Today, science and technology play an ever-increasing role in top-level sports. Of special importance is to measure the performance of athletes during sports training and execution. To help our top skiers, we have developed a skating style two-dimensional force measurement roller ski.
For most skiers, roller skiing is one primary form of training method during the dry land training season, and it can be used to reveal skiing technique in more detail. VTT MIKES have developed a pair of roller skis for the measurement of vertical and medio-lateral forces generated by the skier. The development included modelling and simulation of the stresses on the roller ski frame, frame manufacturing, strain gauge instrumentation and calibration. The design specifications for the sensor were nominal force in vertical direction 1400 N and nominal force in medio-lateral direction 400 N. Skiability and weight of the designed sensor were also a significant design criterion.
The two-dimensional force measurement roller skis were designed and build by VTT MIKES. A custom-made aluminium alloy frame of the roller ski was designed using the finite element method (FEM). Finite element analysis (FEA) was used for dimensioning and determining the location of strain gauges on the ski frame. Both roller skis were equipped with four full-bridge strain gauge configurations (Figures 1) two for vertical forces (front and rear) and the two for medio-lateral forces (front and rear). The force measurement roller ski weighted 1358 g which was 333 g more than the state-of-the-art roller ski (1025 g) that acted as reference ski in measurements.
Thorough validation of the 2D force measurement roller skis were carried out. In first phase, the force measurement roller skis were calibrated in force standard machine by VTT MIKES in Kajaani. For vertical forces from 0 N to 1000 N and medio-lateral forces from 0 N to 400 N. In second phase, static tests were carried out on two force plates (Figure 2) that measured the forces in three directions. A roller ski was placed with one wheel on each force plate and loads from 0 kg to 150 kg were placed on the roller ski. To test the force measurement roller ski in a dynamic situation, a simulated skating push-off jump test was performed over one force plate by two (a male and a female) highly skilled skier. Finally, practical tests were conducted on a treadmill by the two skiers using the force measurement roller skis and the reference (state-of-the-art commercial) roller skis to find out if the extra weight of the force measurement roller skis affects skiing performance. This second phase testing was carried out by University of Jyväskylä in Vuokatti.
The tests carried out showed that the developed instrumentation is a practicable tool for measuring the magnitude of the forces applied on the roller skis in two dimensions. Moreover, the extra weight of the force measurement roller ski had only a small effect on adult skier’s roller skiing performance. Therefore, the newly designed two-dimensional force measurement roller skis are useful for future research during daily training.
More information can be found in the recently published in article:
S. Zhao, V. Linnamo, K. Ruotsalainen, S. Lindinger, T. Kananen, P. Koponen and O. Ohtonen, ”Validation of 2D Force Measurement Roller Ski and Practical Application”, Sensors 2022, 22(24), 9856.