How should a beginner start HIIT?

Start with one or two sessions a week of short, hard intervals followed by easy recovery, for example 30 seconds hard and 90 seconds easy, repeated 6 to 8 times on a bike or while walking uphill. Build a base of regular easy cardio first if you're new to exercise. HIIT improves fitness quickly, but for fat loss it works about the same as steady cardio.

1. Warm up. 5 to 10 minutes of easy cycling, walking or jogging.
2. Work hard. 20 to 30 seconds at a hard effort, where talking is difficult. Not an all-out sprint at first.
3. Recover. 60 to 120 seconds easy, until your breathing settles.
4. Repeat. Do 6 to 8 rounds. Add rounds or shorten the rest as you get fitter.
5. Cool down. 5 minutes easy.

What the research found

• Fitness: in a 2014 review of people with conditions like heart disease, high blood pressure and obesity, HIIT improved aerobic fitness about twice as much as steady moderate cardio.
• Fat loss: a 2017 review of 31 studies found no difference in fat loss between HIIT and steady cardio, and noted HIIT wasn’t necessarily more time-efficient once you count everything.

So HIIT is a great tool for fitness, not a shortcut for fat loss.

Low-impact ways to do it

• A stationary bike or rowing machine.
• Fast uphill walking on a treadmill or a hill.
• Swimming hard lengths with rest between.
• Bodyweight moves like step-ups at a quick pace.

Save jumping and sprinting for when you’re fitter, since they’re harder on joints.