The short answer: for energy use, treadmill and outdoor walking come out about the same, so the choice should rest on other things. Outdoor exercise is linked with better mood and more enjoyment in short experiments, though the evidence has limits. The treadmill's real advantages are convenience and control. Several figures on the earlier page, including the calorie difference, the 1 to 2% incline rule, and the joint impact reduction, didn't hold up.
| Claim on the earlier page | What we found |
|---|---|
| Outdoor walking burns 5 to 10% more calories | A 2024 meta-analysis found energy expenditure similar on treadmill and overground |
| A 1 to 2% incline "eliminates the gap" | The 1% rule comes from running studies; no walking evidence found |
| Outdoors wins decisively on mood, with 50% greater improvement | Outdoor exercise went with better mood and enjoyment in short experiments; no 50% figure found |
| Cushioned treadmill decks cut joint impact by 15 to 40% | No source found; joint kinematics were similar in the meta-analysis |
| Phone step counts are accurate to within 5% on a treadmill | A small JAMA test found -6.7% to +6.2% for phone apps |
Calories and effort
A 2024 systematic review and meta-analysis in the Journal of Sports Sciences compared treadmill and overground walking in healthy adults. It found that oxygen use relative to body weight was higher on the treadmill (strong evidence, small effect), while absolute oxygen use (moderate evidence) and energy expenditure (strong evidence) were similar between surfaces. Stride and step length were shorter and cadence faster on the treadmill, and joint kinematics were similar. A separate 2026 study in young adults went further and found higher gross and net energy expenditure on the treadmill at every speed, though that is one study. So the earlier claim that outdoor walking burns 5 to 10% more because the belt "assists" you isn't supported, and we've removed its calorie table.
The "1 to 2% incline" advice comes from running. A 1996 study (Jones and Doust) found that a 1% grade best matched the energy cost of outdoor running, because air resistance outdoors adds to the cost; later work reports that air resistance accounts for roughly 2 to 8% of running's cost depending on speed, and that the 1% rule doesn't hold at every speed. Air resistance matters much less at walking speeds, and we found no walking study supporting a grade correction. If you want more effort, use incline deliberately: incline walking has the calorie estimates, and the "12-3-30" and "5-4-30" burn figures from the earlier page are replaced there by an equation-based table.
Mood and enjoyment
A 2011 systematic review in Environmental Science & Technology (Thompson Coon and colleagues) pooled 11 studies of 833 adults who did the same walking or running indoors and outdoors on separate occasions. Compared with indoors, outdoor exercise was associated with greater revitalisation, energy and positive engagement and lower tension, confusion, anger and depression, along with more enjoyment and a greater intention to repeat the activity. The authors noted methodological limits, mood was measured soon afterwards, and none of the studies measured physical outcomes or whether people stuck with it. A 2024 meta-analysis found that outdoor environments increased enjoyment in 10 experiments. So "outdoors is better for how you feel" is supported in the short term, but "decisively" is too strong, and we couldn't find the earlier page's "50% greater improvement" figure.
The prefrontal cortex claim comes from a 2015 experiment (Bratman and colleagues, PNAS) in which a 90-minute walk in a natural setting reduced rumination and related brain activity compared with a walk beside a busy road, in 38 healthy people. It compared nature with an urban road, not with a treadmill, so it doesn't show that treadmill walking fails to do the same. See walking and mental health. We also removed the claim that morning outdoor light "resets your circadian rhythm"; morning vs evening walks explains what the research does and doesn't show.
Joints and muscles
We couldn't find a source for the claim that treadmill decks cut joint impact by 15 to 40%, and the meta-analysis found similar joint kinematics on the two surfaces. If you have arthritis or foot pain, either option can be reasonable, and a physiotherapist can advise on surfaces and footwear; walking and knee arthritis covers what has been tested. The claims that outdoor walking "engages more muscles" and trains balance more through uneven terrain are plausible but we didn't find trials, and we've presented them as untested. The meta-analysis's finding of a shorter stride and faster cadence on a treadmill is a real difference in how people walk.
Counting steps on a treadmill
In a 2015 JAMA research letter (Case and colleagues), 14 adults walked on a treadmill at 3.0 mph for 500 and 1,500 steps, twice each, and ten apps and devices were compared with an observer's tally. Smartphone apps were within -6.7% to +6.2% of the observed count, pedometers and accelerometers within -0.3% to 1.0%, and wearable devices were off by -22.7% to -1.5%. That is a short, controlled test, so "within 5%" is a little optimistic, and over long periods, different phone apps can diverge more. A phone left on the console won't register steps because nothing is moving it, so keep it in your pocket. If you want an hourly activity chart, StepMax, our own free app, has one: Android, iPhone.
How we'd choose
This part is opinion. The treadmill removes weather, darkness and traffic from the decision, and if it is what gets you walking on bad days, that is a good reason to use it. Outdoors adds light, scenery and company, and the short-term mood evidence leans its way. Using both is reasonable, and the earlier page's weekly split is a sensible example, though it isn't a studied protocol. If you walk outdoors in bad weather instead, walking in winter and walking in the rain cover the practical side, and how to walk 10,000 steps has ways to fit the steps in.
Sources
- Physiological, perceptual, and biomechanical differences between treadmill and overground walking in healthy adults: a systematic review and meta-analysis. Journal of Sports Sciences. 2024. tandfonline.com
- Use treadmills with caution: walking energy expenditure and metabolic cost are elevated compared to overground across multiple speeds in healthy young adults. Journal of Functional Morphology and Kinesiology. 2026. doi
- Jones AM, Doust JH. A 1% treadmill grade most accurately reflects the energetic cost of outdoor running. Journal of Sports Sciences. 1996;14(4):321-327. researchgate.net
- Beyond the 1% treadmill rule: 30 years of evidence on treadmill and overground running economy. Applied Physiology, Nutrition, and Metabolism. cdnsciencepub.com
- Thompson Coon J, Boddy K, Stein K, Whear R, Barton J, Depledge MH. Does participating in physical activity in outdoor natural environments have a greater effect on physical and mental wellbeing than physical activity indoors? A systematic review. Environmental Science & Technology. 2011;45(5):1761-1772. NCBI
- Acute effects of outdoor versus indoor exercise: a systematic review and meta-analysis. 2024. tandfonline.com
- Bratman GN, Hamilton JP, Hahn KS, Daily GC, Gross JJ. Nature experience reduces rumination and subgenual prefrontal cortex activation. PNAS. 2015;112(28):8567-8572. doi
- Case MA, Burwick HA, Volpp KG, Patel MS. Accuracy of smartphone applications and wearable devices for tracking physical activity data. JAMA. 2015;313(6):625-626. jamanetwork.com
Correction note: an earlier version of this page said outdoor walking burns 5 to 10% more calories than treadmill walking and that a 1 to 2% incline eliminates the gap, gave a calorie table, said outdoors wins decisively on mood with a 50% greater improvement, said cushioned decks cut joint impact by 15 to 40%, said outdoor walking engages more muscles, said phone step counts are accurate to within 5% on a treadmill, and gave burn figures for the 12-3-30 and 5-4-30 routines. We could not support most of those, so they were removed or corrected. The 2024 meta-analysis and the Thompson Coon review are cited from abstracts and summaries, and we do not have the 2024 and 2026 papers' author lists. This article is for informational purposes and does not replace medical advice. This is general information, not medical advice.