There’s a lot to be said for getting off the asphalt and onto the trails, whether it’s on two wheels or two legs. Apart from the peace of being away from traffic and the joy of splashing through the occasional mud puddle, there’s less exposure to vehicle-based pollutants like particulate matter and nitrogen oxides. Studies also demonstrate the physical benefits of “nature bathing”—being exposed to nature and green spaces—as markers of cardiovascular health.
Much like gravel and bikepacking races have taken cyclists off the road and extended their concept of endurance, the emerging popularity of trail running has taken many runners off road and for longer durations than the typical half or full marathon.
Studying Ultra Running
The idea of studying what physiological measures predict trail-running success is not new. However, a common limitation to most previous studies is that they have taken an epidemiological approach of comparing results from many different events. Because each trail-running event can be so unique, it becomes difficult to compare across them. Several studies examine one event in a single duration, such that we can’t compare across events of different durations.
Recently, separate studies from Canada and France have taken a different approach. They examined a single ultra-trail event, testing male and female runners who completed different distances ranging from shorter to longer. Better yet, they performed specific anthropometric and physiological testing in the lab on these runners before and/or after the event.
The Canadian study tested runners competing at 50km (31mi), 80km (49.7mi), or 160km (99.4mi), on a 20-kilometer (12.4mi) course with about 620m of elevation gain per lap. Conducting the race on a loop over the course of one day meant that race and weather conditions affected all runners equally. They did lab tests on the runners in the prior month that included training history, anthropometrics, cardiovascular measures (i.e., blood pressure, heart rate, heart rate variability, and hematocrit), and a treadmill VO2max test to exhaustion.
The French study tested runners completing the Ultra-Trail du Mont-Blanc, with distances ranging from 40km (24.8mi) to 171km (106mi, with 10,000m of climbing!). Along with fitness testing, runners were also tested for lower-body strength 24-48 hours before their race and immediately afterwards. Unlike the Canadian study, the races were held on different courses over the span of one week, with temperatures ranging from 11°C to 31°C (50°F to 88°F).
Predictors of Performance in Ultra Runners
Let’s get to the biggest findings from the studies, which were overall consistent in their outcomes.
- VO2max and running speed at VO2max were strong predictors of performance for the short races in both studies. The authors concluded that the predictors for performance with shorter trail races were roughly analogous to those of the marathon. This was interesting because, while the trail racing distances were similar, the amount of elevation gain and loss were exponentially greater, resulting in more variability in speed than steady effort on the road.
- The French study found that the rate of lipid oxidation was related to performance in the short distances. This is somewhat counterintuitive, as we typically consider lipid oxidation more dominant with longer efforts. The authors posed one theory that lower intensities and slower speeds with longer distances permit a greater rate of eating—especially carbohydrate ingestion—making the rate of fat oxidation less critical for performance.
- At medium distances, pure aerobic capacity became less important, with running speed at VO2max the primary variable related to performance.
- Surprisingly, running economy was not correlated with performance at any distance. But remember that running economy was tested on a treadmill and not outdoors. Trail running may favor low running economy to deal with the uneven surfaces and elevation gains.
- The Canadian study included an analysis of whether anything was a good predictor for not finishing the trail races. The dominant difference in non-finishers appeared to be lower training volume. This suggests that it really isn’t possible to fake an ultra run if you don’t put in the appropriate volume.
- At the same time, the Canadian study also found that training volume over the past month and year were only predictive of performance up to 50km (31mi)—not of the longer distances. One possible extrapolation from this is that there is a minimum threshold of volume required to prepare for ultra running, and after this threshold more is not necessarily better.
- No relationships were found for any measures with performance at the long distances. This highlights that race management may be more important than any physical measure. Some examples of race management include proper pacing, injury avoidance (e.g., navigating technical sections slower but safer), nutrition and fluid management, and mental toughness.
The main takeaway from these two studies is that shorter ultra races focus on aerobic fitness. So if you’re coming from a half- or full-marathon background, these shorter ultra races may be a better transition for you than trying to tackle the longest races right away.
If you want to get into longer ultra races, you need a minimum training volume to enable your body to handle the extra pounding from longer distances. However, too much volume can lead to greater injury risk. With no clear predictors of performance, longer-distance ultra runners should emphasize the intangibles of race management to last the whole way.
These studies show that practice and experience are critical to success in ultra running. No matter if you choose to tackle shorter or longer ultra races, the best way to perfect your training for either discipline is to get out on the trails.
Bikomeye JC, Balza JS, Kwarteng JL, et al (2022) The impact of greenspace or nature-based interventions on cardiovascular health or cancer-related outcomes: A systematic review of experimental studies. PLOS ONE 17:e0276517. https://doi.org/10.1371/journal.pone.0276517
Coates AM, Berard JA, King TJ, Burr JF (2021) Physiological Determinants of Ultramarathon Trail-Running Performance. Int J Sports Physiol Perform 1:1–8. https://doi.org/10.1123/ijspp.2020-0766
Pastor FS, Besson T, Varesco G, et al (2022) Performance Determinants in Trail-Running Races of Different Distances. Int J Sports Physiol Perform 17:844–851. https://doi.org/10.1123/ijspp.2021-0362