I've been in condition for these things in the past, but over a winter of mostly just walking, light cycling and gym climbing my legs and cardio had suffered.

I've been in condition for these things in the past, but over a winter of mostly just walking, light cycling and gym climbing my legs and cardio had suffered. It's explosive training, my muscles hurt afterwards, and I needed 3 days to recover. Over the month of stair sprinting every 3 days I regained about 5 pounds of(what I presume is) leg muscle. The premise behind it is that the high intensity stress of my short sprint sessions is effective way to prepare myself for the all day but lower intensity stresses of big climbs with big approaches, for my heart as well as my legs. My calves and achilles tendon took a beating on the trip, one thing I wasn't well prepared for was all the standing on my toes. I've relied on a period of sprints, either on stairs, flat ground or on a bike, to whip myself into condition a half dozen times over the past couple decades. At 46 I find I don't snap into fitness as quickly as I once did. And I don't live anywhere near big hills, if I did I would train on them more, but not at the full expense of running sprints.