# Profiling measures of muscle strength and power throughout a 156 km ultra-trail running event

## TL;DR

This study tracks muscle strength and power changes during a long ultra-trail race to understand fatigue and inform training strategies.

## Contribution

The first continuous profiling of neuromuscular fatigue throughout an entire ultra-trail race.

## Key findings

- Knee-extensor strength decreased by ~41% during the race but partially recovered post-race.
- Baseline strength differences predicted race completion likelihood, not final race ranking.
- Fatigue was localized to lower limbs with limited systemic effects.

## Abstract

Ultra-endurance performance involves complex neuromuscular demands, yet continuous in-race assessment of strength and power development is lacking. This study examined the first-ever continuous profile of neuromuscular fatigue throughout an entire ultra-trail race to understand fatigue mechanisms and inform training and pacing strategies.

Fifty-five participants (43 men, 12 women; 45.2 ± 13.6 years) attempted six identical 26 km laps with 1,000 m elevation gain and loss per lap, 14 did not complete the course. Maximum knee-extensor and handgrip strength, peak-power output, and jump-height were measured pre-race, after each lap, and 12 h post-race using standardized protocols and linear mixed models.

Knee-extensor strength decreased by ∼41% from pre-race to finish (p < .001), with substantial recovery (Δ26%–27%) at 12 h post-race. Handgrip strength showed minimal overall decline (Δ∼2%–5%), suggesting fatigue localized to the lower limbs. Peak-power and jump-height declined gradually (Δ6%–7% from early laps; p < .001). Critically, no significant relationship existed between the magnitude of strength loss and final ranking (early and late finishers showed no differences in strength profiles). However, participants who withdrew at lap 5 displayed substantially lower baseline strength (Δ27%; p = .004) and progressive strength declines compared to finishers, suggesting baseline neuromuscular capacity may influence completion likelihood.

Continuous in-race profiling reveals that ultra-trail running induces substantial and predominantly peripheral neuromuscular fatigue in the lower limbs, with limited systemic effects. While strength loss magnitude does not predict race placement among finishers, lower baseline strength may increase non-completion risk. These findings underscore the importance of targeted strength training and metabolite-clearance strategies (e.g., glycogen replenishment, hydration, recovery) in ultra-endurance preparation.