REF-1449 · Rosenblat et al., 2019 · Journal of Strength and Conditioning Research · Paper · PubMed

Does polarized beat threshold training?

This 2019 pool of 3 trials said yes for time trials (ES −0.66), in trained athletes; quality 4-5/10. A later pool, about as large on this contrast, found no detectable difference. Abstract only.

Main caveat: Abstract only; closed access. Trials, sizes and heterogeneity unknown.
moderate evidenceMeasured on trained to highly trained athletes

Rosenblat, Perrotta and Vicenzino searched three databases for randomised trials comparing a polarized (POL) with a threshold (THR) training model in endurance-trained athletes. Of 329 records, 4 studies met the criteria for the qualitative analysis and 3 for the meta-analysis. Two scored 4/10 and two scored 5/10 on PEDro.

Three studies reported a time trial, 3 VO2max or VO2peak, 2 time to exhaustion and 1 economy; only the time trial had enough data to pool. The pooled moderate effect favoured POL over THR (ES −0.66, 95% CI −1.17 to −0.15). The authors say POL "may lead to a greater improvement". Our reading: this is why "polarized beats threshold" sounds settled.

The abstract names neither the included trials nor their sizes; REF-042 (B) and REF-303 (A-) are randomised POL-vs-threshold trials published before the search date and may be among them, which the abstract cannot confirm. REF-1213 (A-), searched to October 2022 with 17 studies, found no difference detectable against threshold programmes taken alone, and REF-1229 (A-) ranked threshold training first for VO2max with all credible intervals crossing zero.

The grey-zone warning stands on a thinner footing than this number suggests, while a threshold-dominant plan in well-trained athletes still has the small trials against it.

Protocol

Eligibility: random allocation; endurance-trained athletes with more than 2 years of training and VO2max or VO2peak above 50 mL/kg/min; a POL and a THR group; an internal (for example VO2max) or external (for example time trial) measure of endurance performance.
Search: SPORTDiscus (1800-present), CINAHL Complete (1981-present), Medline with Full Text (1946-present), 6 November 2016; 329 results.
Included: 4 in the qualitative analysis, 3 in the meta-analysis.
Quality: PEDro, two studies 4/10 and two 5/10.
Not in the abstract: names and sizes of the trials, sport, duration, heterogeneity, model definitions.
Funding and interests: none stated in the PubMed or Crossref record.

Key Results

OutcomeStudies reportingPooled?Result
Time trial3yesES −0.66 (95% CI −1.17 to −0.15), favours POL
VO2max or VO2peak3nonot given in the abstract
Time to exhaustion2nonot given in the abstract
Exercise economy1nonot given in the abstract
Individual response: not addressed.

Mechanisms

Measured: a pooled time-trial advantage for POL over THR across 3 trials.
Authors' interpretation: POL may improve endurance performance more than THR.
Inference: with three trials a single study can move the pooled effect a long way; REF-1213's time-trial contrast against threshold was about the same total size (114 vs the 112 it gives for this review) and found no difference; its authors put the disparity down to the number of studies, and this abstract cannot show which trials changed.

Practical Application

Does polarized beat threshold training? This 2019 pool of 3 trials said yes for time trials (ES −0.66), in trained athletes; quality 4-5/10. A later pool, about as large on this contrast, found no detectable difference. Abstract only.
How to use it: cite it as the origin of the claim, beside REF-1213 (A-) and REF-991 (A-). Not from this paper; the base's own practice: for well-trained athletes on enough hours keep threshold work a tool rather than the diet (SYNTH-27), and for time-limited athletes decide by hours (SYNTH-26).
What it does not show: anything in recreational athletes, any effect on VO2max (not pooled), or that planned tempo in a short week costs performance. It tests no sweet-spot format.

Limitations

Abstract only; closed access. Trials, sizes and heterogeneity unknown.
Three pooled trials, PEDro 4-5/10, so risk of bias is material.
Search ended in 2016; later trials and pools are not included.
One outcome pooled; the VO2max result cited elsewhere is not pooled here.
Unstable estimate: an interval of −1.17 to −0.15 from 3 trials is unstable by construction (our reading).
Funding and interests: not stated in the record.
How this entry was checked and changed
Why this level

(from the abstract) — a registered SR/MA of RCTs that the rubric's A- line would admit as "mostly small trials", held at B+ because only 3 trials were pooled, all reviewed studies scored 4-5/10 on PEDro and the search stops in 2016; a level beside REF-1213 (A-, 14 studies pooled) would overstate it