HIIT vs LISS: which cardio is better for fat loss?

The two types, defined

HIIT (high-intensity interval training) alternates short, hard efforts with recovery. A typical session is 6 to 10 rounds of 20 to 60 seconds hard, with equal or longer easy periods, totalling 15 to 25 minutes including warm-up.

LISS (low-intensity steady state) is continuous work at an easy to moderate pace: brisk walking, easy cycling, rowing or swimming for 30 to 60 minutes. You can hold a conversation throughout.

Between them sits moderate-intensity continuous training, such as a steady 30-minute jog, which many studies use as the comparison.

Use the heart rate zone calculator to find your own numbers.

What the research says about fat loss

Head-to-head studies show that both approaches reduce body fat, and the difference between them is small. A meta-analysis by Wewege et al. (Obesity Reviews, 2017) found that interval training and moderate continuous training produced similar reductions in body fat, with intervals taking roughly 40 percent less time.

Some later analyses, such as Viana et al. (British Journal of Sports Medicine, 2019), reported a modestly greater fat loss with interval training, particularly sprint intervals. Even there, the absolute differences were small compared with the effect of diet.

The so-called afterburn (excess post-exercise oxygen consumption) is real but modest, usually adding only a few dozen extra calories, not the hundreds often claimed.

Fat loss is also not the only reason to do cardio. The World Health Organization recommends adults get 150 to 300 minutes of moderate activity, or 75 to 150 minutes of vigorous activity, each week, alongside muscle strengthening on two or more days. Both HIIT and LISS count towards that, and both improve heart health, blood pressure and blood sugar control.

Calories burned: a realistic comparison

Per minute, HIIT burns more. Per session, longer steady cardio often matches or beats it, because you can do much more of it. Rough figures for a 75 kg (165 lb) person:

Estimates vary with fitness and body size. Get a figure for your own weight with the calories burned calculator.

How each affects your lifting

Cardio and strength training compete for recovery. This is called the interference effect, and it is strongest when cardio is high-impact, high-volume, and done close to leg training.

• HIIT is demanding on the legs and nervous system. Two or three sessions a week can eat into squat and deadlift performance if placed badly.
• LISS, especially walking or cycling, has little effect on lifting and may help recovery.
• Running has more impact than cycling or rowing, so it interferes more with leg training.

If muscle and strength are your priority, lean towards LISS and keep HIIT to one or two short sessions. Separate hard cardio from leg days by at least 24 hours, or do it after lifting rather than before.

Don't overlook steps

Non-exercise activity, such as walking around, taking stairs and standing, often burns more calories across a week than formal cardio. It also tends to drop without you noticing when you diet, which is one reason fat loss slows.

A daily step target is the simplest form of LISS. Moving from 4,000 to 9,000 steps a day can add roughly 200 to 300 calories of daily burn for many people, with almost no recovery cost.

Who should choose which

Ask your doctor before starting HIIT if you have heart disease, high blood pressure, or have been inactive for a long time.

Most people end up doing best with a mix: plenty of easy movement as the base, plus a small dose of hard intervals once fitness allows. The easy work burns calories and aids recovery; the intervals build fitness quickly and keep sessions short.

Whatever you choose, judge it after six to eight weeks by your weekly average weight, waist measurement and how your lifting is going, not by how exhausted a single session leaves you.

A weekly plan that combines both

This template works alongside three or four lifting sessions, for example the fat loss workout plan or an upper lower split:

Plus a daily step target of 7,000 to 10,000. Start with less if you are new and add one session every week or two.

Choosing the best LISS for you

The best steady cardio is the one you will do three to five times a week without dreading it or getting hurt. Each option has a different trade-off:

Incline treadmill walking deserves a mention: at a 10 to 12 percent incline and a moderate pace, it pushes your heart rate up without the impact of running, and it barely touches your lifting recovery.

Common cardio mistakes

• Eating it back: fitness trackers often overestimate calories burned, and many people eat more after cardio. Do not add cardio calories back to your diet unless you are losing weight faster than planned.
• Doing HIIT too often: intervals done four or five times a week stop being high intensity. Quality drops and fatigue builds.
• All grey-zone effort: many people do every session at a medium-hard pace that is neither easy enough to recover from nor hard enough to count as intervals. Make easy days easy and hard days hard.
• Starting too big: going from zero to an hour a day leads to sore joints and quitting. Add 10 to 15 minutes per week.
• Replacing lifting with cardio: while dieting, lifting is what tells your body to keep muscle. Keep it in.

A simple HIIT session to start with

1. Warm up for 5 minutes at an easy pace on a bike or rower.
2. Go hard for 30 seconds, at roughly 8 out of 10 effort.
3. Recover for 90 seconds at an easy pace.
4. Repeat 6 times. Add a round every week up to 10.
5. Cool down for 5 minutes.

Bikes and rowers are safer for intervals than sprinting, which has a higher injury risk if you have not sprinted in years. As fitness improves, shorten recovery to 60 seconds before adding rounds.