By Sam Carey, Founder of Run Love Sprint.
Anyone who has finished a hilly trail race knows the feeling of trying to walk down the stairs the next morning. Trail running is booming, with more of us swapping the pavements for the North Downs, the Chilterns or a muddy loop of Epping Forest, and with races ranging from a few kilometres to well over 100. So how much does a trail race actually take out of your legs, and how long does it take to come back? A new systematic review has pulled together the research, and the answers are worth knowing before your next big day out.
What the researchers looked at
The review, Decoding Neuromuscular Fatigue in Trail Running (opens in a new tab), was published in the International Journal of Sports Physiology and Performance in May 2026 by Violeta Muñoz de la Cruz, Fernando González-Mohíno, Felipe García-Pinillos and Diego Jaén-Carrillo. They brought together 24 studies involving 674 experienced trail runners, measured before and after races ranging from around 40km up to an extraordinary 330km. Most measured how much strength runners lost in their thighs and calves, and some also took blood samples to look for signs of muscle damage.
It's worth saying up front that these were trained runners, mostly men, and the authors rated most of the studies as having a serious risk of bias. So this is a useful map of what tends to happen rather than a precise prediction for every runner.
Your legs lose a lot of strength
The headline finding is just how much strength runners lose. Across the studies, the maximum force runners could produce with their thigh muscles typically dropped by somewhere around a quarter to more than a third straight after a race, with similar drops in the calves. In one study of runners who completed a 166km mountain race, thigh strength was still around 10% below normal two days later, and still not fully back after five.
The researchers describe two kinds of fatigue at play. One is in the muscles themselves, where the fibres are damaged and can't produce as much force. The other is in the nervous system, where your brain and spinal cord become less able to switch the muscles on fully. Which one dominates seems to depend on the distance, with the nervous system playing a bigger part in shorter races and muscle damage becoming more important the longer you go.
The damage lingers for days
Blood tests tell a similar story. Markers of muscle damage, such as creatine kinase, rose sharply after every race, typically by somewhere between three and twenty times normal levels. They usually peaked between one and three days after finishing, and in the longest races they were still raised five days later. Races over 100km generally caused more damage than shorter ones, which won't surprise anyone who has run one. One study included in the review, which followed runners after a 161km race, found that those with the highest levels of muscle damage were also the most sore and took longer to get their speed back.
Do men and women recover differently?
Women make up a growing share of trail fields, so this is an important question, though only four studies looked at it directly. The overall picture was that the differences are small. Some studies found that women's calves were slightly more resistant to fatigue, while others found women lost a little more thigh strength, and there were no consistent differences in the blood markers. The authors' conclusion is that training approaches can be broadly similar for men and women, adjusted to how each person responds.
What this means for your next race
For me, the practical message is that recovery after a trail race takes longer than it feels like it should. Your legs might feel fine to jog after a few days, but the evidence suggests your strength and muscle repair can lag behind for most of a week after a long race, and longer after an ultra. Easing back in gently, rather than jumping straight into hard sessions, makes a lot of sense.
The authors also suggest preparing differently depending on the distance. For shorter trail races, they recommend strength work that trains your nervous system to recruit muscle quickly, such as heavier lifts and explosive exercises like jumps or kettlebell swings, along with sensible pacing. For longer races, where muscle damage is the bigger problem, building strength and endurance in the legs, prioritising recovery and fuelling well become more important. And whatever the distance, spending time on hills in training is the best way to prepare your legs for the punishment of the downhills, which do much of the damage.
If you're new to trail running, none of this should put you off. It's simply a reminder to respect the terrain, build up gradually and give your body the recovery it has earned.
This article is for general information and isn't a substitute for advice from a coach, physiotherapist or healthcare professional.
