More than likely, you have heard that you need to have a 1% incline on a treadmill to mimic outdoor running. Some runners treat this recommendation as absolute gospel, considering a treadmill run inferior if it lacks an incline.
However, this belief may actually prevent runners from optimizing their treadmill workouts.
Is this recommendation accurate or outdated?
This article examines the research and expert insights regarding the 1% incline rule and explores what you should be doing instead.
The 1% incline recommendation stems from theories about the lack of wind resistance on a treadmill. When you run outdoors, even light breezes create wind resistance, with faster speeds amplifying its effect.
A 1996 study compared 6-minute bouts of treadmill running (in a temperature-controlled lab) with road running on a level surface.
The study found that at speeds faster than 7:10/mile pace (4:27/km), there was a significant difference in oxygen consumption (VO2) between road running and treadmill running at a 0% incline. A 1% incline produced the same VO2 as road running in these conditions.
Over the years, this evolved from a recommendation for laboratory VO2 max tests into a general assumption that every treadmill run should have a 1% incline.
Since 1996, numerous studies have examined treadmill running. A 2019 systematic review in Sports Medicine analyzed 34 studies on the topic. The findings provided deeper insight into the 1% incline belief:
The study concluded: "It might not be possible to balance all outcomes between treadmill and outdoor running." This suggests that treadmill running differs from outdoor running in ways that a simple 1% incline cannot fully replicate.
Higher heart rate and RPE on the treadmill could be due to metabolic heat production differences. According to exercise scientist John Davis, PhD, metabolic heat builds up more on a treadmill due to reduced air resistance and warmer indoor environments.
Since running is metabolically inefficient only about 25% of energy goes toward movement, while the rest converts to heat—your body has to work harder to cool down indoors, often leading to excessive sweating.
Additionally, treadmill running restricts natural variations in stride, making it feel mentally and physically more monotonous than outdoor running.
Constantly using a 1% incline on the treadmill could increase your risk of overuse injury. Repetitive motion without variation loads muscles, tendons, and joints the same way for thousands of steps. A 2016 study found that the Achilles tendon experiences greater strain on the treadmill than on outdoor surfaces.
A simple fix? Vary your incline instead of keeping it at 1% throughout the run.Think about an outdoor run—even on flat routes, you encounter slight natural variations.
Instead of a steady 1% incline, incorporate changes to better mimic real-world running conditions and reduce injury risk.
How to Adjust Incline for More Effective Treadmill Runs
Using a preset automatic program or manually adjusting incline makes treadmill running more engaging and biomechanically beneficial.
Avoid getting too granular about whether 6.0 mph on the treadmill equates to a 9:50 or 10:10/mile pace outdoors. Most treadmills aren’t perfectly calibrated anyway.
Instead, focus on time, effort, and variation in your workouts.
Regular training balancing easy runs and strategic workouts, drives performance improvements more than fixating on incline percentages.
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