Treadmill vs outdoor running: what the meta-analyses found for effort, speed, form and load

On a treadmill the ground moves and the air doesn't; outside, you move and push through the air. That difference is small at an easy pace and grows with speed. Researchers have compared the two in dozens of crossover studies, where the same people run both ways. This page covers what two meta-analyses of those studies found, the 1% incline rule and its limits, the load under the foot, and how to use both. The machine itself has its own page: the treadmill workout.

Treadmill vs outdoor running at a glance

Where outdoor running came out ahead

• Endurance performance. Miller 2019 pooled 34 crossover studies in healthy adults. Endurance performance was poorer on a motorized treadmill than over the ground.¹ As a practical point, if your goal is a race outside, some of your runs belong outside.
• The air adds work at speed. On a treadmill there's no air resistance, so at the same speed it costs less energy than running outside.⁵ In Jones 1996, nine trained male runners ran at six speeds from 2.92 to 5.0 m/s (about 6.5 to 11 mph) on a road and on a treadmill at several grades. A 1% grade matched the road's energy cost across that range.⁵

Where the treadmill came out ahead

• Lower lactate at the same easy pace. In Miller 2019, blood lactate was lower on a motorized treadmill at submaximal speeds, at 0% and at 1% grade, while oxygen uptake was similar.¹
• Less load under the foot. In Kaplan 2014, 75 adults without symptoms, aged 19 to 72, averaged about 175% of body weight under the foot jogging on a treadmill at 8.5 km/h and about 201% jogging over the ground.³ The abstract gives no speed for the ground jog, so the two may not have been at the same pace. It's a measured force, not a prediction about anyone's joints.
• The same energy for the same distance at a moderate pace. In Hall 2004, a run of 1,600 m at 2.82 m/s (about 6.3 mph) took 481 kJ on a treadmill and 480 kJ on a track, and the walk 340 and 334 kJ; the track figures come from a subgroup of the 24.⁴ At that pace, a treadmill mile counted about the same as a track mile, so the belt gave up nothing.

Does your running form change on a treadmill?

Mostly not. Van Hooren 2020 pooled 33 crossover studies of 494 healthy people aged 18 to 65 running on a flat motorized treadmill and over the ground. Most measures of stride, joint angles, forces and muscle activity didn't differ.² Among the differences, on the treadmill:

• The foot landed flatter, with the angle between foot and ground at footstrike about 10° smaller.²
• The body bounced less, about 1.5 cm less vertical movement.²
• The foot stayed on the ground about 5 ms longer, and the peak push-off force was slightly lower.²

The authors rated the evidence for those differences low or very low, and found conflicting results for how hard the muscles worked.²

The 1% incline rule, and its limits

Setting the belt to a 1% incline comes from Jones 1996: in those nine trained men, a 1% grade matched a level road over about 5 minutes at 2.92 to 5.0 m/s. At the two slowest speeds, 2.92 and 3.33 m/s (about 6.5 and 7.5 mph), the road didn't differ significantly from a flat belt either.⁵

A 2026 review of 30 years of studies since then argues the fixed 1% may not hold for everyone: how closely a treadmill matches outdoor running depended on speed, conditions, methods and the individual.⁶ As a practical guide, not a finding: set 1% if you run faster than about 6.5 mph and want the belt to match the road; at an easy jog, a flat belt is close.

How to use both

As a practical guide, not a finding:

• Training for a race outside: do your key runs outside, where Miller 2019 found endurance performance was better.¹
• Bad weather, dark, or tight on time: the treadmill. Set 1% at faster paces.
• Easy runs by feel: either. Go by the talk test on zone 2 cardio rather than the speed, since heart rate and effort shifted a little on the belt.
• Walking, not running: the treadmill and the track matched closely at a walk in Hall 2004, which found 340 against 334 kJ for 1,600 m.⁴ Running vs walking has the comparison.

If you have pain, an injury or a medical condition, stop and ask a doctor or a physical therapist.

Common questions

Is running on a treadmill easier?

At the same speed it costs a little less energy, because there's no air to push through.⁵ In Miller 2019, oxygen uptake at easy speeds was about the same, lactate was lower, and heart rate and effort were higher on the treadmill at the faster of those speeds and lower at the slower ones.¹

Do you burn more calories running outside?

At faster speeds, slightly: that's why Jones 1996 needed a 1% grade to match the road.⁵ At about 6.3 mph, Hall 2004 measured almost the same energy for 1,600 m on a treadmill and a track, 481 and 480 kJ (about 115 kcal each, converted).⁴

Why is my pace slower outside?

No study on this page tested that question directly. Air resistance costs energy outside.⁵ As practical reasons, not findings: on a belt the pace is set for you, and hills, turns and wind change it outside.

Is treadmill walking the same as walking outside?

Close. In Hall 2004, 1,600 m of walking at about 3.2 mph used 340 kJ on a treadmill and 334 kJ on a track.⁴ Holding the rails changes that; the treadmill workout covers why.

If you'd rather have the week planned

Where you run is a small decision next to how many runs fit beside your lifting, and on which days. Coaching is the version where your workouts are built around the days you actually have, and a weekly call looks at the week you just had and rebuilds the next one around what's coming. Coaching for a week that doesn't hold still explains how that works, and apply is the first step. Otherwise: this week, do one easy run outside and one on the belt at 1%, and compare how they felt.