Lactate Thresholds and Performance in Young Cross-Country Skiers Before and After the Competitive Season: Insights from Laboratory Roller-Ski Tests in Normoxic and Hypoxic Conditions

Purpose: Cross-country (XC) skiing imposes high physiological demands under hypoxic conditions at altitude. Lactate thresholds such as Onset Blood Lactate Accumulation at 4 mmol/L (OBLA4) and lactate plus 1 mmol/L above baseline (Bsln+1.0) are crucial for tracking performance. This study investigates physiological responses in junior XC skiers under normoxic and hypoxic conditions before (PreCs) and after (PosCs) the competitive season. Material and Methods: 9 national-level XC skiers performed a Graded Exercise Test (GXT) on a treadmill using roller skis in both normoxic and hypoxic conditions in PreCS and PosCS. Heart rate, slope (treadmill inclination), and lactate thresholds (Bsln+1.0 and OBLA4) were measured. Results: Significant differences were found between PreCs and PosCs in hypoxia for maximum and heart rate (p< 0.05). Estimated slopes at Bsln+1.0 and OBLA4 were lower in hypoxia compared to normoxia in PreCs (p= 0.005, d = -1.29 for Bsln+1.0 and p= 0.013, d = -1.06 for OBLA4). In PosCs, lower impairment effect of hypoxia exposure under slope at OBLA4 was found (p= 0.02, d = -0.95). Positive correlations were found between heart rate and slope for Bsln+1.0 and OBLA4 in PreCs in normoxia and hypoxia, becoming stronger at PosCs, especially under hypoxia. Delta values showed: the higher the slope at Bsln+1.0 and OBLA 4 in normoxia was, the greater the decrease between normoxia and hypoxia was. Conclusion: Physiological changes in junior XC skiers after training and competition in normoxic and hypoxic conditions highlight the importance of hypoxic environments for assessing and monitoring performance throughout the season.