Do You Need a 1 % Incline on a Treadmill?

More than likely, you have heard that you need to have a 1 percent incline on a treadmill to mimic outdoor running. Some runners treat this recommendation as absolute gospel, treating a treadmill run as an inferior training session if it lacks incline. But as a result, they may miss out on optimizing treadmill runs. 

Is this recommendation accurate – or outdated? This article will examine what the research and experts say about the 1 % incline on the treadmill – and what you should be doing instead.

The Origin of the 1 % Incline Recommendation

The 1 % incline recommendation emerged from theories around the lack of wind resistance on the treadmill. 

When you run outdoors, you encounter wind resistance, even with just light breezes. The faster you run, the greater the impact of the wind resistance on the energy cost of running. A 5mph wind impacts a 5 min mile runner more than 10 min mile runner. 

The 1% incline recommendation originated in a 1996 study. This study compared 6-minute bouts of treadmill running (notably, in a temperature-controlled lab) with road running on a level surface. 

The findings of this seminal study? At paces faster than a 7:10/mile pace (4:27/km), there was a statistically significant difference between oxygen consumption (VO2) in road running conditions and a 0% grade on the treadmill. A 1% incline produced the same VO2 as road running conditions at these conditions for 5-6 min bouts.  

At some point over the years, this finding evolved from a recommendation for laboratory VO2max tests into gospel. Runners came to believe that no matter the pace or purpose of the run, they run at a 1% incline on the treadmill. 

Is a 1% Incline on A Treadmill Necessary?

1996 was more years ago than I like to admit. Since then, many studies have looked at treadmill running – 34 of which were then pooled into a 2019 systematic review and meta-analysis in Sports Medicine. 

The findings of the study gave insight into the 1% incline belief. The researchers found:

• Similar oxygen consumption at maximal intensities on the treadmill
• At faster paces, heart rate and rate of perceived exertion (RPE) were higher on the treadmill
• Heart rate was also higher at 1% on the treadmill compared to outdoors
• RPE was minorly higher with any treadmill running
•  RPE in 5K time trial with 1% incline was significantly greater than both outdoors
• Even at a 0% incline, 5K time trial performance is already worse on the treadmill
• Sprint performance was not significantly different 

The researchers’ conclusion? “As a result, it might not be possible to balance all outcomes between motorized treadmill and overground running.” At least, when considering metabolic outcomes – we’ll talk more soon about while a 1 incline on the treadmill may not be optimal from a biomechanical perspective. 

Is Running on the Treadmill Harder?

Theoretically, the higher heart rate and RPE on the treadmill could be attributed to the metabolic heat differences. As coach and exercise scientist John Davis, PhD communicates in this article, metabolic heat production also differs on the treadmill compared to outdoors. 

Without the wind resistance of outdoors, sweating becomes a less effective cooling mechanism. Running is already metabolically inefficient; only about one-quarter of the energy produced is actually used for your running. The remainder turns into heat. Your body has to work to cool down from this heat, typically via sweating. 

On the treadmill, the combination of lower air resistance and warmer ambient temperature (from the indoor locations) leads to more heat production. Most runners know this: you sweat a lot more on the treadmill than on outdoor runs, except possibly in the worst of summer. 

Additionally, the treadmill is a more constrained running environment than the outdoors. Your stride is less likely to vary as it does outdoors, despite largely comparable biomechanics. In a singular session, this monotony could feel more mentally fatiguing for some runners.

Why a 1% Incline Isn’t Biomechanically Advantageous

Over time, always running the treadmill at the exact same incline could increase your risk of overuse injury. You use your muscles in the same movements, with impact forces loading in the same manner, for thousands of steps. The risk is particularly higher for the Achilles tendon, which is loaded more on the treadmill than outdoors (according to a 2016 study.)

A simple change can reduce your risk of injury while also better mimicking the metabolic demands of outdoor runs. 

Instead of using a 1 % incline on all treadmill runs, vary your incline. Every few minutes, change the incline on your treadmill. 

Think about an outdoor run: even on flatter routes, you have slight changes. Very seldom do you run at a slight incline the whole time (as a 1% incline would biomechanically produce.) You’ll briefly run at 0.5-2% incline, some truly 0%, some slight decline. Most runners encounter even more variation in their outdoor routes. 

On the treadmill, change the incline often! You can use a preset automatic program if you have iFit or other interfaces, or you can manually change the incline. 

To mimic flatter runs or for speed workouts, vary 0-2% inclines. For a moderately hilly route, toggle between 0% and 5% inclines. If you want to mimic hills, vary between 0% and 10% on your run. 

You can be creative! Change the incline with each new song. Do ladders going up and down ever few minutes (i.e. 0%/1%/2%/3%/4%/5% every few minutes). 

In addition to better mimicking outdoor running, this variation makes a treadmill run less mentally monotonous.

Final Thoughts on 1 Percent Incline on Treadmill

It’s important not to become too granular. Don’t worry about whether or not your 6.0 mph on the treadmill is actually equivalent to a 9:50 or 10:10/mile outdoors. More than likely, the treadmill isn’t perfectly calibrated anyway.

Instead, focus on the time and intensity of your run, and vary the incline throughout. Consistent training, with mostly easy runs and some hard workouts, drives adaptation. You don’t need to precisely hit exact paces – or exact oxygen uptakes – to make a treadmill run productive.

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