Ski Pole Summary
A ski pole's purpose is to increase an alpine skier's balance, speed and acceleration. However, in cross country skiing, they represent a significant form of thrust. AT skiers require telescoping poles that can react to the different types of terrain they are on. So how you will be using a pole definitely affects the type and length of pole that you will be needing.

When picking a pole, careful consideration must be given to how much you use poles (this determines whether or not a good pair of poles will be a good investment); what kind of materials you want to use (carbon fiber and aluminum are the most popular); and the type of grip on the pole (better grips are more comfortable, easier to grip and make for more accurate pole plants). Obviously, if you just use a pole for pushing yourself around on flats so you can get up to a lift, you don't need a high tech pole. For those of us that need a pole to do more then push us around, they are worth looking into.
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