REF-1214 · Rønnestad et al., 2014 · Scandinavian Journal of Medicine & Science in Sports · Paper · PubMed

Should I pack five interval sessions into one week, then do one a week?

In 19 trained cyclists it raised VO2max 4.6% in 4 weeks vs no change on two a week, same total; one small trial, one lab.

Blimited evidenceMeasured on trained to highly trained athletes

Rønnestad, Hansen and Ellefsen compared two ways of organizing the same four weeks of training in trained cyclists. The block group (BP, 10 cyclists, VO2max 62 ± 2 mL/kg/min) did five high-intensity aerobic interval sessions (HIT) in week 1, then one HIT session a week for three weeks with a focus on low-intensity training (LIT).

The traditional group (TRAD, 9 cyclists, VO2max 63 ± 2) did two HIT sessions a week for four weeks among LIT. The two groups did similar volumes of HIT and of LIT. BP increased VO2max by 4.6 ± 3.7%, peak power (Wmax) by 2.1 ± 2.8% and power at 2 mmol/L lactate by 10 ± 12% (all within-group P < 0.05); TRAD did not change.

Between groups, the abstract reports a significant difference for VO2max only (P < 0.05), with effect sizes of 1.34 (VO2max), 0.85 (Wmax) and 0.71 (2-mmol power) in favour of BP. The authors conclude that block periodization gives superior adaptations over 4 weeks despite similar volume and intensity.

Our reading: a clear VO2max signal in one small trial, from a laboratory whose block results have not been reproduced by independent groups; there is no time-trial outcome in the abstract, and the citing meta-analysis by the same group states that the 2-mmol difference between groups was not significant.

Protocol

Design: two parallel groups; how cyclists were allocated is not given in the abstract. The citing meta-analysis by the same laboratory scored both 2014 Rønnestad block trials 0 for random allocation on the PEDro scale, total 4/10 (REF-946, full text, Table 2).
Participants: 19 trained cyclists; male according to the record's MeSH terms and the citing meta-analysis's table (REF-946, full text); age and training history not given in the abstract.
BP: week 1, five HIT sessions; weeks 2-4, one HIT session a week; the rest LIT.
TRAD: two HIT sessions a week for four weeks, LIT between.
Total HIT: 8 sessions in each group (5 + 1 + 1 + 1 vs 4 × 2; our arithmetic from the abstract's description). Similar LIT volume (abstract).
Session content (from [REF-946], Mølmen 2019, full-text table; not in this abstract): HIT at 88-100% of HRmax, 30 min of HIT per session; groups matched "by total and intensity-specific training volume"; HIT replaced, not added to, the cyclists' usual hard sessions; outcomes also included cycling economy and gross efficiency.
Season (from citing full texts): pre-season (REF-946: the pooled studies "were conducted in the preseason"; REF-1216: all published block trials before it, this one included, were pre-season).
Outcomes in the abstract: VO2max, Wmax and power output at 2 mmol/L blood lactate in an incremental test. When the post-tests were done relative to the loading week, the interval format and the cyclists' weekly hours are not given in the abstract.
Funding and interests: not given in the abstract.

Key Results

Outcome (4 weeks)BP (5 HIT in week 1, then 1 a week)TRAD (2 HIT a week)Between groups
VO2max+4.6 ± 3.7% (P < 0.05)no changeP < 0.05; ES 1.34
Wmax (peak power)+2.1 ± 2.8% (P < 0.05)no changeES 0.85; significance not reported in the abstract
Power at 2 mmol/L lactate+10 ± 12% (P < 0.05)no changeES 0.71; "no statistically significant differences between the groups" (REF-946, full text)
The abstract does not give TRAD's numbers, only "no changes occurred".
Large spread: the 2-mmol gain of 10 ± 12% means some block cyclists did not improve at all at that intensity (inference from the SD).
Authors' conclusion: block periodization "provides superior adaptations" to traditional organization during a 4-week period, despite similar volume and intensity — a conclusion that rests on one significant between-group outcome plus effect sizes.

Mechanisms

Measured: none beyond the test outcomes; no muscle, blood or recovery markers are reported in the abstract.
Authors' interpretation: not given in the abstract beyond the conclusion. The block rationale in the literature is overload followed by recovery, with super-compensation in the targeted capacities (REF-1216 Introduction, citing Issurin 2010 REF-1225; the REF-1225 abstract does not state it).
Inference: in BP the last three weeks before testing each held one HIT session after a five-session week, so the post-test came after a period of relative unloading of intensity; part of the difference may be freshness at the test rather than a larger adaptation. The abstract does not say how many days separated the last hard session from testing, so this cannot be checked here.

Practical Application

Should I pack five interval sessions into one week, then do one a week? In 19 trained cyclists it raised VO2max 4.6% in 4 weeks vs no change on two a week, same total; one small trial, one lab.
What the block was: 5 HIT sessions in 7 days, then 3 weeks at 1 HIT a week, everything else easy; 8 HIT sessions in 4 weeks either way. The block redistributes the hard sessions; it does not add any (the 12-week version, three such cycles, is REF-136).
Weigh it against the nulls: load-matched 12-week block vs traditional training in 30 trained cyclists (REF-098, B+), and two independent crossover trials in junior skiers (REF-1216, B+, HIT blocked into one week; REF-1217, B+ from the abstract, easy volume blocked) found no advantage. Offer a loading week as an option a trained athlete may enjoy or need for logistics, not as a proven upgrade.
Keep the one session a week after the loading week: every positive block trial in this family kept it (this trial, REF-136, REF-1215); the one block design that dropped it before testing found no gain (REF-1216) (inference across trials, not tested head to head).
Who it fits: trained male cyclists in pre-season with an established 2-sessions-a-week routine; not tested in women, in season, or in riders who do not yet tolerate two hard sessions a week (SYNTH-42 consistency gate).

Limitations

Small: 10 vs 9; allocation method not stated in the abstract, and not credited as random by the citing meta-analysis's PEDro rating (4/10).
One laboratory: the authors also ran REF-136, REF-1215 and the meta-analysis REF-946 that pooled this trial; no independent load-matched trial of the same HIT redistribution has reproduced the advantage (REF-1216, null; REF-1217 blocked easy volume, a different question), while an independent 7-day sprint overload against normal training was positive (REF-1223; per REF-946, full text, the only study with a significant performance advantage for block).
Between-group evidence: only VO2max differed significantly between groups in the abstract; Wmax and 2-mmol power rest on within-group changes and effect sizes, and the 2-mmol difference was not significant per REF-946.
No performance test: no time trial or race outcome is reported in the abstract; Wmax is a ramp-test peak.
Short: 4 weeks; whether the advantage survives the following block, or a season, was not tested here.
Unknowns from the abstract: session format, weekly hours, test timing after the last hard session, participants' age, funding and conflicts.
Men only.
Written from the abstract and record metadata, with protocol details from two citing full texts (labelled).
How this entry was checked and changed
Why this level

parallel trial, n = 19 (10 block vs 9 traditional), below the rubric's 20 for B+; read from the abstract (closed access; no open copy via Europe PMC or OpenAlex). Protocol details below that the abstract lacks come from two citing full texts and are labelled