Muscle load in trail running. A prospective n-of-1 series to separate eccentric dose from response

A field Index of eccentric dose in trail running has been proposed, built only from external variables (body and carried mass, elevation loss and gradient) and weighted by recent exposure history to model the repeated bout effect (Inzaurralde, 2026, SportRxiv preprint v0.3). This registration covers the first validation stage, a prospective n-of-1 series of about 15 weeks in which Gonzalo Inzaurralde (G.I.) is the only participant. One session per week is followed by jump and soreness measurements before the session and on the following two mornings, and a block of six prescribed descents assigns descending speed by protocol. The series is exploratory, and every hypothesis is decided in a later cohort stage, which will be preregistered separately before recruitment. The aim of this registration is to fix in advance the outcomes, models, estimation order and decision rules of the series.