Go into any official race hotel the morning after a trail race with steep downhills, and you will see a zombie story unfold. Half-dead runners limp down the stairs to the continental breakfast, seemingly unable to make their legs work. A few might even try to go backwards down small flights of stairs to improve their odds of making it to the waffle maker in one piece.

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The reason that many runners suffer this intense muscle dysfunction in the aftermath of a downhill-heavy run is because of something called eccentric muscle contractions. As described in a seminal 1995 article in the British Journal of Sports Medicine, eccentric muscle contractions involve “the controlled lengthening of muscle under tension.”

When running down a steep slope, your knee is likely almost straight upon landing. In that position, with your knee straight, your quad muscle is at its shortest. Then, as your leg absorbs the impact, your knee bends, lengthening the muscle.

The act of lengthening a muscle while it is contracted is an eccentric muscle contraction. And these contractions do more than cause you to get sore—they can cause near-complete muscle failure. The same physiological damage that causes extreme soreness after a long downhill run or race can cause muscles to weaken prematurely during races. Luckily, with the right training, it is avoidable. Here are the basics.

Why do eccentric muscle contractions matter?

Downhill running involves a particularly high intensity of eccentric contractions, because of the muscle tension required to move fast on steep gradients without falling. Muscles essentially act as shock-absorbing springs, going from extension to compression very rapidly. This can cause extreme skeletal muscle damage—in essence, the tension can pull muscle fibers apart, much like a very unfortunate pulled pork sandwich.

These micro-tears often cause Delayed Onset Muscle Soreness (DOMS)—the culprit for those post-race zombies struggling to get to the hotel breakfast. DOMS, and associated strength loss, usually peaks around 48 hours after the run or race, but can last for a week or more. If you’ve ever gotten a post-race blood test, the doctors may have been astounded by your Creatine Phosphokinase (CPK) readings. CPK is released when, among other things, muscles are damaged or die. CPK readings often correspond with high levels of reported DOMS.

In other words, being unprepared for eccentric muscle contractions can make for unhappy muscles, unhappy blood and an unhappy trail runner.

Is there any hope?

Just one bout of downhill running can cause adaptations that reduce DOMS and muscle damage for future bouts, even when those bouts are separated by a relatively long period of time. A few mechanisms are likely involved, primarily more efficient motor-unit recruitment (you become better at the movements required for running downhill) and connective tissue changes (you become a less tender pulled pork sandwich).

How can trail runners harness the repeated bout effect?

There is no uniform protocol for exposure to eccentric muscle contractions. But, by mixing research findings with what trail runners do in practice, we can find a starting point.

1. Once a month, provide a major downhill stimulus

You need to be careful with big downhill workouts since they involve far more impact forces than flat or uphill workouts, which increases injury risk. Plus, as mentioned before, you’ll get a bit sore, and you don’t want to derail the rest of your training. By spacing big, downhill-focused workouts about four weeks apart, you’ll get the best of both worlds—adaptation to major eccentric loading without wasting too much training time on the sidelines.

The easiest way to provide a major stimulus is a downhill interval workout. Aim to get 30 to 60 minutes of hard downhill running completed, broken up by running back up the hill (you can do it all at once if you live with some good mountains nearby). 4 x 10 minutes hard downhills with jog back recovery works swimmingly, but almost any option will do. If you live in a flat place, consider investing in a treadmill that goes downhill. Or, if you’re feeling lucky, look at Youtube tutorials that describe how to set up a normal treadmill to simulate downhills.

2. At least once a week, provide a moderate stimulus

Continued exposure maximizes the benefits of the repeated bout effect. For trail runners, the easiest way to do that is to run downhills moderately hard in the course of your normal long run each week. If you live in a place with only short hills, do hard downhill repeats on the biggest hill you can find, but fewer than in the major monthly stimulus (possibly 10 minutes instead of 30-60).

Joe Gray, reigning World Mountain Running Champion, is famous for consistently hammering some downhills in many of his runs. Be like Joe (a good general guideline). This practice will have the added benefit of improving your comfort with downhills and preparing you optimally for the specific demands of running fast downhill on race day.

3. Do some leg strength involving eccentric contractions

Eccentric muscle contractions can derail a race even for the strongest runners. Understand them, and you’ll be a better trail runner (and more mobile at the post-race breakfast).

David Roche runs for HOKA One One and NATHAN, and works with runners of all abilities through his coaching service, Some Work, All Play.