Jones & Doust 1996, A 1% treadmill grade reflects outdoor running cost

Study of nine habituated trained male runners. A 1% treadmill gradient made the energy cost of treadmill running equal to outdoor level running across velocities of roughly 2.92 to 5.0 m/s (about 3:48 to 5:43 per km); at slower paces no incline was needed. The basis of the “run at 1%” convention, which is a speed-dependent correction for air resistance, not a universal rule. Strong (within its tested range).