I'm not sure why anyone would use ma huang on it's own for one, but specifically in conjunction with exercise. Except with extremely good reasoning ma huang should not be used long-term and certainly not to enhance exercise. Further, vigorous physical activity (more specifically excessive sweating) weakens both the yin and the qi - it does not by default build the yin certainly - while it may generate physical strength (which depending on the terminology you are using is different from "internal" strength as it would be use in the context of tai chi theory for example).
I would suggest you more deeply consider what category ma huang falls in - "herbs that release the exterior wind-cold". It is not a stimulate per se, but is unfortunately abused as such when it is used out of the context of Chinese Medicine.