The classic cross-country skiing style is often used on prepared trails (pistes) that have pairs of parallel grooves (tracks) cut into the snow. It is also the most usual technique where no tracks have been prepared. With this technique, each ski is pushed forward from the other stationary ski in a striding and gliding motion, alternating foot to foot. With the “diagonal stride” variant the poles are planted alternately on the opposite side of the forward-striding foot; with the “kick-double-pole” variant the poles are planted simultaneously with every other stride. At times, especially with gentle descents, double poling is the sole means of propulsion. On uphill terrain, techniques include the “side step” for steep slopes, moving the skis perpendicular to the fall line, the “herringbone” for moderate slopes, where the skier takes alternating steps with the skis splayed outwards, and, for gentle slopes, the skier uses the diagonal technique with shorter strides and greater arm force on the poles (Wikipedia).
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