Does Running on a Treadmill Really Require a 1% Incline?
For years, runners have been told that setting a treadmill at a 1% incline compensates for the lack of air resistance and better simulates outdoor running. But is this rule still valid? Recent research suggests it might not be as necessary as once thought—especially for recreational runners and those running at moderate speeds.
The Origins of the 1% Incline Rule
The idea of a 1% treadmill incline comes from early research by Jones & Doust (1996), which found that running on a flat treadmill resulted in a 4% lower energy cost compared to outdoor running at the same speed. To match the physiological effort of outdoor running, the researchers suggested adding a 1% incline to counteract the absence of wind resistance.
However, more recent studies have questioned whether this adjustment is needed under all conditions.
What New Research Says
Minimal Energy Differences – Miller et al. (2019) conducted a systematic review and found that oxygen consumption was only slightly lower during treadmill running (by about 0.55 ml/kg/min) compared to outdoor running. This small difference suggests that the 1% rule may not be necessary for most runners.
Speed Matters – Van Hooren et al. (2020) reviewed the biomechanics of treadmill vs. outdoor running and noted that the 1% incline correction only becomes relevant at higher speeds—typically above 10 mph (16 km/h). For slower speeds, the energy cost difference is negligible.
Biomechanics Are Comparable – Davies (1980) found that oxygen consumption and running mechanics are largely similar between treadmill and outdoor running. While minor differences exist—such as slight changes in footstrike and vertical displacement—the overall impact on performance and energy cost is minimal.
Should You Use a 1% Incline?
Based on the research, here’s when you should and shouldn’t use a 1% incline:
✅ Use a 1% incline if:
- You are running faster than 10 mph (16 km/h)
- You are training for a race where air resistance plays a role
- You want to mimic outdoor conditions at race pace
❌ You don’t need a 1% incline if:
- You are running at speeds below 10 mph (16 km/h)
- You are focused on biomechanics rather than exact energy cost
- You prefer a lower impact workout
Key Takeaways
The 1% incline rule is based on older research but is not essential for all runners.
At speeds below 10 mph (16 km/h), the difference in energy cost is too small to matter.
Oxygen consumption on a treadmill is only slightly lower than outdoor running, meaning the energy difference is minimal.
Biomechanics are similar between treadmill and outdoor running, with only slight differences in footstrike and vertical movement.
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For most recreational runners, running on a treadmill at 0% incline is just fine—especially at moderate speeds. If you’re sprinting or preparing for a race, a slight incline can help mimic outdoor conditions, but for everyday training, the 1% rule is more myth than necessity.