So after getting my bike a few weeks ago and attempting some short rides i have finally admitted to myself that I am out of shape. I think college did this to me. I turned into a sloth and all i ate was junk food, now i'm paying for it. I used to be very active, i raced bmx every weeked, and rode every day and did a lot of rock climbing for strength training. When i first got the bike i was able to do 10-20 mile rides with no problem. the more i ride the less i'm able to accomplish. 3 miles in the park drained me today!!! when i get done riding the muscles in my legs feel like concrete (mostly my thighs, my calves dont really bother me). I want my energy back. i dont know where to start. any good books, recomendations?