The percentage of time your foot is in contact with the ground between steps.
Duty Factor is closely related to Ground Contact Time, but instead of being measured in lengths of time, it is presented as a percentage. This is done because GCT changes depending on running speed, which can make analysis difficult. Duty Factor isn't as influenced by running speed, making it potentially more useful for measuring your running economy.
Find it in SportTracks
If you track runs with a sensor that records Ground Contact Time, Duty Factor can be found on your Workout Detail pages: