The Science of Running

By Alex Hutchinson Ultra-trail Physiology; Trail Physiology; Fighting the Interference Effect

Ultra-trail Physiology

It’s “the world’s most challenging mountain ultramarathon,” according to the scientists who study it. And with 24,000 metres of elevation and descent spread over 330 kilometres in the Italian Alps, there’s a reason the Tor des Géants strikes fear in the hearts of runners and curiosity in the minds of researchers. What does it take to make it to the finish line of a race whose course record is just under 68 hours and whose cut-off time is a mind-numbing 150 hours?

Researchers in Italy and Switzerland convinced a 50-year-old trail veteran (and three-time Tor des Géants finisher) to serve as a guinea pig during the race. In addition to extensive physiological testing before and after, he agreed to wear a portable oxygen-analysis mask during six of the race’s gruelling ascents, along with a gps sensor and a finger-mounted oximeter to measure oxygen levels in his blood. The results, which were published in the journal Frontiers in Physiology, offer a unique glimpse of the metabolic demands of multi-day races – and some surprising twists.

The researchers expected to see a progressive decrease in the runner’s “metabolic efficiency” as he fatigued over the six days he was out there (his finishing time was 125 hours and 19 seconds), meaning that it would require more energy to cover the same distance or ascend to the same elevation. In fact, his best efficiency values were recorded on the fifth and sixth days of the race, when his fatigue was highest. The reason, the scientists suspect, is that his stride got progressively more efficient as he eliminated needless up-and-down motion and settled into a smooth (and likely dead-legged) running style.

It’s always a little risky to generalize too much based on the results of a single case report, but this new data agrees with previous findings about how efficiency changes over the course of long races. In particular, studies suggest that it’s your uphill running form that undergoes the most changes. This is, after all, the part of the race that eats up the most metabolic energy and takes the most time – in the Tor des Géants study, the participant spent a staggering 75 hours going uphill. The takeaway, the researchers argue, is that “incorporating long-lasting locomotion training… is mandatory in the training programs of mountain ultramarathon athletes.” Run hills, the longer the better, and lots of ’em.

Trail Physiology (The Short Version)

What’s true for epically long trail races like Tor des Géants doesn’t necessarily apply to briefer challenges. A recent paper in Medicine & Science in Sports & Exercise, from researchers in France, aimed to disentangle the physiological demands of “short” trail races, which they defined as anything less than the standard marathon distance of 42.2k. They put nine experienced trail runners through a comprehensive battery of tests before running a challenging 27k trail race, then assessed which test results best predicted the race times.

In standard road marathons, which take a similar amount of time to complete, performance can be predicted pretty accurately with three parameters: maximal oxygen consumption (VO2max), lactate threshold and running economy (a measure of efficiency). But these three parameters, which collectively make up the “classic endurance running model,” could explain less than half of the variation in finishing times in the trail runners. The specific challenges of trail running – terrain, footing, hills, mud – mean that successful runners need other characteristics.

Two additional parameters allowed the researchers to make better performance predictions about the trail runners. One was their running economy measured on a 10 per cent uphill slope rather than on level ground. Being an efficient runner on the f lats doesn’t necessarily mean you’re efficient on hills, and the best trail runners have apparently learned to minimize wasted motion while climbing.

The second new parameter was “local muscle endurance,” which was tested with a series of 40 all-out leg extensions. Runners whose strength declined the least from start to finish of this test performed better in the trail run – a sign, the researchers suspect, that strong legs are particularly important for propelling runners up and down hilly terrain. The takeaway, in the end, is much like the Tor des Géants study: runs hills – and lots of ’em.

Fighting the Interference Effect

Putting on muscle isn’t particularly easy for most people, but runners have long harboured the suspicion that it’s especially hard if you’re doing a lot of endurance training. Studies have mostly backed this idea up, and there’s even evidence that the cellular signals that trigger endurance gains interfere with the signals that trigger muscle growth. In people doing identical strength training programs, in other words, those who run more will gain less muscle.

As researchers learn more about molecular signalling, they’re starting to come up with ideas on how to combat this interference effect. A series of studies by Keith Baar, a Canadian-born researcher at the University of California Davis, suggests that one of the key issues is caloric deficit, which triggers a signalling cascade that hinders the formation of new muscle protein. Even if you’re getting enough calories overall, combining both strength and endurance training means there will be times during the day when you’re short on calories and getting less post-training adaption.

Baar’s practical tips include making sure you fully refuel after a run before starting strength training, and aiming to spread your protein intake throughout the day to ensure you’re never short of amino acids. He also suggests lifting relatively heavy weights that push you to failure within less than a dozen reps, which maximizes the signals for muscle growth while minimizing calories burned and metabolic stress. These factors probably only matter if you’re training at least four times a week and pushing hard in some workouts – but if you’re struggling to maintain your muscle mass, they’re worth considering. Alex Hutchinson is one of the most respected sports science writers in the world. His latest book, Endure, is available now.