There are a lot of things that can go wrong in an ultramarathon, from mundane blisters to—as for ultra legend Jim Walmsley at the 2016 Western States hundred-miler—getting swept downstream while trying to cross a river. But if you can dodge these sorts of logistical bullets, it’s surprisingly hard to put your finger on what ultimately limits ultra performance. For marathons and shorter races, it’s all about oxygen: the fastest finishers tend to have high VO2 max and running economy. But researchers have repeatedly found that these oxygen-related measurements are poor predictors of how you’ll fare in an ultra.
In a recent issue of the journal Sports Medicine, physiologists Nick Tiller and Guillaume Millet—both devoted ultrarunners and longtime ultra researchers—make the case that the key impediment to ultrarunning performance is muscle damage. They offer several lines of evidence for this claim, most notably that this is what ultrarunners themselves seem to think. In an online survey of 824 ultrarunners, a remarkable 66 per cent pointed the finger at muscle damage as their kryptonite, compared to just 23 per cent voting for gastrointestinal distress. Nothing else got more than seven per cent of the vote.
Physiological findings point in the same direction. For example, blood tests of an enzyme called creatine kinase offer a rough estimate of how much muscle damage you’ve sustained. Normal levels are around 100 units per litre; that can soar to 1,000 units per litre after a marathon, and more than 10,000 units per litre after an ultra—a level that, under any other circumstances, would signal some sort of catastrophe in progress. This accumulated structural damage interferes with muscle contraction, and perhaps more importantly, it can make every step excruciating. Crucially, it’s irreversible, at least temporarily. If you’re struggling with GI problems, you can slow down or try different fuelling strategies. But once your legs are shot, you’re done for the day.
Prepping for damage
Your number one job in training for an ultra, then, is to harden your leg muscles against the pounding they’re going to endure. The simplest approach, Tiller and Millet suggest, is—wait for it—to run a lot. The evidence here is more observational and anecdotal than scientific, but it’s likely that higher mileage inflicts enough damage on a regular basis that your muscles adapt to become hardier.
For a more targeted approach, you can try downhill running. The eccentric muscle contractions caused by “braking” with each step as you descend are especially likely to cause muscle damage, which in turn leads the muscles to be rebuilt with greater resistance to damage. That’s the same rationale for why Boston Marathoners are often advised to incorporate downhill training in their preparation for the race’s opening miles (which are downhill). Finding prolonged stretches of downhill can be challenging; if you’re lucky enough to have access to a treadmill with downhill grades (or are willing to risk propping up the back of your treadmill), that’s another option.
Tiller and Millet don’t mention strength training, but some physiologists think that heavy resistance exercise also offers some extra defence against muscle damage. Back in 2017, Spanish sports scientists published findings that foreshadowed Tiller and Millet’s paper: they found that muscle damage, as quantified by creatine kinase levels, was the best predictor of whether runners in the Madrid Marathon would hit the wall. Lead researcher Juan del Coso’s suggestion for warding off muscle damage was to do lower-body strength exercises, such as weighted lunges and squats.
Poles (and other solutions)
Once the race begins, the focus shifts to minimizing the damage you incur. One of the most powerful strategies is using trekking poles, which shift some of the load of each footstrike from your legs to your upper body. The popularity of poles in trail and mountain ultras is actually one of the key pieces of evidence for the claim that muscle damage is the ultrarunner’s greatest foe. Poles add weight and make runners less efficient, meaning they have to burn more energy to cover a given distance. But in exchange, they “save the legs” by reducing muscle damage—and experienced ultrarunners generally conclude that this trade-off is worthwhile.
Another evidence-backed tactic is taking shorter strides (or, equivalently, increasing your stride rate). Reducing your stride length by as little as 10 per cent seems to reduce up-and-down motion and soften the landings’ impact on your muscles. This technique is particularly effective on downhills, where the landing forces are highest and muscle damage is most severe. If there’s one mantra you take from this article, it should probably be “short strides on the descents.”
Then we get into the sketchier ideas. Tiller and Millet are open to the possibility that extra protein might be helpful for races longer than 100K. The protein provides building blocks—amino acids—for the ongoing process of muscle repair during the race. They note one study which found that successful Western States finishers averaged an intake of 0.08 grams of protein per kilogram of body weight per hour, while those who dropped out of the race averaged only 0.04 g/kg/h. On the other hand, they’re skeptical about the effectiveness of other dietary supplements, and of popular approaches such as compression socks and muscle taping.
One final note of caution: you might think the solution to the pain of muscle damage is simple: start popping nonsteroidal anti-inflammatory drugs like ibuprofen early and often. In the past, surveys have found that between 50 and 70 per cent of ultrarunners report using NSAIDs during races. But there’s growing awareness that the potential side-effects of NSAID use on your kidneys, gut and other organs might be worsened with prolonged running, so sports nutritionists strongly discourage the use of “vitamin I”—and NSAIDs are banned at many races, including UTMB. Instead, stick to the basics—big mileage, downhill training, poles, shorter strides—and with any luck, you might find that blisters and gut issues are your biggest challenges, after all.
Alex Hutchinson is a Toronto journalist specializing in the science of running and other endurance sports. His latest book is The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.
