A new study published in the journal Sports has added detailed evidence to a question that matters to almost every trail and ultra runner: why do some athletes come through a hard descent relatively unscathed while others are left with days of soreness and weakened legs? Researchers followed 36 experienced trail runners — 25 men and 11 women, all competing in a 106km ultra-trail race — and had them complete a 5km downhill run at a 15 per cent decline while holding their first ventilatory threshold intensity, then measured what happened to their muscles afterwards.
The results were unambiguous on one point: every marker of muscle damage the researchers tracked, including creatine kinase, lactate dehydrogenase and myoglobin, rose significantly in the 30 minutes following the downhill effort. But the size of that rise varied considerably between runners, and the study's more useful finding was in explaining why. Athletes who regularly built downhill repetitions into their training showed measurably lower creatine kinase responses and retained more of their half-squat strength than those who rarely trained on descents.
Gait mechanics told a similar story. Runners who adopted what the researchers termed a more 'terrestrial' pattern on the descent — shorter steps and less vertical oscillation, essentially staying lower and more compact rather than bounding down the hill — retained significantly more strength after the effort than those with a more upright, longer-striding style. Lactate dehydrogenase levels correlated strongly with the overall scale of post-race muscle damage, suggesting it could serve as a practical marker of how hard a descent has hit an athlete's legs.
For coaches and runners, the practical message is straightforward even if the underlying physiology is complex: dedicated downhill interval sessions appear to build a genuine, measurable resilience to the muscle damage that descents cause, and consciously shortening the stride and keeping the body's vertical movement low on technical or steep downhills may protect strength better than running the terrain instinctively. Isometric strength testing, of the half-squat and ankle plantar flexion in particular, gave the clearest read on how much damage an individual runner was carrying.
The findings arrive as ultra-trail race courses, from the Alps to the increasingly descent-heavy routes used across the UTMB World Series, continue to pack in more technical, steep terrain rather than less. A training approach built around structured downhill work, rather than simply accumulating vertical gain and hoping the legs adapt, looks increasingly like the more evidence-based way to prepare — a small but meaningful adjustment for any runner building toward a race with a serious net descent.