Purpose We examined the test-retest reliability of rollerski testing across a familiarization trial followed by three separate test trials (T1-T3) conducted within a 14-day period. Methods Ten competitive cross-country skiers performed three sub-maximal tests (5%, speed range 10-16 km h-1) and a maximal speed test until failure (MTF; ~ 5-8 min, 7%, > 10 km h-1) on a rollerski treadmill using the Gear 3 ski skating sub-technique. Reliability was assessed as within-subject typical error, expressed as a coefficient of variation (CV%, [confidence limits]) intraclass correlation (ICC, [confidence limits]), and changes in mean (%). Results The speed at MTF demonstrated a mean CV (T1-T3) of 1.5% [1.1, 2.6] and an ICC of 0.96 [0.87, 0.99], but a systematic familiarization bias from T1 to T2 (1.2% [0.1, 2.3]) and T2 to T3 (2.2% [0.1, 4.3]). Peak oxygen uptake exhibited a mean CV of 2.2% [1.6, 3.8] and an ICC of 0.93 [0.78, 0.98], with no systematic changes from T1 to T2 (- 0.2% [- 2.0, 1.6]) and T2 to T3 (1.8% [- 1.1, 4.7]). VO2 at submaximal load showed a mean CV of 2.1% [1.5, 3.3] and an ICC of 0.94 [0.84,0.99], with no systematic changes from T1 to T2 (- 0.7% [- 2.4, 1.1]) and T2 to T3 (- 0.1% [- 2.4, 2.3]). Conclusion The relatively low CV and high ICC for most measures suggest a high degree of test-retest reliability. However, the systematic mean changes in MTF indicate that familiarization trials are essential to provide valuable information about individual changes. Overall, these reliability measures can be used as a framework by practitioners to discern true changes when testing on a rollerski treadmill. Correction: European Journal of Applied Physiology https://doi.org/10.1007/s00421-025-05746-w
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