# Development of Equipment for Ski Mountaineering, a New Olympic Event
## 3 Skins  
To avoid slipping backward when skiing uphill, adhesive skins with combed hairs that grip the snow are applied to the base of SkiMo skis prior to an uphill section and then quickly removed in special transition areas before the subsequent descent (Figure 1). In this way, skins fulfill the same function as grip wax in connection with the diagonal stride technique in cross-country skiing, although skins provide even better grip and can, of course, be removed for skiing downhill. In the case of classical XC skiing, the interaction of the grip wax with the snow is influenced by the bending of the ski camber, which is, in turn, influenced by the load applied to the skis. Accordingly, the friction provided by the grip wax varies during the different phases of XC skiing, being higher during the kick and lower during the gliding phase [18; 27; 28]. Similarly, in SkiMo, the orientation of the hairs of the skins prevents the skis from slipping backward during the leg push while allowing forward motion during the gliding phase [29]. [PERSON] and colleagues [30] pulled a sled equipped with 12 different types of skins for 4 m at a constant speed of 0.36 ms\({}^{-1}\) and observed coefficients of gliding friction ranging from 0.22 for racing skins to 0.34 for those used in ski touring. Moreover, the coefficients of friction for these different skins varied in different ways with temperature. These gliding friction coefficients were 10-fold higher than that typical for XC skis [16] but only 10% of the grip friction when an apparatus was pulled with slowly increasing force in the grip direction of the skin. Typically, SkiMo skiers utilize three or four different types of skins for different snow conditions (e.g., artificial versus fresh/new snow), many of which require some initial usage before obtaining their optimal glide and grip characteristics. In connection to certain teams and individual events, the ISMF regulations [12] allow the jury to request athletes to bring additional pairs of skins. The difference between the gliding friction coefficient of XC skis and the grip friction of skins encourages technological developments that improve gliding via the latter while still maintaining adequate grip. The different attempts to reduce the friction of the skins utilized in SkiMo range from the usage of alternative materials (e.g., silicon rubbers) to skins that provide less grip and better glide specifically at the front of the skis, but these solutions have not yet been widely adopted by skiers themselves. While the ISMF rules [12] state that these skins must cover at least 40% of the length of the contact between the skis and snow (Table 1), skiers usually attach a skin to the tip of a ski with a hook and extend it over the rear binding, which covers considerably more than 40%. In addition to its length, the extent of grip provided by a skin depends on the material from which it is made (e.g., mohair and/or nylon), the characteristics of the hairs (thickness, density, length, and inclination), and environmental conditions (temperature and humidity of the snow and air, as well as other characteristics of the snow). Based on our interviews with the coaches and ski technicians associated with national SkiMo teams, another area that requires development involves the glues that adhere skins to skis. These must be strong enough to keep the skins in place during ascent and, at the same time, allow easy removal prior to descent. During a race, transitions must be as rapid and effective as possible, even when the skin and/or ski base are wet and/or snowy/frozen. To improve the balance between grip and glide even further, skins are also often waxed with a paraffin block containing compounds rich in fluorine in combination with liquid waxes that reduce the absorption of water, which could otherwise freeze under the skis. When athletes are required to climb snow corridors or cross ridges with their skis attached to their backpacks, crampons, i.e., metal (usually aluminum) claw-like structures placed under their boots, may be used.