A common question for anyone buying a treadmill is whether running or walking on one is comparable to doing so outdoors. Systematic reviews of crossover studies, where the same people do both, give a more careful answer than either “identical” or “completely different”. This article summarises three of them, on running biomechanics, running physiology and performance, and walking. All involved healthy adults, and none evaluates individual treadmill brands.
Running biomechanics
Van Hooren and colleagues (2020) pooled 33 crossover studies with 494 participants comparing lower-limb biomechanics on a motorised treadmill and overground. They included only non-inclined, non-cushioned treadmill running at quasi-constant speed. The main conclusion was that spatiotemporal, kinematic, kinetic, muscle-activity and muscle-tendon outcomes were largely comparable, and most outcomes did not differ between conditions. The differences that did appear were:
- a smaller sagittal foot-ground angle at footstrike on the treadmill (mean difference 9.8 degrees, low-certainty evidence);
- differences in knee flexion at footstrike and knee flexion range of motion during stance, both graded low certainty;
- less vertical displacement of the centre of mass or pelvis (1.5 cm, low certainty);
- a slightly longer contact time (5 ms, low certainty);
- a lower peak propulsive force (0.04 body weights, very low certainty) and a difference in ankle joint moment, each based on pooled results from only two studies.
The authors advise care when extrapolating treadmill running biomechanics to overground running, particularly at footstrike. Their limitations note that most studies compared treadmill running with a laboratory runway rather than concrete or road surfaces, so real-world differences may be larger than reported. Conflicting results were found for the amplitude of muscle activity.
Running physiology and performance
A 2019 Sports Medicine systematic review of 34 crossover studies compared physiological, perceptual and performance measures. Twelve studies set the treadmill at a 1% grade and three used steeper grades. Key findings:
- oxygen uptake at submaximal speeds was similar on the treadmill at 0% and 1% grade to overground, while blood lactate was lower on the treadmill;
- heart rate and rating of perceived exertion on the treadmill were higher at faster submaximal speeds and lower at slower submaximal speeds than overground;
- at maximal running intensity, oxygen uptake and heart rate were similar between treadmill and overground;
- endurance performance was poorer on a motorised treadmill (standardised mean difference -0.50, with a confidence range shown as 0.36), while sprint performance varied considerably and was not significantly different.
The review’s conclusion is deliberately measured: some, but not all, variables differ between treadmill and overground running, and may depend on the speed at which they are assessed. That is a finding about pace-dependence and should not be read as saying a treadmill is better or worse.
Walking
A 2023 systematic review and meta-analysis of 55 studies with 1,005 healthy participants compared walking on a motorised treadmill and overground at matched speeds. It found that relative oxygen consumption (standardised mean difference 0.38) and cadence (0.22) were higher on the treadmill, while stride length (-0.36) and step length (-0.52) were lower. It reports that most kinetic variables differed between surfaces. The authors suggest the changes may reflect an attempt to increase stability given the lack of control, discomfort and unfamiliarity on the treadmill, and that treadmill construction, including surface stiffness and motor power, needs investigation.
A separate 2022 review of 22 studies with 409 young adults reached a similar overall verdict for walking: spatiotemporal, kinematic, kinetic, electromyographic and energy consumption measures were largely comparable, with some differences in kinematic, kinetic and electromyographic parameters.
What buyers can and cannot take from this
- Largely comparable does not mean identical. Small footstrike and stride differences appear, so gradual adaptation is reasonable, but the reviews give no personalised advice.
- Treadmill specifications are barely tested. The running biomechanics review excluded cushioned and inclined conditions, and the walking review says surface stiffness and motor power need investigation. Claims that a particular deck or motor makes running more natural are therefore unsupported by these reviews.
- Effort readouts may differ. Heart rate and perceived exertion depended on speed, so numbers seen on the treadmill may not map to outdoor effort at every pace.
- Endurance performance. Times on a treadmill may not match outdoor times, according to the 2019 review.
Readers comparing machines can pair this with the guides on this site covering motor ratings, deck cushioning and incline systems, which deal with specifications rather than physiology.
Frequently asked questions
Is running on a treadmill easier than running outside?
The reviews do not say so in general. Heart rate and perceived exertion were higher at faster speeds and lower at slower speeds on the treadmill, and endurance performance was poorer.
Does a 1% incline make it equivalent?
The physiology review reports similar oxygen uptake at both 0% and 1% grade, with lower lactate on the treadmill in each case. It does not present 1% as a proven correction.
Do the findings apply to everyone?
The reviews covered healthy adults aged 18 to 65 or, for one review, 20 to 40, so no conclusions follow for other groups.
The bottom line
Systematic reviews find treadmill and overground running and walking largely comparable, with specific differences in footstrike mechanics, stride length, effort at different speeds and endurance performance. The evidence is mostly low certainty and from healthy adults, and it does not test individual treadmill designs. Buyers should treat the treadmill as a good but not identical stand-in for outdoor exercise.
Sources
- Van Hooren B et al., “Is Motorized Treadmill Running Biomechanically Comparable to Overground Running? A Systematic Review and Meta-Analysis of Cross-Over Studies”, Sports Medicine, 2020
- “A Systematic Review and Meta-Analysis of Crossover Studies Comparing Physiological, Perceptual and Performance Measures Between Treadmill and Overground Running”, Sports Medicine, 2019
- “Physiological, perceptual, and biomechanical differences between treadmill and overground walking in healthy adults: A systematic review and meta-analysis”, 2023
- “Is treadmill walking biomechanically comparable to overground walking? A systematic review”, 2022