Differences in V1 and V2 ski skating techniques described by accelerometers

Abstract

The aims of the study were to describe the differences between the ski skating techniques V1 and V2 and evaluate reproducibility in complex cyclic hip movements measured by accelerometers. Fourteen elite senior male cross-country skiers rollerskied twice for 1 min (V1 and V2) at 4° inclination and 3 m/s. Tests were repeated after 20 min and again 4 months later. Five triaxial accelerometers were attached to the subject's hip (os sacrum), poles, and ski boots. Post-processing included transforming to an approximately global coordinate system, normalization for cycle time, double integration for displacement, and revealing temporal patterns. Different acceleration patterns between techniques and large correlation coefficients (Pearson's r = 0.6-0.9) between repeated trials were seen for most parameters. In V2, the hip was lowered [-10.9 (1.2) cm], whereas in V1, the hip was elevated [4.8 (1.5) cm] during the pole thrust. In conclusion, V2 but not V1 showed similarities to double poling in the way that potential energy is gained between poling strokes and transferred to propulsion during the poling action. Elite skiers reproduce their own individual patterns. One triaxial accelerometer on the lower back can distinguish techniques and might be useful in field research as well as in providing individual feedback on daily technique training.

Three-dimensional Force and Kinematic Interactions in V1 Skating at High Speeds

“…The cycle rate of 0.88-1.06 Hz and cycle length of 4.10-4.25 m observed here are quite similar to previous findings on the VI technique, both on snow and using roller skis (4,17,21,25,31,32,38). At the same time, the cycle rate here was approximately 18% lower than the 1.3 Hz recorded during maximal speed trials at an incline of 7°-10° on snow by Stoggl et al (35).…”

Technique analysis in elite athletes using principal component analysis

“…Therefore, we will briefly discuss the biomechanical plausibility of whether the observed technique features may relate to the efficacy in propulsive energy production: The first aspect appeared as timing differences in pm 2 and pm 3 , which captured a combination of hip flexion and aspects of the pole push and quantified the sagittal arm swing and a symmetric hip ab-/ adduction, respectively. We speculate that the better ranked athletes utilised potential energy more effectively in the pole push (Losnegard et al, in press;Myklebust, Losnegard, & Hallen, 2014), by coordinating their movements such that major muscle Figure 4. Hybrid movement pattern (Equation 5) from the average movement of the three lowest ranked skiers, where 4 was replaced with the mean of the three best ranked skiers (black lines).…”

Embedded inertial measurement unit reveals pole lean angle for cross-country skiing

“…Given the known distance between the two markers (950 mm), the expected resolution of the lean angle measured in the vertical plane from the video images is arctan(2/950)=0.12 • . The procedure utilized here was similar to that described in [19].…”

“…While IMUs have been deployed to study skiing technique [18][19][20][21], they have not been used to study the motion of the pole beyond detecting pole-terrain contact events, cycle duration, cycle speed, and cycle length [19,22]. Nevertheless, a pole-embedded IMU also provides the requisite data (acceleration and angular velocity) needed to estimate the lean angle of the pole as well.…”