I want to continue the ski fitness series by moving on to the core muscles. As with most sports, core strength is important in skiing for stability and balance. Having a solid core will enable you to maintain a strong position even when the terrain is trying to throw you off balance. This is especially true in bumps, crud or slush - all the difficult, uneven conditions really.
The core muscles are the abs and back. Various exercises for these go in and out of fashion - sit-ups and crunches are less popular at the moment for example. The current popular exercises are things like the plank, or the many Swiss-ball exercises. Also good are press-up variations (e.g. clapping your hands during press ups).
As with the legs, free weights are good for a range of muscles. Again, squats are a great starting point, and should be included in any weights programme for skiing. In fact, some would say squats are about the only exercise you need.
It really is up to you to find what works - there are many approaches to developing core strength. However, it is not to be ignored if you want to maximise your performance. The next fitness post will move up the body again to the arms.