INTRODUCTION: Several methods could measure the forces from ski or roller skis in cross-country skiing (Othonen et al., 2013; Hoset et al., 2014). Equipment which could measure medio-lateral forces may be of good help for investigating the relevant skating techniques. The aim of this study was to validate a pair of newly designed 2-dimensional force measurement roller skis. The vertical and medio-lateral forces which were perpendicular to the body of the roller ski could be measured. METHODS: Custom-made aluminium alloy frame of roller ski has been designed using finite element method (FEM). Static (10-150 kg) and dynamic (simulated skate skiing push-off jump) situation for the measurement roller ski was performed to reveal the validity of the system. 3D force plates (AMTI, Watertown, USA) were used, and the forces measured by the force plate were the reference. Three passive reflective markers and a 4-camera Vicon (Vicon, Oxford, UK) system were used to record the position of the roller ski in the global coordinate system. Forces were resolved into the global coordinate system and compared with the force components measured by the force plate. To demonstrate whether the force measurement roller ski would affect the roller skiing performance on the treadmill, a maximum speed test with V2 technique was performed using both normal and force measurement roller skis. RESULTS: The force-time curves obtained by these two different force measurement systems during dynamic situations were shown to have high similarity (coefficient of multiple correlation > 0.940). The absolute difference for the forces in X and Z directions over one simulated skate skiing push-off cycle was 3.9-33.3 N. When skiing on the treadmill, the durations for the tests did not have any major differences with different roller skis. DISCUSSION/CONCLUSION: FEM is a practical method to find the optimal shape as well as dimensions of a custom-made roller ski body and to determine the optimal location of the strain gauges in the roller ski body. This developed instrumentation, where the resistance strain gauges were attached to the suspensions of the roller ski wheels, is a practicable tool for measuring the magnitude of the forces applied on the roller skis in two dimensions in skate skiing. REFERENCES: Ohtonen, O. et al., 2013. Sports Eng Hoset, M. et al., 2014. Sports Eng
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