Inertial measurement units (IMU) are implemented in a variety of commonly-used technological equipment including cars and smartphones. IMUs are small and sensitive to motion. Hence, IMUs have been introduced as a tool for technique analysis in several sports. Cross-country ski skating is a complex movement where both arms and legs produce propulsive forces. Hence, skiers have a large number of degree of freedom to optimize their technique to a variety of terrains. , and large individual variations are seen even between elite athletes. Because of the complexity of sub-techniques, individual variation between skiers, and small essential differences in timing of movements, it is challenging to determine what “good technique” looks like.
Place: Norges Idrettshøgskole
Accelerometers in cross-country skiing – a tool for technique analysis
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.