In his doctoral thesis, Håvard Myklebust demonstrated how to capture skiers' technique outside of the laboratory.
"Placing small lightweight inertial measurement units, or sensors, on the skiers' body, boots, poles and skis allowed us to measure technical variables during training sessions. Technical variables which are difficult to detect and are related to performance," says Myklebust. The method could prove to be a valuable tool as it could be used outdoors on the snow, and provide better test data.
The doctoral thesis, Quantification of movement patterns in cross-country skiing using inertial measurement units, covers the validity of the method, its findings and how coaches and skiers can implement IMUs in their training. A total of 28 skiers were involved in recording data, some for as long as a year. Measurements included both on-snow skiing and roller skiing.
Capturing movement patterns
The cross-country skating technique is made up of complex movement patterns, with many variations. The IMUs measure the scope and duration of these actions. Timing is extremely important in such a technically demanding sport as cross-country skiing. Timing and movement patterns can be used to determine the skiers' balance, another important technique factor.
The movement patterns differ according to skiing technique. The V2 technique employs one synchronous double-poling action with each ski push-off, whereas the V1 technique sees one double-poling action with every other ski push-off. The sensors allow us to identify which technique is being used, regardless of individual variations. Intra-individual variations are significantly smaller.
"Repeated measurements over time provide us with data that can be compared to performance variations. In this manner, we are able to identify what would be the optimal technique for every skier," says Myklebust.
There is considerable variation between skiers but he found some general tendencies. Increased cycle length and lowered cycle frequency would lead to improved performance. Cycle length is the distance travelled on one ski between pole-plants (cf. illustration). Improved balance is required to extend the glide phase on one ski. Previous studies have found higher-ranked skiers to use a longer cycle length, but this study is the first to demonstrate the correlation between cycle length and individual performance. Elite skiers displayed better coordination of movements with longer glide length, less fatigue and improved performance (cf. illustration).
Technique differences between on-snow skiing and roller skiing
There are significant differences between on-snow skiing and roller skiing. Using the V2 technique uphill resulted in different hip rotation, greater lateral displacement, longer poling times and more fluid movements on snow compared to roller skiing. These findings should be used to close the gap between the two techniques.
"We can make roller skiing more similar to on-snow skiing by adjusting the skis and bindings," says Myklebust.
The sensors could be used by coaches and skiers during training. According to Myklebust, we should develop systems to compare the athletes' movement patterns to their optimal technique. This would allow the skiers to make adjustments on the spot and improve their technique in less time.