A Six-Day High-Intensity Interval Training Microcycle Improves Selected Indicators of Endurance Performance in Well-Trained Female Cross-Country Skiers and Biathletes.
Sørensen A, Odden IU, Rustaden AM, Nygaard H, Hansen J, Sandbakk Ø et al. · European journal of sport science · 2026
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 ( V˙O2max ): 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 V˙O2max testing ( velocityV˙O2max ). HIT block demonstrated greater improvements than REG in velocityV˙O2max (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.