Character animations produced with motion capture data have many of the stylistic details seen in human motion while those generated with simulation are physically realistic for the dynamic parameters of the character. We combine these two approaches by tracking and modifying human motion capture data using dynamic simulation and constraints. The tracking system generates motion that is appropriate for the graphical character while maintaining characteristics of the original human motion. The system imposes contact and task constraints to add dynamic impacts for interactions with the environment and to modify motions at the behavior level. The system is able to edit motion data to account for changes in the character and the environment as well as create smooth transitions between motion capture sequences. We demonstrate the power of combining these two approaches by tracking data for a variety of upper-body motions and by animating models with differing kinematic and dynamic parameters.