IN SEARCH OF GOOD PERFORMANCE INDICATORS FOR SPEED SKATING

The force produced to propel a body forward in speed skating is directed almost perpendicular to the forward motion, because a skate moves nearly frictionless in the for-aft direction and more or less fixed (against the ice) in sideways lateral direction, resulting in a sliding point to push off against. This unique propulsion property makes speed skating challenging to master, the movement is quite different from propulsion methods in daily life like walking and cycling, and challenges the biomechanical interpretation1. In the present study we are looking for performance indicators that will predict the quality of a stroke or of a section (curve or straight). In close cooperation with Dutch elite coaches some promising performance indicators have been selected for an initial examination. One of them is the time both skates make contact with the ice simultaneously, the so-called double stance phase (DS). It is hypothesized that a shorter DS phase can lead a more effective the push-off. The data collection is used to: 1. develop good algorithms to get the DS phase automatically, and 2. to verify empirically whether the hypothesis is true. Here we specifically focus on the DS phase in the curve. Six, of sixteen skaters of a regional junior team (age 17.8±1.4), on national level, were asked to wear IMU3 during their regular training twice a week. The IMU sensors are attached to both left and right skate. The DS phase both from Left to Right and Right to left vary between skaters: on average 346 ±83 306 ±80 ms. For most skaters, but not all, a relationship can be seen between the time it takes to round a curve (~ speed) and the time in DS a slower curve relates to a longer DS. Other factors like ice quality seem to have influence on the DS timing. The first performance indicator investigated shows clear differences between skaters. Results show a relation between the DS and curve speed, supporting our hypothesis. Other contributing factors will have to be investigated in more detail. Next step will be to use this parameter as Real-Time feedback and investigate whether it is possible to influence the skater's behavior with respect to the DS timing. The currently developed instrumented Klapskate2 will further broaden the possibilities to give feedback in real-time on the ice.[1] Houdijk H, de Koning JJ, de Groot G, Bobbert MF, Van Ingen Schenau GJ "Push-off mechanics in speed skating with conventional skates and klapskates" Med Sci Sports Exerc 32(3), p.635-641 (1999)[2] Kruk, van der E, Braver, den O, Schwab, A, Helm, van der F. & Veeger, D. "Wireless instrumented klapskates for long-track speed skating" Sports Engineering 19, p.273-281 (2016)[3]Shimmer3, ''Consensys User guide'' Available: http://www. shimmersensing.com.