In this paper we present a general method for rapid prototyping of realistic character motion. We solve for the natural motion from a simple animation provided by the animator. Our framework can be used to produce relatively complex realistic motion with little user effort. We describe a novel constraint detection method that automatically determines different constraints on the character by analyzing the input motion. We show that realistic motion can be achieved by enforcing a small set of linear and angular momentum constraints. This simplified approach helps us avoid the complexities of com- puting muscle forces. Simpler dynamic constraints also allow us to generate animations of models with greater complexity, performing more intricate motions. Finally, we show that by learning a small set of key parameters that describe a character pose we can help a non-skilled animator rapidly create realistic character motion.