4x4 Norwegian Intervals
Four 4-minute hard efforts with 3-minute recoveries: an interval format, one way to carry out what the sources on interval training and cardiorespiratory fitness studied, in which the gains in VO2max were greater following HIT than endurance training in healthy adults (Milanović 2015) and home-based HIIT was effective in healthy adults and patients (Tsuji 2023).
High intensity; build a base and get clearance if higher-risk
- Chest pain, pressure, or unusual shortness of breath during exertion
- Fainting, dizziness, or palpitations with exercise
- Known or suspected cardiovascular, metabolic, or renal disease without medical clearance
- Known cardiac disease attempting high-intensity intervals unsupervised
How to do it
What the evidence says
This practice is one way to carry out what the sources on the concept entry (phys.cardio.hiit-cardiorespiratory-fitness) studied: interval training and cardiorespiratory fitness, measured as VO2max or VO2peak, compared with moderate continuous training and with non-exercise control; none of them singles out the 4x4 format. Milanović 2015 (meta-analysis, 28 studies, 723 participants) reports that endurance training and HIT both elicit large improvements in the VO2max of healthy young to middle-aged adults, with the gains greater following HIT (5.5 versus 4.9 mL/kg/min). Poon 2021 (meta-analysis, 14 studies, 429 participants) reports interval training as more effective than moderate continuous training for cardiorespiratory fitness in middle-aged and older adults, and Tsuji 2023 (meta-analysis, 15 studies, 398 participants) reports home-based HIIT as an effective intervention for cardiorespiratory fitness in healthy adults and patients, comparable to lab-based HIIT and MICT. The full account, source by source, is on the concept entry this practice links to (phys.cardio.hiit-cardiorespiratory-fitness).
- 'Intervals are only for athletes' (supervised versions help patients too)
- 'Push maximally every interval' (target the prescribed hard-but-controlled effort)
- No cure claims for any disease
- No guaranteed outcomes or fixed numeric results for any individual
- Does not replace prescribed medical treatment
- A shorter or easier version will not match the full protocol's outcomes
- Agreement
- Direction recorded for 1 of 6 sources; not yet recorded for the rest.
- The claim's outcome
- Outcome not yet recorded
- Certainty
- No source states a certainty rating.
- Authors
- Sources share authors: E. Poon (first author of 2 sources).
What each source measured and concluded (6)
- What it measured
- Cardiorespiratory fitness (VO2 peak)
- How it measured it
- Gas analysis (validated method)
- Direction it states for the claim's outcome
- Improved
- How it was read
- read in full text
- What the review says it includes
- systematic review and meta-analysis
- Studies and participants, as stated
- N = 398 participants across 15 studies
- What it measured
- Maximal oxygen uptake (VO2max)
- How it measured it
- Laboratory test (validated method)
- How it was read
- read in full text
- What the review says it includes
- meta-analysis, systematic review
- Studies and participants, as stated
- N = 723 participants across 28 studies
- What it measured
- Cardiorespiratory fitness (VO2max), maximal heart rate, ventilation maximal power output, physical performance (6MWT, METs, peak power output, time up and go test), blood pressure (SBP, DBP).
- How it measured it
- Laboratory tests for VO2max; validated methods for other outcomes.
- How it was read
- read in full text
- What the review says it includes
- meta-analysis
- Studies and participants, as stated
- N = 1973 participants across 30 studies
- What it measured
- Cardiorespiratory fitness (CRF) as indicated by VO 2 max (or VO 2 peak).
- How it measured it
- Determined using an incremental exercise test to exhaustion.
- How it was read
- read in full text
- What the review says it includes
- umbrella review (review of reviews)
- Studies and participants, as stated
- N = 12,967 participants across 24 studies
- What it measured
- Cardiorespiratory fitness (CRF) and body fat percentage.
- How it was read
- read in full text
- What the review says it includes
- meta-analysis, systematic review
- Studies and participants, as stated
- N = 784 participants across 26 studies
- What it measured
- Maximal oxygen uptake (VO2max)
- How it measured it
- Laboratory test (validated method)
- How it was read
- read in full text
- What the review says it includes
- systematic review and meta-analysis
- Studies and participants, as stated
- N = 429 participants across 14 studies
Each source below is shown with its study design and a link to the original study, or, where it is not a completed research paper, with what kind of record it is; those are not counted. This is the audit trail.
Why do some records show a record type instead of a study design?
A study design is shown for a completed, peer-reviewed paper. A registered protocol, a preprint, a conference abstract, a referee report or a book chapter has not been through peer review as a finished paper, so it is labelled for what it is, and it is counted in no source count. Where a record could not be confirmed as a completed paper at all, it says so rather than guessing. They all stay in the list, and their DOI still resolves, because the count of what was screened is part of the audit trail.
- Protocol / registration A registered plan for a review or trial, not its results.
- Preprint Posted by its authors before peer review.
- Conference abstract A conference summary rather than a peer-reviewed paper.
- Peer-review report A referee's report on a paper, not the paper itself.
- Guideline / position stand A recommendation derived from evidence, which is a step further from the data than the evidence itself.
- Book chapter A chapter in a scholarly book rather than a journal paper.
- Type not recorded Our record does not say what kind of publication this is, so it is counted in no source count. That is a gap in our data, not a judgement about the research.