4x4 Norwegian Intervals

Four 4-minute hard efforts at ~90-95% HRmax with 3-minute easy recoveries. A strongly evidenced VO2max stimulus. High intensity; warm up fully. Default 40 min.

How often: 1–7 sessions/week · trial frequency reported by the sources of the review summary this routine was written from (4 of 8 sources named by SR05.1 state one) · planning default: 2-3x/week · the review report’s bottom line: 3 sessions/week (most consistently)

When: any time · the sources state no time of day; the planner's slot is a default

The time slot is a planning choice: a swap can keep it.

The evidence applies to the practice, not to these particular steps — they are one way to carry it out.

1
Jog (Moderate)
10 min progressive warm-up
Finish the warm-up feeling ready to work.
Slot: pre-activity preparation
Named by a Round-2 review (by reading)App-designed prescriptionthe finding states bouts, which this step does not carry; the finding states no duration for this.
9 options for this requirement
These are the practices the completed Round-2 reviews name for pre-activity preparation. The evidence rating on this routine belongs to the practice and its dose, not to any one of these. Choosing one changes what you read on this page only — it is not saved on any session in your week, and it never changes what the routine prescribes. To keep a choice, make it on the session itself in My Week.
Ballistic stretching
Compared in the review
10 papers put it in this slot · dose unit not stated
Evidence and how-to
Dynamic stretching
Compared in the review
40 papers put it in this slot · dose in sets × time
Cannot be used here: This step's dose is measured in duration and this option's in sets × time. Converting between them is not something the research says, so the swap is refused rather than converted.
Evidence and how-to
Dynamic warm-up
Compared in the review
6 papers put it in this slot · dose in duration
Evidence and how-to
Foam rolling
Compared in the review
7 papers put it in this slot · dose in duration
Evidence and how-to
Hold-relax
Compared in the review
1 paper put it in this slot (inferred by the extraction, not stated in the paper) · dose unit not stated
Evidence and how-to
PNF stretching
Compared in the review
4 papers put it in this slot · dose in duration
Evidence and how-to
Static stretching
Compared in the review
39 papers put it in this slot · dose in duration
Evidence and how-to
Strap-assisted
Compared in the review
1 paper put it in this slot · dose unit not stated
Evidence and how-to
Vibration-assisted
Compared in the review
1 paper put it in this slot · dose unit not stated
Evidence and how-to
2
4x4 Run Block (Norwegian Intervals)
4 x 4 min hard @ RPE 8-9, 3 min easy jog between
Substitute bike, rower, or treadmill to reduce impact.
Slot: long interval
Named by a Round-2 reviewMeets the finding's dose
3 options for this requirement
These are the practices the completed Round-2 reviews name for long interval. The evidence rating on this routine belongs to the practice and its dose, not to any one of these. Choosing one changes what you read on this page only — it is not saved on any session in your week, and it never changes what the routine prescribes. To keep a choice, make it on the session itself in My Week.
4x4 Norwegian intervals
Compared in the review
1 paper put it in this slot · dose in work and recovery bouts
Evidence and how-to
Cycling
Compared in the review
1 paper put it in this slot (inferred by the extraction, not stated in the paper) · dose in duration
Cannot be used here: This step's dose is measured in work and recovery bouts and this option's in duration. Converting between them is not something the research says, so the swap is refused rather than converted.
Evidence and how-to
HIIT (generic)
Compared in the review
10 papers put it in this slot · dose in duration
Cannot be used here: This step's dose is measured in work and recovery bouts and this option's in duration. Converting between them is not something the research says, so the swap is refused rather than converted.
Evidence and how-to
3
Easy Run (Zone 2)
6 min easy cool-down
Keep moving until breathing normalizes.
Slot: post-activity
Named by a Round-2 review (by reading)App-designed prescriptionthe finding states bouts, which this step does not carry; the finding states no duration for this.
5 options for this requirement
These are the practices the completed Round-2 reviews name for post-activity. The evidence rating on this routine belongs to the practice and its dose, not to any one of these. Choosing one changes what you read on this page only — it is not saved on any session in your week, and it never changes what the routine prescribes. To keep a choice, make it on the session itself in My Week.
Ballistic stretching
Compared in the review
1 paper put it in this slot (inferred by the extraction, not stated in the paper) · dose unit not stated
Evidence and how-to
Dynamic stretching
Compared in the review
3 papers put it in this slot · dose in sets × time
Cannot be used here: This step's dose is measured in duration and this option's in sets × time. Converting between them is not something the research says, so the swap is refused rather than converted.
Evidence and how-to
Foam rolling
Compared in the review
1 paper put it in this slot · dose in duration
Evidence and how-to
PNF stretching
Compared in the review
3 papers put it in this slot · dose in duration
Evidence and how-to
Static stretching
Compared in the review
8 papers put it in this slot · dose in duration
Evidence and how-to

