Well, I just put myself in the bottom 20% because some days I can only ride about 5 miles (with a few short hills) before I have to turn back home, thanks to Chronic Fatigue. Very frustrating. Other days, I can ride 15-20 miles and it doesn't do me in, but I don't want to push it, or I'll be laid up too many days in a row afterward.
However, any day I can actually get on the bike and ride outdoors is an excellent day!