One can postulate many theories related to the effects of good rhythm. Good rhythm is critical in good movement and is important to follow in training. Rhythms are also important in all aspects of life: biochemically, physiologically, and behaviorally. Abiding by these takes care of some very basic survival needs, opening the doors to improved human performance in all facets of life, especially athleticism.
I don't think it's a coincidence that societies that put a large emphasis on music and dance seem to evolve some very athletic individuals. Rhythm is highly emphasized in these societies.