Treadmill vs Outdoor Walking: a PT Reveals Which Is Better for Fat loss, Strength and Fitness

Some people have very strong feelings about how they get their daily steps in. There are the early risers who can't sit down at their desks until their feet have made contact with the earth, while others swear by a quick lunchtime treadmill sesh.

But when it comes to the health and fitness benefits, is one actually better than the other?

Truth is, there isn’t really a ‘best’ option, says personal trainer Kate Rowe-Ham. Both treadmill and outdoor walking have benefits, and the right choice depends largely on your goals, circumstances and which one you'll actually do consistently.

Below, we break down how treadmill and outdoor walking compare for fat loss, strength and cardiovascular fitness – plus when you might want to choose one over the other.

‘The treadmill is a consistency tool: weather-proof, kind to joints and you can dial in the exact incline you want,’ notes Rowe-Ham.

That ability to control the incline can make it particularly useful when you want to increase the intensity of your walk. A small study published in the International Journal of Exercise Science last year compared the viral 12-3-30 walking workout with self-paced running.

While overall calorie expenditure was similar, a greater proportion of energy came from fat during incline walking: around 40%, compared with 33% during running.

Of course, incline walking isn’t limited to treadmills. A treadmill simply removes some of the logistical barriers – namely finding a suitable hill – while allowing you to control the gradient precisely.

Walking outdoors, meanwhile, comes with its own advantages. If safe and suitable, it can offer additional mental health and wellbeing benefits, says Rowe-Ham, including ‘better sleep, better mood and [more] vitamin D’, while varied terrain can also challenge your balance.

‘Walking in green space literally calms the brain’s stress centre,’ she adds.

One study comparing walking in an outdoor natural environment with walking in an indoor simulated natural environment found that participants' heart rates were higher outdoors without a corresponding increase in perceived exertion. In other words, they appeared to work harder without feeling as though they were.

Both environments were associated with mood benefits, however. The outdoor group reported feeling more energised afterwards, while the indoor group experienced a reduction in tension.

If your goal is sustainable fat loss, says Rowe-Ham, treadmill and outdoor walking are fairly evenly matched.

‘A step is a step; what matters is how much and how often you walk, so whichever gets you moving more wins,’ she notes.

What if building strength is the aim? While ‘neither builds real muscle on its own’ – you'll need resistance training for that – Rowe-Ham says ‘incline treadmill walking at 10-15% is the better glute and leg workout’.

For general cardiovascular fitness, both are useful. ‘Treadmill edges it for structured intervals; outdoors edges it for those long, easy walks that build your aerobic base,’ says Rowe-Ham.

So rather than picking a winner, incorporating both could give you the best of each: the treadmill for controlled, structured sessions and outdoor walking for longer, lower-intensity movement.

There are also a few persistent myths about how treadmill and outdoor walking compare.

1. You Need a 1% Treadmill Incline to Mimic Walking Outdoors

You may have heard that setting a treadmill to a 1% incline replicates the energy demands of moving outside. But that rule originates from running research, notes Rowe-Ham.

‘At walking speeds, the calorie difference is tiny.’

The bigger difference may be in how you move.

‘On a treadmill, we all walk a bit more cautiously, with shorter strides and quicker steps. Outdoors, you’re dealing with different elements: kerbs, cambers, slopes and turns, which wake up all the little stabilising muscles around your ankles and hips.’

Rowe-Ham herself used to favour the treadmill before becoming a convert to outdoor exercise.

‘I used to be a total treadmill runner: controlled, predictable, job done, but once I learned about the outdoor benefits and what that uneven ground was doing for my balance and bones, it won me over.’

2. The Treadmill Belt Does Some of the Work for You

Not at typical walking speeds, says Rowe-Ham.

‘The belt doesn’t do the work for you at walking speeds; that’s a myth nicked from running research.’

And don't put too much faith in the calorie figure flashing up on the screen, either.

‘The treadmill calorie readout is often 20% off either way – that’s the machine, not you.’

3. Outdoor Steps Automatically Count for More

‘10,000 steps outdoors doesn’t magically beat 10,000 indoors, step for step,’ says Rowe-Ham. ‘The extra value outside comes from light, nature and terrain.’

In other words, the steps themselves aren't inherently more valuable simply because you accumulated them outside. It's the additional environmental factors that may provide benefits.

Ultimately, the best option is the one you'll do consistently.

Rowe-Ham now opts for outdoor walking whenever possible – not least because she doesn’t have a treadmill at home.

‘I spent years loyal to the machine, and it served me well, but the day I took my walks outside properly, something shifted,’ she says. ‘My head felt clearer, the walks felt shorter and I actually looked forward to them.’

Her advice? Use both according to what you need that day.

‘Treadmill when the weather’s grim, it’s dark or steps need to happen while you’re on calls. Outdoors when you need the head-clearing as much as the steps, and when balance and bone-loading matter, which, for women in midlife, is most of the time.’

And given that the average person in the UK reportedly spends just 7% of their working week – around 86 minutes a day – outdoors, according to Loughborough University, a walk can also be an easy way to get a little more fresh air into your day.

The bottom line? There's no need to pick a team. The treadmill offers convenience, consistency and precise control over your workout; walking outdoors adds variable terrain, daylight and time in nature. Whichever gets you walking more is likely to be the better choice for you.

If there’s one thing Kori Sampson knows, it’s how to optimise your body composition for performance. To tap into his knowledge as an elite athlete and coach, we asked him to create a 4-week plan to help you move faster, recover quicker and keep pushing when the fatigue sets in – all while improving your muscle-to-fat ratio.

Ready to build muscle, burn fat and come out the other side looking, feeling and performing better? Click here to get 14 days of free access to the plan via the Men’s Health app.

Hannah Bradfield

Senior Health and Fitness Writer

Hannah Bradfield is a Senior Health and Fitness Writer for Women’s Health UK. An NCTJ-accredited journalist, Hannah graduated from Loughborough University with a BA in English and Sport Science and an MA in Media and Cultural Analysis.  She has been covering sports, health and fitness for the last five years and has created content for outlets including BBC Sport, BBC Sounds, Runner’s World and Stylist. She especially enjoys interviewing those working within the community to improve access to sport, exercise and wellness. Hannah is a 2024 John Schofield Trust Fellow and was also named a 2022 Rising Star in Journalism by The Printing Charity.  A keen runner, Hannah was firmly a sprinter growing up (also dabbling in long jump) but has since transitioned to longer-distance running. While 10K is her favoured race distance, she loves running or volunteering at parkrun every Saturday, followed, of course, by pastries. She’s always looking for fun new runs and races to do and brunch spots to try.