This year I have returned to alpine skiing and found myself relatively fit for quite intensive skiing session (up to 10 runs per hour for 3-4 hours straight twice a day for 5 days) except for two things where my body failed.
Second one: While I can do quick intensive turns without problem I've found that my legs haven't enough strength and endurance - I can't hold steady downhill body position for longer than a few seconds and when I do hockey stop from high speed my thighs hurt a lot.
I already do more than hundred body-weight squats a day twice a week and I need to find out how to increase load on my legs but preferably without additional equipment as I live in a very small apartment and can't afford to spend additional hour to go to a gym.
So far I've found that pistol squat is good to increase load but I have problem with my left knee and I probably won't be able to train both legs equally. Another one is wall sit but again, Wikipedia says that it is terrible exercise for someone with an existing knee problem. Any advice?