Thank you for your comments. My client is training for a marathon outside of my training with her. I do completely understand that running is the best way for training for a marathon, this is her 4th. I have train for half marathons before. However she just asked me this question, and I didn’t know where to find the a real answer instead of doing the same thing she did, Goggling it. Karin, Thank you, I will do that and forward the information to her. Thanks again Karin, Paul, and Harris.