the classical contrapposto pose consists of the figure standing with one leg holding the majority of the weight and the other leg relaxed. it is a slouched, and natural sort of pose.
benvenuto cellini's perseus also stands with weight on one leg, but this is from him stepping forward, in action, rather than resting on his leg. this results in less curve of the chest angle in the shoulders, and conveys less relaxing message.
hope that helps :)
