Terms

Elevation gain (D+) is the total height of all climbs on a course, measured in meters, not counting descents. It is a key measure of a trail race's difficulty, alongside distance.

GAP (Grade Adjusted Pace) converts your actual pace on an uphill or downhill section into an equivalent pace on flat ground, reflecting the actual effort involved.

ITRA (International Trail Running Association) is an international trail running organization that assigns difficulty categories to races and maintains a runner rating (the "ITRA index") based on their results.

A membrane is a thin waterproof but breathable layer in jackets and footwear (the best-known brand is Gore-Tex) that keeps rain out while letting body vapor escape from inside.

Trail running is running on natural paths, mountains, and rough terrain, as opposed to road running on asphalt. It usually includes a significant amount of elevation gain.

An ultramarathon is any distance longer than a classic marathon (42.195 km). Popular formats include 50 km, 50 miles, 100 km, 100 miles, as well as timed races (6, 12, 24 hours).

UTMB Index reflects a trail runner’s results. Finishing an Index race contributes to the index but does not award Running Stones.

The Vertical Kilometer (VK) is a separate trail running discipline: gaining 1000 meters of elevation over a distance usually no longer than 5 km, following the steepest possible straight line up.