We took an avid runner on a pretty leisurely ride with us awhile back. She is quite fit, runs 5+ days a week, spin classes, you know, one of those "active people." By mile 5 she was absolutely blown up. She said something along the lines of, "I don't know how you do this. This is torture."
Start him getting saddle time ASAP. Completely different muscles at work.
__________________
