Determinants of performance in male and female adolescent competitive cross-country skiers

Abstract

The process of adolescent cross-country (XC) skiers’ development to become elite senior XC skiers is multifaceted, and a complementary mix of athletic attributes has to be acquired and improved. This includes physiological attributes such as a high energy turnover and efficient movement economy; applying tactics in racing situations; and the ability to learn training methods, tactics and technique. Given the complex and demanding nature of XC skiing and the lack of research in adolescent XC skiers, a broad approach to explore the determinants of performance in male and female adolescent skiers is warranted. Such information may provide important insights for the development of performance in XC skiers.

This research project used laboratory tests (papers I-II) and a combination of laboratory tests with novel in-field experimental approaches (papers III-IV) to explore the determinants of XC skiing performance in male and female adolescent competitive XC skiers.

In papers I-II, we explored the physiological determinants of performance in male and female adolescent skiers (paper I) and sex differences in these determinants within adolescent (~15 yrs), junior (~18 yrs) and senior (~28 yrs) XC skiers (paper II). Gross efficiency (GE), peak oxygen consumption (V̇ O2peak) and accumulated oxygen deficit (ΣO2def) were calculated from treadmill roller ski skating. Upper- and lower-body maximal strength were also tested. On-snow performance (distance and sprint) for the adolescents in paper I was established from unofficial national championship results for this age group.

The sex differences in XC skiing performance ranged from ~15–25% in the lab-based performance tests and were similar between the different age groups. The different physiological determinants affected performance similarly in adolescent boys and girls. V̇O2peak seemed to be the most important physiological determinant in explaining sex differences in performance within all age groups, and the most important determinant for both laboratory and on-snow distance skiing in adolescent skiers. However, upper-body strength and body mass index seemed most important for on-snow sprint performance. Moreover, the complexity of on-snow skiing performance in adolescent skiers is highlighted, as V̇ O2peak, ΣO2def and GE explained ~80% of the variation in laboratory performance, but were substantially lower in explaining outdoor performance (~20-30% of the variation).

In paper III, we used a novel approach by combining laboratory measures with inertial measurement unit (IMU) and global navigation satellite system (GNSS) measures to describe pacing patterns and sub-technique selection during racing and compared these patterns to those of elite senior skiers. The skiers performed a free technique rollerski time trial (TT) over age-related racing distances using the GNSS/IMU system to track position and speed, and classify sub-techniques. Lab-based skiing economy and V̇ O2peak were used to calculate the relative oxygen demand (V̇ O2dem) in 13 undulating and uphill segments of the race.

The adolescent skiers tended to exhibit higher mean exercise intensity than older and more experienced skiers (120 vs. 112% of V̇ O2peak), with a more pronounced positive pacing pattern (130 vs. 110% of V̇ O2peak for the initial part of the race). Furthermore, the adolescents used more of the “low-speed sub-technique” Gear 2 (23 vs. 14%), less of the “high speed sub-technique” Gear 3 (36 vs. 45%) and had more frequent transitions between subtechniques (~18 vs. ~15 transitions·km-1) than the elite seniors. Hence, differences in physical ability affect speed and sub-technique selections, implying a need for differentiating technical training for different ages and levels.

Technical training for adolescent athletes most often happens in large groups with a high athlete-to-coach ratio, which restricts coaches’ opportunities to provide individual feedback. Thus, organizing practice sessions to facilitate more individual feedback could be an important aspect of technique training. Therefore, in paper IV, we investigated the effects of observational feedback in an applied setting using a novel approach with a long-duration learning intervention. The adolescent skiers were divided into a control group and three intervention groups (dyad practice, video or coaching feedback), which practiced the Gear 2 sub-technique 6x30 min in total over a 5-week period, on rollerskis outdoors. High-speed performance and skiing economy were assessed on a rollerski treadmill before and after the intervention.

The video and coaching feedback groups improved high-speed performance during the intervention (2.1% and 3.8%, video and coaching respectively) and coaching feedback improved performance more than dyad practice. Overall, our data suggest that feedback from a competent coach is better than observation for improving performance in adolescent athletes. However, self-observation through video with attentional cues is seen as a promising tool for increasing valuable individual feedback when coaching large groups.

Overall, this thesis shows that the physiological determinants of XC ski performance and the sex difference in these determinants are similar in adolescent skiers (14-15 yrs) and older skiers. Further, adolescent skiers seem to use these physiological determinants in a similar manner to seniors in a racing situation, although with a more pronounced positive pattern and more use of “slow-speed sub-techniques”. Finally, we show that a competent coach is important for technique learning, but self-observation through video is a promising tool.