You move an outdoor run to a gym treadmill, enter your usual speed and add 1% incline. The adjustment is supposed to make the indoor run match the road. It is a tidy instruction, but the study behind it tested a specific group, at specific speeds, for short bouts.
A 2026 scientific Perspective revisits that familiar setting. Its authors argue that a single incline cannot reliably account for every runner, speed and testing environment. The useful question is what you want the treadmill session to reproduce.
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What the original nine runners did
In the 1996 study by Andrew Jones and Jonathan Doust, nine trained male distance runners completed six-minute efforts at six speeds, with recovery between bouts. They ran outdoors on a nearly level promenade and indoors at treadmill grades of 0%, 1%, 2% and 3%.
The tested speeds were approximately 6.5–11.2 mph. Researchers collected expired air to measure oxygen consumption, an indicator of the energy demand of running. They were comparing short exercise conditions, rather than testing a universal setting for long runs or every gym user.
At 1%, oxygen use did not differ significantly from road running at any tested speed. But at the two slowest speeds, the flat treadmill also did not differ significantly from the road. The results were more nuanced than a single mandatory incline.
Why the setting needs context
In their 2026 Perspective, Ricardo Muller Bottura and Jared Fletcher re-examine the original findings alongside later evidence. This is an interpretation of existing research, rather than a new experiment that assigns everyone a better percentage.
They discuss treadmill familiarity, surface characteristics, belt-speed fluctuations, environmental conditions and differences between runners. Air resistance matters, but a fixed incline cannot capture all those factors. Matching one physiological measurement also does not reproduce every feature of running outside.
The authors particularly question using the correction automatically when translating laboratory results to outdoor running is not the purpose. A treadmill session can have another goal, such as maintaining a chosen effort for a set time.
Choose the session before the correction
Before borrowing the number, check the activity. Slow-and-brisk walking intervals use a different pace pattern; the 1996 test examined continuous six-minute running efforts. Its results do not assign an incline to a walking routine.
For a general effort check, the CDC describes the talk test: moderate activity allows talking but not singing, while vigorous activity leaves room for only a few words before a breath. That describes relative intensity; it cannot verify that your oxygen use matches a particular outdoor pace.
If your plan calls for a comfortable run, check whether the combined speed and incline still produce that intended effort. If the plan specifically calls for hills, the incline has a different job. Decide which session you are doing before treating 1% as a required part of it.