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Protocol

High-Intensity Intervals

Short bursts of hard cardio, such as 30 seconds to 4 minutes at a near-maximal effort, with easy recovery between them. Also called HIIT.

Pairs well withZone 2 Cardio, Resistance Training, Sprint Intervals
High-Intensity Intervals

Evidence-backed benefits

How High-Intensity Intervals can help, goal by goal, with the studies behind each score.

Endurance (Aerobic)

80XP

Interval training raises aerobic fitness (VO₂max) by about 4.5 mL/kg/min, at least as much as steady endurance training in less time.

Studies123

Fat Loss

26XP

Interval training reduced body fat about as much as steady cardio in 13 studies, in about 40% less training time, without much change in body weight.

Studies1234

How to read XP

Each score is for this protocol and that specific goal, not a general rating.

XP combines how reliable the research is with how much difference it usually makes. Higher means stronger evidence for that protocol and that goal.

Limited<15 XPModest15–27 XPModerate28–44 XPReliable45–69 XPHigh70+ XP

How to do it

One to three sessions a week with at least a day of easy movement between them. Earlier in the day suits most people.

  1. 1

    Warm up for 5–10 minutes

    Start easy and build to a brisk pace.

  2. 2

    Choose an activity that is easy on your joints

    Cycling, rowing, a hill walk, or running if you are used to it.

  3. 3

    Go hard for 30–60 seconds

    Push until you can only say a few words. A common starting plan is 6–8 rounds.

  4. 4

    Recover for 1–2 minutes

    Move slowly until your breathing settles. This is a common starting format, not a dose the trials all used.

  5. 5

    Cool down for 5 minutes

    Finish with easy movement.

The good-enough version

Six rounds of 30 seconds hard and 90 seconds easy, once a week.

Common mistakes
  • Doing it every day
  • Skipping the warm-up
  • Going all-out on the first rounds and fading
  • Using it instead of any easy cardio or strength training

Your journey

Fitness gains show within 4–8 weeks of regular sessions. An estimate from the studies' timelines, not a promise: everyone responds differently.

Endurance (Aerobic)
Week 2 → Week 8
Fat Loss
Week 6 → Week 10

From the first noticeable effect to roughly full strength. Colour follows the XP tier of each benefit.

Make it a habit

These gains come from steady use, not a single dose. Keep High-Intensity Intervals in your routine for about week 10 before you judge it.

Safety

What to know before you try High-Intensity Intervals.

Safety rating

Use with care

Dose and timing matter.

  • Check your heart firstIf you have heart disease or risk factors, or are not used to exercise, get medical clearance before pushing hard.
  • Build up slowlyStart with fewer rounds and a low-impact activity such as cycling.

Check with a doctor first if you have heart or lung disease, high blood pressure, chest pain or dizziness on exertion, are pregnant, or have been inactive for a long time.

General information, not medical advice. If you are pregnant, take medication or have a health condition, check with a doctor or pharmacist first.

Common pairings

Supplements and habits that go well with High-Intensity Intervals.

Zone 2 Cardio

Intervals raise fitness fast; easy cardio is the sustainable base. Use them together.

Resistance Training

Keep intervals to one to three sessions a week and lift on other days.

Sprint Intervals

Sprints train all-out power; longer intervals train aerobic fitness.

Build a stack around your goals.

Choose what you want to improve and see which supplements and protocols have the strongest research behind them.

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