Incline Calculator for Trail Runners

Minetti et al. (2002) measured the energy cost of running and walking at extreme inclines on a treadmill, using oxygen consumption as a proxy for metabolic cost. The result was a 5th-degree polynomial that maps grade to energy cost — a model that has become the standard reference for trail running science.

Why downhill isn't free: At mild descents (around −10%), energy cost drops below flat running because gravity does some of the work. But at steep descents below −20%, cost rises again. The muscles must absorb kinetic energy through eccentric contractions — the same mechanism that causes post-race quad soreness after a mountain race.

The polynomial model is non-linear for a reason: running efficiency peaks near flat, deteriorates sharply on steep uphills, and the downhill optimum is around −10% to −15%. This is why race courses are designed to include some downhill — not because descent is "free" but because a specific descent range recovers energy.

Power hiking threshold: According to Koop (2021), most runners find that above approximately 15% grade, walking (power hiking) becomes more mechanically efficient than running. The energy cost of maintaining running form at steep grades is simply too high. Elite mountain runners transition earlier; recreational runners often benefit from transitioning sooner than they instinctively do.

Minetti AE et al. (2002). Energy cost of walking and running at extreme uphill and downhill slopes. J Appl Physiol. 93(3):1039–46. Koop J. (2021). Training Essentials for Ultrarunning. VeloPress.