Do not compare trail running distance to road running distance; elevation gain and terrain technicality are just as decisive for actual difficulty as distance.

noli's read

This advice is perfectly aligned with the science of sports physiology. Studies, notably those published in the 'Journal of Strength and Conditioning Research', confirm that the energy cost of running increases exponentially with positive gradient (elevation gain) and terrain complexity (instability). Unlike road running where pace is relatively constant, trail running imposes varied biomechanical and muscular constraints that modify caloric expenditure and accumulated fatigue. The concept of 'equivalent distance' is a method recognized by coaches for converting elevation gain into additional kilometer effort. Scientific literature also highlights that neuromuscular fatigue is greater in trail running due to marked eccentric phases during descents. There is therefore no exaggeration here: it is a pragmatic recommendation based on the principles of training load.

the sources

No named source held this one up — that absence is part of the verdict.