Obesity is a growing health problem in the United States, especially among children. Indicators show that the rate of obesity for children age 12-19 years old has risen from 5% percent to 18% over the last ten years. To deal with the obesity epidemic, a number of technology interventions, including the use of robotics and virtual reality games, have arisen to motivate youth to become physically active. The difficulty though lies in providing a tool for health professionals to embed established clinical health protocols into these technologies. As such, in this paper we present a mixed reality system that translates physical demonstrations of various exercise protocols into movements for a robotic agent. This is accomplished by mapping real-time data from an RGB-D sensor to a robotic exercise coach. Details of the system are discussed and results from evaluation with 20 human subjects are provided.