What is duty factor in running?
The share of each stride a foot spends on the ground: contact time divided by stride time. Distance runners sit around 0.27–0.40; walking is above 0.5.
Duty factor expresses ground contact as a fraction of the whole gait cycle rather than in milliseconds. It is contact time divided by stride time, where a stride is two steps — left and right. Walking always has a duty factor above 0.5, because one foot lands before the other leaves the ground; running is below 0.5, because there is a flight phase when neither foot is down.
The point of the ratio is that it removes cadence from contact time. A 250 ms contact means something different at 160 steps per minute than at 190, and duty factor puts the two on the same scale. For distance running it typically falls between about 0.27 and 0.40, dropping as speed rises because contact time shortens faster than the stride does.
Researchers use it to place runners on a continuum from "aerial" (low duty factor: short contact, long flight, more bounce) to "terrestrial" (high duty factor: longer contact, shorter flight, flatter running). The useful finding is that neither end is more economical: runners at both ends of that spectrum reach similar oxygen costs at the same speed, by different mechanical routes.
That makes duty factor a description rather than a target. Trying to shorten contact deliberately tends to raise effort without improving economy, the same trap as chasing ground contact time directly. Where it earns its keep is in tracking change over time at a fixed pace — fatigue late in a long run usually pushes duty factor up as contact lengthens — and in recognising that a different running style from the textbook is not automatically a worse one.
Key numbers
| Formula | contact ÷ stride time | stride = two steps |
|---|---|---|
| Distance running | ~0.27–0.40 | falls as speed rises |
| Walking | >0.5 | no flight phase |
Duty factor from contact time and cadence
| Contact time | Cadence | Duty factor |
|---|---|---|
| 300 ms | 160 spm | 0.40 |
| 270 ms | 165 spm | 0.37 |
| 250 ms | 170 spm | 0.35 |
| 230 ms | 175 spm | 0.34 |
| 210 ms | 180 spm | 0.32 |
| 190 ms | 185 spm | 0.29 |
| 170 ms | 190 spm | 0.27 |
Each row is a plausible pairing from slower to faster running, not a target. Some papers define duty factor per step rather than per stride, which doubles every value — check the definition before comparing numbers across sources.
Work it out for yourself
Running economy calculator — See which mechanical and physiological factors actually move your oxygen cost at a given pace.
Frequently asked questions
How do you calculate duty factor?
Divide ground contact time by stride time. Stride time is two steps, so at 180 steps per minute it is 667 ms; a 210 ms contact at that cadence gives a duty factor of about 0.32.
What is a good duty factor for running?
There is no better or worse value in isolation. Low and high duty factor runners reach similar running economy at the same speed. Compare your own number at a fixed pace over time rather than against other runners.
What is the difference between duty factor and ground contact time?
Ground contact time is an absolute duration in milliseconds. Duty factor divides it by stride time, so it accounts for cadence and lets runners with different step rates be compared on one scale.
Sources
- Lussiana, Patoz, Gindre, Mourot & Hébert-Losier (2019). The implications of time on the ground on running economy: less is not always better. Journal of Experimental Biology.
- Moore (2016). Is there an economical running technique? A review of modifiable biomechanical factors. Sports Medicine.
Related explainers
Glossary: Running Economy (RE)