Swim style evaluation from body worn sensors

Type: Semester thesis
Students: Urban Suppiger
Advisor: Marc Bächlin, Kilian Förster

The purpose of this thesis was to investigate, whether it is possible to evaluate a swimmer's swim style by recording data with body worn sensors. Two issues were chosen to be examined in detail, namely body balance and body rotation. 3-axial accelerometers were chosen as sensors and two of them were placed on the swimmer's body at the upper back and at the lower back.

During a pre-experiment, the recordings of the sensor system were compared to video recording data. The sensors were able to measure the body balance angle with an average error of only 2.4° and a standard deviation of 1.82° compared to the video data.

For the main experiment, 12 swimmers of varying skills swam different well-defined crawl exercises. The purpose of the main experiment was to evaluate how well the algorithm can classify the crawl exercises by measuring body balance and body rotation. In addition, the swimmers’ performance among each other was compared. Therefore, the swimmers were classified into three groups: competitive swimmers, recreational swimmers and occasional swimmers.

The exercises concerning the body balance were detected correctly in every case, whereas the algorithm properly classified 89% of the body rotation exercises. The comparison between professional and occasional swimmers showed interesting differences in body rotation parameters, which could hardly be measured without body worn sensors. Figure 1 shows one example of the body rotation of a recreational swimmer and figure 2 shows one example of the body rotation of a competitive swimmer. Better swimmers swim with a bigger amount of body rotation compared to recreational swimmer, while they achieved to rotate shoulders and hips more synchronously - at the same time and with the same amplitude.