AUTHOR=Rønnestad Bent R. , Bjerkrheim Kjetil Andre , Hansen Joar , Mølmen Knut Sindre 

TITLE=A 6-day high-intensity interval microcycle improves indicators of endurance performance in elite cross-country skiers

JOURNAL=Frontiers in Sports and Active Living

VOLUME=4

YEAR=2022

URL=https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2022.948127

DOI=10.3389/fspor.2022.948127

ISSN=2624-9367

ABSTRACT=<sec><title>Purpose</title><p>The aim of this study was to compare the effects of a 6-day high-intensity interval (HIT) block [BLOCK, <italic>n</italic> = 12, maximal oxygen uptake (V̇O<sub>2max</sub> = 69. 6 ± 4.3 mL·min<sup>−1</sup>·kg<sup>−1</sup>)] with a time-matched period with usual training (CON, <italic>n</italic> = 12, V̇O<sub>2max</sub> = 69.2 ± 4.2 mL·min<sup>−1</sup>·kg<sup>−1</sup>) in well-trained cross-country (XC) skiers on physiological determinants and indicators of endurance performance. Furthermore, the study aimed to investigate the acute physiological responses, including time ≥90% of V̇O<sub>2max</sub>, and its associated reliability during repeated HIT sessions in the HIT microcycle.</p></sec><sec><title>Methods</title><p>Before the 6-day HIT block and following 5 days of recovery after the HIT block, both groups were tested on indicators of endurance performance. To quantify time ≥90% of V̇O<sub>2max</sub> during interval sessions in the HIT block, V̇O<sub>2</sub> measurements were performed on the 1st, 2nd, and last HIT session in BLOCK.</p></sec><sec><title>Results</title><p>BLOCK had a larger improvement than CON in maximal 1-min velocity achieved during the V̇O<sub>2max</sub> test (3.1 ± 3.1% vs. 1.2 ± 1.6%, respectively; <italic>p</italic> = 0.010) and velocity corresponding to 4 mmol·L<sup>−1</sup> blood lactate (3.2 ± 2.9% vs. 0.6 ± 2.1%, respectively; <italic>p</italic> = 0.024). During submaximal exercise, BLOCK displayed a larger reduction in respiratory exchange ratio, blood lactate concentration, heart rate, and rate of perceived exertion (<italic>p</italic> &lt; 0.05) and a tendency towards less energy expenditure compared to CON (<italic>p</italic> = 0.073). The ICC of time ≥90% V̇O<sub>2max</sub> in the present study was 0.57, which indicates moderate reliability.</p></sec><sec><title>Conclusions</title><p>In well-trained XC skiers, BLOCK induced superior changes in indicators of endurance performance compared with CON, while time ≥90% of V̇O<sub>2max</sub> during the HIT sessions in the 6-day block had a moderate reliability.</p></sec>