The running battle plan
Load your route — or just type a distance, a marathon has no relief to describe. You walk away with time per section, grade-adjusted pace, the fueling plan and, if you give your vVO2max, a verdict on whether the target pace holds. The engine is the energy cost equation of Minetti et al. (2002), lab-measured from −45 to +45% gradient — the published formula behind "GAP", not a black box.
The engine and its limits
Minetti's cost
On flat ground, running costs 3.6 J per kilo per metre. At +10%, 5.97 — two thirds more. The minimum sits around −20%: below that, braking costs more than gravity gives back. Your reference pace sets a metabolic engine; the gradient decides what speed it buys.
GAP
Grade-adjusted pace is the flat equivalent of your effort: 8:00/km up a 12% ramp can be worth 5:00/km of true intensity. It is the compass that stops you burning the race in the first climb.
What the lab cannot see
Minetti was measured on a treadmill: no rocks, no pack, no sixth hour. Technicality taxes the time, fatigue drift degrades the engine — two dials owned as settings. Set them from your past runs.