My lower back hurts like a @%&^$#^ from mile 5 to any mile, beggining to end of the season, high or low gears.. Sometimes off the bike, in the office, it will kind of lock on me too.. Im 27. many injuries including bilateral shoulder dislocation.. back to the bike pain, I figure if I go really fast and get my adrenaline way up there, I don't feel the pain as much.