Insole pressure measurement in speed skating

Ice speed skating is a difficult sport to master. Knowledge of his skating stroke can help a speed skater to improve his performance. A project has been started to create the ‘smart skate’ as a way to measure and give feedback about the technique of a speed skater. Currently an instrumented skate is used to measure stroke force, steering angle and lean angle of a skating stroke. Because this design is quite cumbersome, expensive and not universally applicable, it is unpractical. For this study, the assignment was to find other ways to measure stroke force and counter these drawbacks. The specifics of long track speed skating, like environmental conditions, acting forces and footwear have been examined. Together with the data to be measured, a list of requirements for force measurement in speed skating was completed. The research was focused on pressure sensitive insoles that can be placed inside the shoes as these have been proven to work in other sports like skiing and running. With time for this project being limited, only commercially available pressure insole systems were looked at. A long list of different systems was gathered and scrutinized, resulting in the selection of three candidates. Two of them were found to be too expensive, so the system of choice became the OpenGo insole system by Moticon. The Moticon insole system consists of 13 capacitive pressure sensors, a three-axis accelerometer and temperature sensor. Together with a coin cell battery, all this hardware is fitted into an insole with a thickness of just over 3 mm, creating a very compact package. For speed skating purposes, a set of custom sized insoles was ordered. The insole system was tested simultaneously with the current instrumented skate. By using the instrumented skate as ‘golden standard’, the accuracy of the Moticon insoles was to be found. Two 5-lap test runs were conducted at an indoor ice rink. Test sample size was later reduced as only one run provided good data for analysis. For left/right sides, an average force offset of 13% and 32% was found with a precision of 10% and 7% respectively. For peak forces, an offset was found of 10% and 32% with a precision of 15% and 10% respectively. Accuracy does not seem to be very good but sample size was only limited, insole coverage by pressure sensors is just 50-60% and accuracy of the instrumented skates is still under discussion. Further testing will need to be done to get better results from the insole system. The insoles do however seem to be a good addition to the current instrumented skate as they provide a user-friendly package for measuring force in speed skating and are able to show plantar foot pressure distribution, which can be of importance for improving speed skating performance.