Author(s): BUCHER, E., WEHRLIN, J.P., MILLET, G.P., STEINER, T., Institution: SWISS FEDERAL INSTITUTE OF SPORT, Country: SWITZERLAND, Abstract-ID: 2292

INTRODUCTION:
Performance development in elite cross-country skiing is primarily shaped during the general and specific preparation phases. However, limited evidence exists on which physiological and performance indicators change consistently from spring to fall, with only one previous study conducted in male skiers and restricted to a single season (Losnegard et al., 2013). This study quantified spring-to-fall changes in laboratory-based performance indicators in Swiss elite cross-country skiers over a 15-year period.
METHODS:
Retrospective longitudinal data from 81 male and 57 female Swiss elite cross-country skiers were analyzed across multiple seasons. Same-year spring-to-fall assessment pairs (spring: May–June; fall: September–October) were constructed for body fat percentage (BF%), fat-free mass (FFM), relative hemoglobin mass (HbM), relative VO₂max, relative power output at the second lactate threshold (LT₂), gross efficiency (GE), and squat jump peak power (SJ), yielding 1551 paired observations. Spring-to-fall changes were calculated as paired differences (fall − spring) and mean-based relative changes (%Δ). Statistical certainty was evaluated using linear mixed-effects models on changes (random intercepts for athlete and year), testing whether mean changes differed from zero. Standardized within-athlete effect sizes (d) were computed.
RESULTS:
BF% decreased significantly in men (−0.65 ± 1.46 %-points; −5.4%; d = −0.39; p = 0.006) but remained unchanged in women (+0.26 ± 1.67 %-points; +1.3%; p = 0.674). FFM increased modestly (women: +0.52 ± 1.02 kg; +1.1%; d = 0.47; p = 0.003; men: +0.29 ± 1.12 kg; +0.4%; d = 0.26; p = 0.008). Relative VO₂max increased significantly in both women (+1.55 ± 2.65 mL/kg/min; +2.7%; d = 0.49; p = 0.046) and men (+1.70 ± 2.15 mL/kg/min; +2.4%; d = 0.76; p = 0.002). LT₂ improved in both sexes (women: +0.08 ± 0.19 W/kg; +2.9%; d = 0.40; p = 0.005; men: +0.17 ± 0.20 W/kg; +4.7%; d = 0.74; p < 0.001). GE, relative HbM, and SJ showed small and statistically non-significant spring-to-fall changes (all p > 0.05).
CONCLUSION:
Spring-to-fall adaptations were most pronounced for aerobic performance, with typical improvements of approximately +2–3% in relative VO₂max and +3–5% in LT₂. FFM increased slightly (~0.4–1.1%), whereas BF% showed a meaningful reduction in men (~−5%) but remained stable in women. In contrast, GE, relative HbM, and SJ demonstrated limited seasonal change. These longitudinal reference values quantify the magnitude and statistical certainty of preparation-phase adaptations and provide a practical framework for interpreting routine testing results and defining realistic seasonal performance targets.
REFERENCES:
Losnegard, T., Myklebust, H., Spencer, M., & Hallen, J. (2013). Seasonal variations in VO2max, O2-cost, O2-deficit, and performance in elite cross-country skiers. J Strength Cond Res, 27(7), 1780-1790.