Understanding the relationship between the demands of a sport, on the one hand, and an athlete's capacity and equipment, on the other hand, is vital for achieving optimal performance in sports. In cross-country skiing, equipment development has been driven by technological innovations as well as by changes in the competitive forms of the sport and improved course quality. However, given that the effects of equipment modifications may vary between specific parts of the competition, it is crucial to understand the importance of each aspect of the competition with respect to overall performance and the effects of changes in the equipment. Until now, the athlete`s perceived need for equipment adaptation has been an important driver of its evolution, while research has thus far had a somewhat limited role. A key part of equipment evolution in cross-country skiing came about when the new movement and skiing style of skating, known as the skating style, appeared toward the end of the 1980s. The skating style offered an increase in skiing speeds compared to the classical style, especially on flat and downhill terrain. Today, competitive cross-country skiing consists of both the classical style and the skating style. Each style contains an arsenal of subtechniques, the use of which depends on the efficiency of the technique at a given speed, incline, and snow conditions. The skating movement is dependent on hard-packed snow and a wide track. Since the athlete performs push-offs perpendicular to the ski, which remains gliding during the pushoff at a certain angle relative to the track, the skier moves forward in a zigzag-like fashion comparable to speed skating. In order for a skier to perform the skating technique optimally, the equipment has evolved considerably compared to the classic style. For example, the ankle stability of the boot has increased and longer poles are used. In general, the ski equipment must ensure that metabolic energy delivery is transmitted as efficiently and economically as possible into propulsion and speed along the track. This can be achieved through the implementation of new mechanisms that optimize power transmission or allow for greater power development through optimized muscle function. As an example, the increased efficiency and speed in speed-skating was achieved by replacing the conventional rigid connection between the boot and the skate blade with a hinge mechanism under the ball of the foot. The new hinge unconstrained ankle rotation while the skate blade remained flat on the ice, allowing for more work to be done by the muscles spanning the hip, knee and ankle. It is therefore not unlikely that a rigid ski boot and a hinge mechanism under the foot will be a good strategy for improving efficiency in cross-country skating-style skiing as well. At the same time, lower equipment weight and/or the ability to reduce air or snow friction may have an impact on performance because less power is required to maintain or increase speed. Often one wishes to minimize equipment weight in order to reduce metabolic cost, while any adaptation of the equipment meant to improve functionality may lead to increased weight. The quantitative relationship between the weight of ski and binding and its effect on technical aspects and metabolic cost is not well understood. Establishing knowledge of such a relationship is important for the development of future ski equipment. In this dissertation, these challenges have been addressed through three main studies and a pilot study by taking into account today's demands for competition and the effect of changes in equipment design on performance-related mechanisms. Study I compared speed and heart-rate profiles of world-class male and female skiers during international cross-country skiing competitions in both classical style and freestyle. The athletes performed two competitions in an individual start format, 15 km for men and 10 km for women. A GPS and heart-rate monitor tracked position, time and heart rate in uphill, flat, and downhill terrain. The average speed was ~10% higher during skating than classical style for both genders. The corresponding speed differences between freestyle and classical uphill and flat terrain differed significantly (12% and 8% for men, and 15% and 13% for women, respectively). The performance on uphill terrain had the strongest correlation to overall performance in both techniques and in both genders. Study II and the pilot study examined the effect of hinge positioning, with a newly developed skate binding with a mechanical hinge mechanism between the boot and the ski binding, and the effect on efficiency, cycle characteristics, and synergistic components of muscle activation in lower-limb muscles in uphill skating. Skiers used a custom-made boot and binding system that included an adjustable hinge-positioning system. Three hinge locations were tested while performing submaximal roller skating intervals in uphill on a treadmill. The hinge positioning did not affect metabolic cost, efficiency, or cycle rate, despite the fact that athletes preferred the middle hinge. However, systematic changes in muscle activation patterns associated with changes in hinge positioning were found. Study III examined the cost of increased weight of the equipment on efficiency and kinematics in moderate and steep uphill skating. Skiers used roller skis where the weight could be adjusted in order to understand the effect of distal loading on physiological and kinematic factors at four different distal loads. The distal loading was responsible for an average increase in metabolic rate and reduction in efficiency which was significant only in steep uphill skating. The biggest differences in performance between classical and skating, and between women and men were found in the uphill sections. This is also the terrain in which heart rate indicates the highest intensity and where the correlation to overall performance is strongest. By implementing a hinge mechanism in a skate-ski binding while uphill skating, there was no effect of hinge positioning on physiological responses or kinematics under submaximal loads, despite the fact that athletes experienced large differences between hinge positioning and that muscle activation patterns indicated different muscle activation patterns and force development patterns. Performance on snow also indicates individual and general preferences. The effect of increased distal load on metabolic rate and efficiency, however, was dependent on the steepness of the incline and technique, and increased distal load led to higher energy cost despite the fact that the kinematic patterns of the skiers remained approximately unchanged.
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