Safety, and where each line comes from

17 product safeguard (app-authored)6 source silent

Each line below says where it comes from. “Reported by the review’s sources” is the source’s own words about adverse events or contraindications. “Product safeguard” is written by this app, not by the research. “Source silent” means the studies behind this routine report nothing on that point, which is not the same as saying it carries no risk.

Who should modify or avoid this

Product safeguard (app-authored)High intensity; build a base and get clearance if higher-risk
From this routine’s block record, written by this app.
Product safeguard (app-authored)Adults cleared for vigorous effort; cardiac patients only with supervision
From this routine’s block record, written by this app.
Product safeguard (app-authored)Designed for generally healthy adults. A heart, lung or metabolic condition, or medication that affects heart rate, changes what is appropriate here.
Source silentThe sources behind this routine's finding report no contraindications or population restrictions.

Prerequisites

Product safeguard (app-authored)Written for advanced level. Equipment: none. Warm up before the working sets, and learn each movement at a light load or short range before adding effort.
Source silentThe sources behind this routine's finding report nothing on prerequisites or starting level.

Hazards and adverse events

Product safeguard (app-authored)Jog (Moderate): Increase distance no more than ~10% per week to avoid overuse injury.
From the exercise catalogue, written by this app.
Product safeguard (app-authored)4x4 Run Block (Norwegian Intervals): High-intensity; ensure medical clearance if at cardiovascular risk and warm up fully.
From the exercise catalogue, written by this app.
Product safeguard (app-authored)Easy Run (Zone 2): If pace forces mouth-gulping breaths, slow down; build weekly mileage gradually.
From the exercise catalogue, written by this app.
Source silentThe sources behind this routine's finding report no adverse events.

Progression and regression

Product safeguard (app-authored)Jog (Moderate): regress with Easy run; Walk-jog intervals and progress with Tempo run; Outdoor run intervals.
From the exercise catalogue, written by this app.
Product safeguard (app-authored)4x4 Run Block (Norwegian Intervals): regress with Fewer reps (2-3); Shorter 3-min work bouts on a bike or rower and progress with Add a fifth rep; Push work HR closer to 95% HRmax.
From the exercise catalogue, written by this app.
Product safeguard (app-authored)Easy Run (Zone 2): regress with Walk-jog intervals; Shorter distance and progress with Long slow distance run; Tempo run.
From the exercise catalogue, written by this app.
Source silentThe sources behind this routine's finding report nothing on how to progress or regress it.

Stop conditions

Product safeguard (app-authored)Stop if you feel chest pain or pressure, faintness, unusual breathlessness for the effort, palpitations, or pain in a joint that changes how you move.
Source silentThe sources behind this routine's finding report no stop conditions.

When to seek supervision or clearance

Product safeguard (app-authored)Chest pain, pressure, or unusual shortness of breath during exertion
From this routine’s block record, written by this app.
Product safeguard (app-authored)Fainting, dizziness, or palpitations with exercise
From this routine’s block record, written by this app.
Product safeguard (app-authored)Known or suspected cardiovascular, metabolic, or renal disease without medical clearance
From this routine’s block record, written by this app.
Product safeguard (app-authored)Known cardiac disease attempting high-intensity intervals unsupervised
From this routine’s block record, written by this app.
Product safeguard (app-authored)Get clearance from a clinician before starting if you have a heart or lung condition, uncontrolled blood pressure, diabetes on medication, or symptoms on exertion; start at a lower intensity than the routine states if you are new to exercise.
Product safeguard (app-authored)Signs of a medical emergency (chest pain or pressure, trouble breathing, fainting, sudden weakness or numbness) mean 911 or your local emergency services; thoughts of self-harm or suicide mean the 988 Suicide & Crisis Lifeline. This app does not diagnose, treat or give personalised medical advice.
Source silentThe sources behind this routine's finding report nothing on supervision or clearance.

