Last Saturday I bicycled for 15 miles, walked 5 miles around the school track, then rode the bike 5 more miles on the way home. That was a total of 25 miles under "Ken" power. I don't know that I've ever done that distance in a day - even when I was a teenager riding my bike most everyday. I was in my MAF zone most of the time for the entire workout. The walk was well into the overall workout. Just walking had my HR planted in the 115 to 120 range. Sunday was a recovery day. My legs were tired and ready for a day off.