Development of Skill Scoring System for Ski and Snowboard

Abstract

Observation of dynamic posture during sports activity is one of the most important factors to give absolute evaluation to the player’s performance. The sports like the figure skating and the skiing have difficulty in evaluation of skill because the evaluation depends mostly on the observation from the third person. The training method for such sports inevitably needs feedback comments from the experts. However, it is hard for all players of the sports to receive such expensive feedbacks at any time when they need. In order to overcome the inconvenience to perform self-training without the third experts, this paper focuses on development of a training system using smartphone device that gives a clear guide for body balance control in the skier and the snowboarder. The system gives scores and comments for the ski’s parallel turn. The system automatically scores skill for body balance control regarding three aspects: the tempo at turns of body balance movements between the right and the left in the skiing, the distribution of body balance, and the angle between the snow slope and the body of the skier. This paper also performs a preliminary evaluation of the system in the case of snowboard. The system brings a new method to know the skills of body balance control in skiing and snowboarding from the absolute data measured by sensor devices.

Appendix

The approximation line for the balance angle is calculated using the least squares method. For any accelerometer data of X and Y axis represented by ($x_i$, $y_i$) where i is $0\le i<N$, we calculate a that makes minimal of;

$$\begin{aligned} S(a)=\sum (y-ax)^2 \end{aligned}$$

Because $S'(a)=0$,

$$\begin{aligned} \sum ~xy-a\sum ~x^2=0 \end{aligned}$$

$$\begin{aligned} a=\frac{\sum ~xy}{\sum ~x^2} \end{aligned}$$

The scoring equation for the balance angle uses the data in the right side to calculate $a_R$ and the one of the left side to calculate the $a_L$. The calculation for the score uses the absolute values of $a_R$ and $a_L$.