How to do it

The four-by-four-minute structure shown here, hard efforts at about 90-95% HRmax with 3-minute easy recoveries, is one product-designed way to carry out what the review summary this routine was written from reports: that interval training improves cardiorespiratory fitness. That finding reports interval training raising VO2max by roughly 5.5 mL/kg/min against about 4.9 for endurance training in healthy adults, outperforming moderate continuous training for fitness in cardiac and clinical populations, and home-based sessions matching lab-based ones - but it does not single out the 4x4 format, so these exact parameters are a design choice built on the general result rather than a separately validated protocol.

Warm up the full 10 minutes and build it progressively; you want to finish the warm-up ready to work, not merely loosened up.
Hard means RPE 8-9, roughly 90-95% HRmax: a high effort you can hold for the whole 4 minutes, not a sprint. The last rep should feel near-maximal but completable, rather than every rep being pushed to failure.
Keep the 3 minutes between reps as easy jogging rather than a full stop, so you start each rep partly recovered.
This is high-intensity work: build an aerobic base first, and get medical clearance before starting if you are at cardiovascular risk. Stop for chest pain or pressure, unusual shortness of breath, dizziness, or palpitations.
Swap the run block for a bike, rower, or treadmill to cut impact; if you do run it, let weekly mileage climb no more than about 10% at a time.
Dropping to 2-3 reps is a reasonable way in, but a shorter version is a lighter version; benefit at a shorter dose is not established here.

4×4 min hard / 3 min easy, 2–3×/week

This routine's specific parameters are a practical implementation of the practice's general finding; the finding itself doesn't validate this exact protocol.

What the evidence says

The evidence is inherited from the practice this routine implements. Any duration is allowed; the label shows where you land against the studied dose.

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).

Key sources

PreprintThe Impact of Interval Training on Cardiorespiratory Fitness, Body Composition, Physical Fitness, and Metabolic Parameters in Older Adults: a Systematic Review and Meta-AnalysisZhi-jian Wu, Zhu-ying Wang, Hao-En Gao, Xian Zhou, F. Li (2020) · 10.21203/rs.2.23869/v1 · full text

meta-analysisHome-based high-intensity interval training improves cardiorespiratory fitness: a systematic review and meta-analysisKatsunori Tsuji, Y. Tsuchiya, Hisashi Ueda, E. Ochi (2023) · BMC Sports Science, Medicine and Rehabilitation · 10.1186/s13102-023-00777-2 · full text

meta-analysisEffectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled TrialsZ. Milanović, G. Sporiš, M. Weston (2015) · Sports Medicine · 10.1007/s40279-015-0365-0 · full text

Each source is shown by its own study design.

6 sources: 5 meta-analyses, 1 systematic review

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)

meta-analysis · 2023

Tsuji et al. (2023) — Home-based high-intensity interval training improves cardiorespiratory fitness: a systematic review and meta-analysis

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

meta-analysis · 2015

Milanović et al. (2015) — Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials

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

meta-analysis · 2023

Yang et al. (2023) — HIIT vs. MICT to Improve Cardiorespiratory Fitness and Exercise Capacity in Older Adult

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

systematic review · 2024

Poon et al. (2024) — High‐intensity interval training and cardiorespiratory fitness in adults: An umbrella review of systematic reviews and meta‐analyses

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

meta-analysis · 2021

Rugbeer et al. (2021) — Comparison of High-Intensity Training Versus Moderate-Intensity Continuous Training on Cardiorespiratory Fitness and Body Fat Percentage in Persons With Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

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

meta-analysis · 2021

Poon et al. (2021) — Interval training versus moderate-intensity continuous training for cardiorespiratory fitness improvements in middle-aged and older adults: a systematic review and meta-analysis

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

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