformation in vivo. The two activities were selected because they imply different types of joint loading and reflect a realistic and appropriate range of strenuous activity. Twelve healthy volunteers were examined and the volume and thickness of the patellar cartilage determined before and from 90 to 320s after loading, using a water excitation gradient echo MR sequence and a three-dimensional (3D) distance transformation algorithm. Following knee bends, we observed a residual reduction of the patellar cartilage volume (-5.9+/-2.1%; p<0.01) and of the maximal cartilage thickness (-2.8+/-2.6%), the maximal deformation occurring in the superior lateral and the medial patellar facet. Following squatting, the change of patellar cartilage volume was -4.7+/-1.6% (p<0.01) and that of the maximal cartilage thickness -4.9+/-1.4% (p<0.01), the maximal deformation being recorded in the central aspect of the lateral patellar facet. The volume changes were significantly lower after squatting than after knee bends (p<0.05), but the maximal thickness changes higher (p<0.05). The results obtained in this study can serve to validate computer models of joint load transfer, to guide experiments on the mechanical regulation of chondrocyte biosynthesis, and to estimate the magnitude of deformation to be encountered by tissue-engineered cartilage within its target environment.