I'm about to move onto the interval portion of my training but I don't really know what to do. I understand intervals are hard efforts for some length of time followed by a recovery period and repeat. How long should my intervals start at? How many do I do? Should I focus on short bursts of power or sustained efforts? I am trying to be a climber and while I can stay seated and keep a good pace up a climb I have no explosiveness, i.e. I climb like jan ullrich, in the saddle no matter what if possible. Any tips?