Those speeds are indeed impressive. I'm riding more than ever, six times per week weather allowing, averaging 12 mph on a good day, and have had some fatigue issues. The key for me is to keep the time/ distance down. I'd rather ride 15 miles every day than longer rides with days off in between. If weather forces a day off, then I'm ready for a 20 plus ride the next day.
Whatever works for you at your current level of health and fitness; you can't fool mother nature!
