I've got some interesting news to report, Coach.
I've been riding the mountain bike pretty hard since July. Somewhere around last October it felt like my legs were burned out and I just couldn't recover from my workouts (even after a rest of 5 days). So I started running again (didn't want to run with all the extra weight at first). Up until last week, I laid off the biking for a good two months.
The weather has been real warm lately, in the 50's and 60's, so I figured why not? I took the bike out last week and my legs felt amazingly fresh. In fact, I felt like an animal out there. I had power and endurance like I haven't had since I started getting back into exercise hard core.
Yet, I couldn't break a personal best I set in the fall. Going from point A to point B on the bike, on a dirt trail, in 32 minutes was my PB (in July the number was 45 minutes). I biked 3 times in the last week, all of them coming in at 32-33 minutes for this clocked part of my 1.5 hour ride. I was getting seriously concerned thinking here I feel great, but WHEN if ever would I break the 30 minute mark?
Well, yesterday I pushed it, and didn't even overdo it. And I came in at 29 minutes flat, shattering my old PB by 3 minutes!
Moral of the story for me? When your legs burn out doing one exercise, lay off that exercise for a month or two but continue working cardio doing something different.