# Development of Equipment for Ski Mountaineering, a New Olympic Event
## 4 Ski Boots  
The major difference between the ski boots utilized in SkiMo and those used by alpine skiers is that the former are considerably lighter and designed so that the cuff can rotate around the ankle, allowing a switch to so-called \"walking mode\" and, at the same time, reducing the weight (Figure 1). Until minimum weight limits were set recently by the ISMF (Table 1), minimizing weight was the major challenge for manufacturers of SkiMo ski boots, and the relationship between the weight of a boot and the energy cost of skiing has been explored by a number of researchers [31; 32; 33]. [PERSON] reported a 2-3% increase in the energy cost when a 1 kg weight was attached to the ankle [25]. A more recent study on skiers moving at racing speed demonstrated that as little as 200 g of extra weight in the shoe increases the vertical energy cost by 3%, which can be detrimental to performance [34].  
The development of new composite materials (e.g., based on personal communication with boots manufacturers molding technopolymers (Girlamid) reinforced with carbon fiber or full carbon) has now made it relatively easy to design extremely light ski boots that adhere to the ISMF weight limits. Therefore, the constructive challenge has now shifted towards the reliability of the equipment under different environmental conditions and on different types of terrain. When combining materials with different characteristics, the major difficulty lies in exploiting the advantages of each individual material without compromising those of the others [35]. To maximize safety, the ISMF states that boots must be designed to be used with metal crampons (Figure 1), and the entire sole must be covered with rubber at least 4 mm thick and with at least 8 indentations under the heel and 15 under the front section. This rubber surface facilitates walking/running on sections where the skis are carried on the backpack.  
Another aspect to be taken into consideration is the ease with which the cuff moves with respect to the rest of the ski boot. Anecdotally, skiers prefer a boot with an extensive anteroposterior range of motion (\"high flexibility\") that allows a more efficient stride, both uphill and on flat terrain. On boots that are most admired, the cuff is connected to the remainder of the boot with ball bearings (instead of studs), which allows an extremely smooth and wide range of joint movement [36], while maintaining tight control of the supination and pronation of the feet. This is particularly important in the case of SkiMo because it makes it possible not only to climb directly up a maximal incline but also to ascend transversely in a zig-zag manner. When climbing transversely, the skis tend to follow the inclination of the slope, and the skier must exert pressure to avoid losing grip [37].  
Competitive alpine ski boots are considerably stiffer than the boots utilized in SkiMo, wherein later models have begun to look more and more like XC ski skis stating boots. However, the former are lighter and lack a locking mechanism, which in SkiMo is obtained by using a single buckle (a quick, one-motion system positioned on the back between the cuff and the heel) that at the same time tightens the upper cuff and locks the flexion-extension at the ankle joint.  
In summary, the varying mechanical properties of the different materials utilized, as well as their interactions, make SkiMo boots one of the most complex footwears used in winter sports. Future approaches, such as modeling, might improve the application of these properties and interactions to achieve even better reliability and safety [38].