REF-048 · Solli et al., 2025 · European Journal of Sport Science, 2025 [CORRECTED: was erroneously "Medicine & Science in Sports & Exercise"] · Paper
A 6-Day Microcycle of Short-Interval HIT Sessions Improves Endurance Indicators vs Regular Training
Participants
n=33 well-trained cyclists analysed (full text, checked 2026-09-27: 38 volunteered, 5 withdrew after the pre-test; participants were not randomized to groups). Tested before and after a 12-day period.
Protocol
BLOCK: a 6-day HIT microcycle of five HIT sessions, each 5 × 8.75 min of 30/15-s short intervals, followed by a 6-day active recovery period with reduced training load.
REG: 12 days of the cyclists' regular training, including four HIT sessions.
Key Findings
Power output over the last minute of the VO2max test (PO_VO2max): BLOCK +3.7% vs REG +0.7% (p = 0.009, ES = 1.00) — larger in BLOCK
Mean power in the 10-s sprint: BLOCK +2.8% vs REG +1.9% in the abstract; 1.5% vs −0.6% in the Results text (Table 3: 13.64 → 13.82 vs 12.69 → 12.61 W·kg−1) (corrected 2026-10-12, full text) (p = 0.028, ES = 0.63) — larger in BLOCK
No significant group difference for VO2max, power at 4 mmol·L⁻¹ lactate, 15-min maximal mean power, or gross efficiency (p = 0.156-0.919)
Performance index (PO_VO2max + PO_4mmol + PO_15-min combined): tendency towards a larger gain in BLOCK, 2.9% vs 1.2% (p = 0.079, ES = 0.71)
Authors' conclusion: a 6-day short-interval HIT microcycle followed by 6 days of active recovery improves endurance performance indicators compared with regular training in well-trained cyclists
Practical Application
In well-trained cyclists, a 6-day block of five 30/15-s short-interval HIT sessions followed by 6 easy days raised power at VO2max by 3.7% versus 0.7% with 12 days of regular training (four HIT sessions), and 10-s sprint power by 2.8% vs 1.9% in the abstract (1.5% vs −0.6% in the Results text and Table 3) (corrected 2026-10-12, full text); VO2max, 4-mmol power and 15-min power did not differ between groups — a compressed HIT week plus a recovery week is a workable way to move VO2max-level power in a short window, not a shortcut for threshold power.
Not from this paper; the base's own practice: use such a block at most a few times a season, place the five sessions across six days with the easy week honoured in full, and keep the rest of the volume in low-intensity zones.
Inference, not tested: the gain landed on the top-end measures (PO_VO2max, sprint), so a block like this suits the VO2max phase rather than a threshold phase.
Limitations
Groups were not randomized (full text); the abstract does not report the sample size.
Two weeks in total; whether the BLOCK advantage persists beyond the recovery week was not tested.
Session format was one specific 30/15 design (5 × 8.75 min); other short-interval shapes were not compared.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: two-group trial without randomization, n=33 analysed (full text)
Content correction 2026-09-27
The whole results block was unsourced: "7-day microcycle of 3-4 HIT sessions", "VO2max +4.2%", "lactate threshold +3.8%", "minimal fatigue" -> the abstract's design is a 6-day block of FIVE 30/15 sessions plus a 6-day recovery period vs 12 days regular training, and the significant BLOCK advantages were PO_VO2max (3.7 vs 0.7%) and 10-s sprint power (2.8 vs 1.9% in the abstract; 1.5 vs −0.6% in the Results text (corrected 2026-10-12, full text)); VO2max and 4-mmol power did NOT differ between groups.
Removed the "alternate 2-3 min and 4-6 min efforts" and "~75% low-intensity" prescriptions (not from this paper); remaining advice labelled as the base's own practice.
Level A -> B (non-randomized two-group trial, n=33 from the full text); title now states the actual design.
Lines labelled "full text; not checked against the abstract" were checked against the open-access full text (PMC11680548): every number in them appears there; relabelled "full text, checked 2026-09-27".
Full text (checked 2026-10-12)
Correction: the entry gives 10-s sprint mean power as "BLOCK +2.8% vs REG +1.9%"; that is the abstract's figure, but the Results text reports "1.5% vs. −0.6%, p = 0.028, and ES = 0.63", and Table 3 shows PO10-sec 13.64 (1.36) to 13.82 (1.24) W·kg−1 in BLOCK and 12.69 (1.36) to 12.61 (1.36) W·kg−1 in REG (full text, Table 3).
Thirty-eight cyclists (34 male and 4 female) volunteered; five withdrew after the pre-test because they thought the test protocol was too hard and/or did not complete it; BLOCK had 22 cyclists (21 male and 1 female, age 20.1 (3.6) years, VO2max 71.1 (6.5)) and REG had 11 (9 male and 2 female, age 23.2 (4.9) years, VO2max 71.1 (8.3)) (full text).
The microcycle sessions were on consecutive days except for a rest day on the fourth day: five series of 8.75-min (30-s at 118% / 15-s at 60% of 40-min maximal sustainable PO), power adjusted to an RPE of 16–18, with 3 min of recovery between series (first min passive), totalling 3 h 42 min of work series (full text).
The 6-day recovery period was: day 1 complete rest; day 2 rest or 20–40 min of LIT; day 3 30–90 min of LIT; day 4 20 min of LIT, two 5-min MIT intervals, a 1-min HIT interval and 10 min of LIT; day 5 rest; day 6 the same as day 4 but with three 1-min HIT intervals (full text).
HIT sessions averaged 4.25 (0.52) W·kg−1 and 71.7 (5.7)% of POVO2max in BLOCK vs 4.34 (0.85) W·kg−1 and 71.5 (10.5)% in REG, but RPE was higher in BLOCK (17.1 (0.5) vs 16.3 (1.3), p <0.001) (full text, Table 1).
During the intervention, zone 2 volume, TRIMP 1, heavy resistance training and total training volume were higher in REG than in BLOCK (full text).
Peak isokinetic knee-extension torque at 60°·s−1 fell more in REG than BLOCK (−5.4% vs. −1.2%, p = 0.016, ES = 0.78) (full text).