A Six‐Day High‐Intensity Interval Training Microcycle Improves Selected Indicators of Endurance Performance in Well‐Trained Female Cross‐Country Skiers and Biathletes

ABSTRACT We compared the effects of a 6‐day high‐intensity interval training (HIT) microcycle followed by a 5‐day active recovery period (HIT block ) with a time‐matched period of continued regular training (REG) on endurance performance in well‐trained female cross‐country skiers and biathletes. Seventeen athletes (maximal oxygen consumption (): 55.1 (5.2) mL·min −1 kg −1 ) were assigned to either HIT block or REG. No differences in training volume or intensity were observed between the groups during the 4 weeks preceding the intervention. During the intervention, HIT block completed five HIT sessions over 6 days (6 × 5‐min work intervals; target rate of perceived exertion:17–18), with increased HIT replacing part of their habitual training and thereby reducing overall training load, whereas REG continued habitual training, including 3–4 moderate‐ or high‐intensity interval sessions. Endurance performance was assessed during roller ski skating and included 15‐min time‐trial average velocity (velocity 15‐min ), velocity at 4 mmol·L −1 blood lactate (velocity 4mmol ), and velocity during the final minute of incremental testing (). HIT block demonstrated greater improvements than REG in (3.6 (2.1)% versus 1.2 (1.6)%, p = 0.024) and velocity 4mmol (4.4 (2.9)% versus 0.0 (4.4)%, p = 0.023), whereas changes in velocity 15‐min did not differ between groups (5.4 (5.0)% versus 1.3 (3.4)%, p = 0.083). An exploratory composite performance index combining these outcomes demonstrated superior improvements in HIT block compared with REG (4.5 (2.8)% versus 0.9 (2.6)%, p = 0.017). These findings indicate that a 6‐day HIT microcycle followed by a 5‐day active recovery period is associated with greater improvements in selected endurance performance indicators compared with continued regular training in well‐trained female cross‐country skiers and biathletes.