A Long-Term Study of Aerobic Performance in Elite Cross-Country Skiers: How Age and Sex Influence Career Development

Introduction Elite cross-country (XC) skiers undergo standardized testing to monitor their performance development and to calibrate training prescriptions. However, the long-term progression of performance indicators, such as maximal oxygen uptake (VO2max), performance at the second lactate threshold (LT2), and time-trial performance over an athlete's career remains unclear. This study aimed to investigate the longitudinal data from > 15 years of exercise testing with the Swiss XC ski national team to examine the trajectories of key performance indicators across the careers of male and female skiers. Methods The longitudinal development of VO2max, LT2, and 24-minute double poling performance (24-min DP), described in further detail elsewhere (Bucher et al., 2023), was analyzed in 72 male and 49 female current and former Swiss XC-ski national team athletes. The performance trajectories were modeled using mixed-effects approaches, with a linear random intercept for VO2max, a linear random slope for LT2, and a third-degree polynomial for 24-min DP. Fixed effects included age, sex, and their interaction, with random effects at the individual level. The study included 357 observations (n = 27 females, 48 males) for VO2max, 911 (n = 46 females, 65 males) for LT2, and 601 (n = 49 females, 70 males) for 24-min DP. Results VO2max in females tended to increase by 0.16 mL/kg/min per year (p=0.085), with no increase in males (0.03 ml/kg/min, p=0.627). Males had a higher baseline VO2max at age 18 (70.8 vs. 58.2 mL/kg/min, 21.6% difference), but the rate of change with age was not significantly different between the sexes (p=0.259). LT2 improved significantly with age for both sexes: females gained 0.038 W/kg per year (p<0.001) and males 0.052 W/kg per year (p<0.001). At age 18, males had a 23.2% higher baseline LT2 (3.34 vs. 2.71 W/kg). In the 24-min DP test, both sexes initially improved significantly (p<0.001). However, there was a notable decrease in the rate of improvement in males, as indicated by the quadratic age term (p<0.001). On the other hand, females showed a consistent linear performance trajectory throughout their careers, with no significant quadratic age term (p=0.430). Female skiers showed a baseline performance of 3820 m at age 18, while this value was at 4788 m in males, with males outperforming females by 968 m (25.3%). Discussion/Conclusion VO₂max, LT2, and 24-min DP showed distinct developmental trajectories across age and sex in elite XC skiers. While VO₂max remained unchanged, LT2 continuously increased throughout their career. On the other hand, 24-min DP followed a non-linear progression in males, with a slowdown in performance improvement as they transitioned from the U23 to the senior age category. These results highlight the importance of high initial VO₂max at the junior level and the greater trainability of LT2 and aerobic time-trial performance with the accumulation of specific training as athletes progress in their careers. References Bucher, E., Millet, G. P., Wehrlin, J. P., & Steiner, T. (2023). Test-retest reliability of ski-specific aerobic, sprint, and neuromuscular performance tests in highly trained cross-country skiers. Scandinavian Journal of Medicine and Science in Sports, 33, 2482–2498. https://doi.org/10.1111/sms.14473