INTRODUCTION: Measurements of performance and physiological characteristics in elite athletes need to be reliable and valid, in order to differentiate between meaningful changes, trends and inherent test variability [1]. However, reliability measures for cross-country ski specific test protocols involving various sub-techniques are currently lacking or remain unreported. This study aimed to investigate the test-retest reliability of a comprehensive cross-country ski specific test battery involving endurance, sprint and neuromuscular testing procedures. METHODS: Twenty-seven highly-trained cross-country skiers (17 male and 10 female, age: 22 ± 4 years, VO2max: 70.1 ± 4.5 and 58.8 ± 4.4 ml/kg/min, respectively) performed a test-retest protocol separated by two days in between. Performance testing consisted of a graded exercise test skating (GXT), a VO2max-test classic (VO2max-test), a 24-min double poling time-trial (24-min DP), a double poling peak velocity test (DP Vpeak), and a 1-min anaerobic capacity test skating (V2 1-min) all using roller skis on a treadmill. In addition, participants also performed a 20-s double poling peak power test on a ski ergometer (SkiErg DP) and explosive strength test for the upper body (UB-ST) on a custom-made device with light, medium and heavy load. Intra-class correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV) test statistics were calculated for all variables. RESULTS: Time to task failure performance in the GXT and VO2max-test, time-trial performance in 24-min DP and V2 1-min, as well as peak velocity in DP Vpeak all demonstrated excellent ICC (0.96 - 0.99) and CV (1.0 - 2.3%). Measured absolute VO2max during the ski specific treadmill test displayed excellent reliability (ICC: 0.99; CV: 1.4%; SEM: 62 mL/min). Relative peak power during the SkiErg DP showed excellent reliability (ICC: 0.99; SEM: 0.18 W/kg; CV: 2.4%), whereas reliability measures for relative upper-body peak power in the UB-ST were acceptable (ICC: 0.89 - 0.95; SEM: 0.59 - 0.91 W/kg; CV: 5.0 - 7.9%) across all loads. CONCLUSION: In highly-trained cross-country skiers, sport-specific aerobic and anaerobic performance tests on a treadmill using roller skis demonstrated high test-retest reliability, while neuromuscular performance measures for the upper body being somewhat less reliable. The current study provides comprehensive cross-country ski specific test-retest reliability measures for power and endurance based test protocols in various skiing sub-techniques. These findings allow athletes, coaches and scientists to accurately track performance changes between trials, which is a requirement in the elite athlete population with its small inherent performance variation.
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