INTRODUCTION: Force production plays an important role in classical cross-country skiing. By using a special force plate System it is possible to measure both vertical and horizontal forces during diagonal skiing (e.g Komi & Norman 1987). The effects of waxing and ski properties are, however, difficult to estimate accurately as the force production even in experienced skier may vary considerably. The purpose of the present study was to construct a novel ski tester that would simulate the force production of natural skiing and allow accurate measurements in laboratory conditions. METHOD: An experienced male skier skied over a 6 m long force plate System with a velocity of 4 m/s. Vertical and horizontal forces were recorded and used as a reference data for a ski tester. A 13.7 m long ski tester using a 7.5 kW motor attached to a linear motor unit was equipped with pneumatic cylinder and 6 pieces of 1 m long force plates. A ski was attached to the cylinder and pressure against the force plates and the velocity of the ski were adjusted using LabWiev-program (National Instruments Corporation, USA). Once the force data of the tester matched the reference data, three different waxing conditions (slippery, medium grip and good grip) were tested. Measurements were made in the Vuokatti skiing tunnel with a constant temperature of - 5.8 degrees and air humidity of 78%. RESULTS: The force curves of the skier and ski tester were almost similar. Figure 2 shows an example of the horizontal forces. Large variations were observed in the produced forces by the skier although the skiing velocity was kept the same. However, the consecutive force curves produced by the ski tester with the same settings were almost identical. The effects of different grip wax conditions are seen in the figure 3. DISCUSSION: Controlled skiing conditions to examine the effects of skies and waxing together with forces and speed are often difficult to obtain. The present study Shows that even with experienced skier a certain amount of Variation takes place in the force production during repetitive cycles. The novel ski tester proved to be able to simulate the force production of natural skiing and the effects of different grip wax conditions on the ski forces were seen both during gliding and kicking phase. It is concluded that the new ski tester offers an excellent possibility for testing both skies (construction and base) and waxing in laboratory conditions.
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