Purpose
This project’s aim was to evaluate how, and to what extent, IMU-sensors can be used for technique analysis in cross-country skiing.
Project description
Up to 60 skiers will participate in this project. Movement patterns from sensors attached at their hip, skis and poles will be analyzed. First we aim at validating the accuracy of the sensors (compared to a 3D full body method). Secondly, we aim at identifying key features separating techniques, skiers and roller skiing inside on a treadmill, outside on asphalt and skiing on snow. We will also see how technique changes during a season and how these changes correlate to performance.
Results
A PhD-thesis is prepared based on the results presented in four articles, of which the first two focus on the reproducibility and validity of the IMU method, while the other two are more applicable to skiers and coaches. The main findings were:
- Using IMUs allowed for easy data collection, and revealed highly detailed and reproducible movement patterns.
- The accuracy and precision of measurements increased when accelerometer (accelerations) and gyroscope (angular rate) data were combined, and sideways center-of-mass displacement was accurately estimated by hip displacement.
- Limb-mounted IMUs provided a precise and simple way to perform ground-contact temporal analyses, except for estimating the timing of ski plants.
- Hip movement patterns in V2, but not in V1, showed a similarity to double poling in terms of hip lowering during poling. This allows potential energy gained prior to the poling thrust to be transferred to propulsion through the arms and poles.
- IMU data quantified essential V2 technique alterations affecting work economy and performance in elite skiers. Small likely effects on performance were found for both cycle time (more precisely poling time and pure glide time) and vertical acceleration. This novel finding indicate the importance of improved balance even for elite skiers.
- When directly comparing on-snow skiing and roller skiing, altered hip rotation patterns, greater lateral displacement, longer poling times, and a tendency to smoother hip movements were found for on-snow skiing.