Mid Sweden University

INTRODUCTION: Short periods of intensified training elicit symptoms of overreaching within only 7 days (Halson et al. 2002). Despite this, block periodization of high-intensity interval training (HIT) has led to superior aerobic responses compared with traditional endurance training among trained alpine skiers and cyclists (Breil et al. 2010; Rønnestad et al. 2012).

METHODS: 21 highly-trained junior cross-country skiers (10 males, 11 females; age 16-20 y) completed 2 x 3-week training blocks in a randomized crossover design, whereby the training sessions in each 3-week block were identical but the distribution of HIT and low-intensity training (LIT) was different. In traditional periodization (TP), 3 HIT sessions (5 x 4-min at >90% HR_max) were completed each week, with LIT sessions evenly distributed over the 3-week period. In block periodization (BP) the same 9 HIT sessions were completed in week 2 and only LIT sessions were completed in weeks 1 and 3. REST-Q data was collected after each training week while resting saliva sampling (for determination of IgA and cortisol), incremental tests and performance trials were completed pre and post each 3-week period.

RESULTS: Although the overall training load (P=0.651) and total amount of work performed during HIT sessions (P=0.224) did not differ between TP and BP, the session RPE was higher and perceived recovery was lower in connection with the HIT sessions during BP (P<0.001). In addition, sport-specific stress REST-Q scores were higher following the BP-HIT week compared with all other weeks (P<0.008), whereas the global recovery-stress state was similar between all TP and BP weeks (P>0.05). Pre to post changes in salivary IgA and cortisol were also similar for TP and BP (P>0.05), although there was a tendency for IgA and cortisol to increase after TP (ES: 0.75 and 0.37) and decrease after BP (ES: 0.23 and 0.12, respectively). The change in VO₂max was greater following TP versus BP (2±4% vs -1±3%; P=0.043), whereas the changes in economy (i.e., sub-maximal VO₂) and 600-m time-trial performance did not differ between TP and BP (P>0.05).

DISCUSSION: The current study shows that highly-trained junior cross-country skiers are able to complete 9 HIT sessions at >90% HR_max within a week, with no difference in work done during the HIT sessions compared to a more traditional format of HIT-session distribution. Moreover, the REST-Q and biochemical markers indicate that BP does not lead to greater overall stress compared with TP, despite acute increases in stress following the BP-HOT week. Unlike previous studies using alpine skiers and cyclists (Breil et al. 2010; Rønnestad et al. 2012), the current findings do not support BP as a superior method for improving aerobic characteristics or performance among highly-trained cross-country skiers.

CONCLUSION: The BP intervention introduced in the current study can be tolerated by junior cross-country skiers in a highly-trained state and may be a useful training method at different stages of the season. However, it does not appear superior to TP in inducing aerobic or performance adaptations.