A Comprehensive Comparison and Validation of Published Methods to Detect Turn Switch during Alpine Skiing

Abstract

The instant of turn switch (TS) in alpine skiing has been assessed with a variety of sensors and TS concepts. Despite many published methodologies, it is unclear which is best or how comparable they are. This study aimed to facilitate the process of choosing a TS method by evaluating the accuracy and precision of the methodologies previously used in literature and to assess the influence of the sensor type. Optoelectronic motion capture, inertial measurement units, pressure insoles, portable force plates, and electromyography signals were recorded during indoor treadmill skiing. All TS methodologies were replicated as stated in their respective publications. The method proposed by Supej assessed with optoelectronic motion capture was used as a comparison reference. TS time differences between the reference and each methodology were used to assess accuracy and precision. All the methods analyzed showed an accuracy within 0.25 s, and ten of them within 0.05 s. The precision ranged from ~0.10 s to ~0.60 s. The TS methodologies with the best performance (accuracy and precision) were Klous Video, Spörri PI (pressure insoles), Martinez CTD (connected boot), and Yamagiwa IMU (inertial measurement unit). In the future, the specific TS methodology should be chosen with respect to sensor selection, performance, and intended purpose.

Keywords: IMU; accuracy; force plate; motion capture; precision; pressure insole; sensor; ski.

Figure 1

Illustration of the experiment configuration in the indoor skiing carpet.

Figure 2

Graphical illustration and equations to clarify the interpretation of the data presented in the results timeline. i, participant index; n, number of participants per method; SD , standard deviation; CI_lower, lower confidence interval limit (percentile 2.5); CI_upper, upper confidence interval limit (percentile 97.5).

Figure 3

Timeline depicting the accuracy and precision of the turn switch detection methodology. The left side (a) figure shows the accuracy (black dot), standard deviation of the accuracy (whiskers) and precision (shaded area) of every method calculated with all turns pooled together. The right side (b) graph separates the data by turn size, long turns (red) and short turns (blue).