On certain climbs, particularly Himalayan climbs and big wall climbs (cliffs that require multiple days to ascend), climbers will ascend a fixed rope instead of ascend the snow or rock, for both speed and convenience. Sometimes, climbers will get stuck on a rappel during a climb and need to improvise by climbing the rope. Ascending the rope requires a pair of ascenders and a set of aiders, or a friction knot, and is usefully referred to as "jugging" the rope.
Using Ascenders on Moderate Terrain
Ascenders come in a pair, one for the left hand and one for the right, and clip onto a rope. Popular models include Jumars and the Petzl Ascension. Some, such as the Petzl, are better for climbing ice and snow-encrusted ropes than others.
On moderate slopes, ascenders are used as an aid while walking up a slope. Usually, you only use one ascender attached to the rope, instead of using two, in part to save weight. Take a daisy chain and clip one end to your ascender and the other end to your climbing harness, shortening it so that the daisy chain is as long as your arm's reach. Clip the ascender on the rope, slide it up the rope to arm's length so that the daisy is tight against your body, and walk up. If you need a rest, simply stand straight and allow the ascender on the rope to take your weight.
Using Ascenders on Vertical Terrain
On vertical cliffs and overhangs, jugging requires two ascenders with daisy chains clipped to a harness and a pair of aiders clipped to one ascender. Aiders are four- or five-step ladders made of webbing, designed specifically for aid climbing. Clip the daisy chain to your harness and to each ladder, adjusting the length so it is at arm's length. Clip both ascenders to the rope. Stand up in the aiders, then slide the top ascender (which doesn't have the aiders) up to arm's length. Hand your weight off this ascender, then slide the bottom ascender (with the aiders) up to just below the top ascender and stand up in the aiders. This technique uses the legs, rather than the arms, to take your weight.
In a pinch, friction knots, such as Prusik knots or a piece of webbing tied with a kleimheist knot, can be used in place of ascenders. This is often used by glacier climbers who don't want to carry the weight of ascenders but may need to ascend the rope in the event they fall into a crevasse. Prusik knots can be used with Prusik loops, loops of smaller, thinner rope that are about 2 feet in length. Practice tying Prusik knots before using them. With practice, they can be tied on the climbing rope with one hand. A kleimheist should only be used with regular webbing, not Spectra webbing or Spectra cord, as Spectra can melt under the friction applied by the knot.