4 Factors That Determine Ultramarathon Performance 

These four physiological elements have shown scientific links to better performance in races 50K and over.

Photo: Getty Images

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Whether you’ve been running ultramarathons for a while or you’re just getting into the trail scene, at some point, you’ve probably thought about the million-dollar question: 

What determines how well we perform in an ultramarathon? 

Compared to road running, where paces tend to align across similar courses and more controlled conditions, ultramarathons are a puzzle. Does performance come down to our fitness level, training volume, or climbing ability? Or is it mental training or fueling strategy? 

A 2021 study in the International Journal of Sports Physiology and Performance aimed to uncover the physiological factors involved in ultra performance. Researchers looked at race day performances among runners across distances including 50K, 80K, and 160K, then correlated those results with various factors that the athletes had measured on race day. 

The research team found that in the 50K, higher levels of training volume, cardiovascular health, and aerobic fitness were all related to better performance. Non-finishers completed fewer weekly training miles compared to finishers (average of about 32 miles in the several weeks beforehand, versus 48 miles for finishers) and a lower weekly running distance over the previous year (average of about 20 miles/week, versus 36 miles/week for finishers).

Peak velocity achieved in a VO2 max test and baseline blood pressure were the top performance predictors for the men’s 50K, and VO2 max results were also one of the best predictors for women. 

Here’s how you can measure and maximize each of those factors in your own training and performance. 

Training Volume 

For distances from 5K to half marathon, 15-25 miles a week might cut it. But once you start looking into ultras, 30-40 miles a week or more makes a marked difference in performance. But more isn’t always better and can result in diminishing returns or even injury, especially if increased too quickly. The amount of time spent training has a bigger impact than overall mileage, especially as you train on hillier, mountainous terrain, where you’ll cover fewer miles in the same amount of time.

If you’ve been running 20-25 miles a week or less and you are eyeing a 50K, consider upping volume over time. If you hit consistent 50-60 mile weeks and aren’t seeing much improvement, that extra 5-mile shakeout might not be doing you any favors. To figure out how much mileage you should run, take a look at this article.

Cardiovascular Health 

If there’s one thing most endurance runners don’t need to worry about, it’s cardiovascular health (unless we’re talking about the dangers of too much running on our heart, or monitoring arrhythmic heart beats – both serious conditions that should be addressed). There is no doubt that consistent, regular aerobic activity, especially at lower intensities, improves cardiovascular function. 

However, runners can be prone to particularly low heart rates, and overdoing it can do some damage; namely, thicker heart walls and scarring of the heart, when done without enough recovery in between long, hard efforts. Monitoring your heart rate (both resting and during activity) can be helpful, and be sure to discuss any significant changes with your doctor.

Aerobic Fitness

Ah, aerobic fitness – you can’t read a training article these days without hearing about it. Considering that ultramarathons rely vastly more on our aerobic systems than our anaerobic systems, it’s no surprise that endurance is your friend. Building your base is probably the most important factor to ultra training, along with volume. Thankfully, the two go hand-in-hand. For a reliable base-building plan, look no further than our 10-week program.

VO2 Max Test Performance

Also referred to as “peak velocity” or “peak oxygen uptake,” VO2 max measures the maximum amount of oxygen your body can utilize during exercise. While some of our VO2 is predetermined or hereditary, there is room to improve this number within our training – and for the benefit of our endurance. This one may surprise ultramarathon runners, especially those of us who prefer long, slow distance to speedwork. Before you become a stranger to speed, remember that by sprinkling just a few (1-3) faster sessions into your week, you can give your peak velocity score a major boost. Mix in tempos, hill repeats, and interval sessions to keep things interesting.

For more ideas to rev up that engine, check out these 5 speed workouts.


To perform well, assess your training volume, monitor your cardiovascular health, work on aerobic fitness, and don’t forget speedwork. These four indicators, when managed through training, can turn into big gains on race day. A smart training plan will incorporate slow builds in mileage, roughly 80-90% of it at or below aerobic effort with a sprinkling of speedwork, and ample amount of rest to care for your heart health.

You may be wondering: what happens when you go beyond 50K? In the study above, peak velocity in the VO2 max test was the only notable determinant of performance for the 80K distance. Up to 100 miles, there were no direct determinants, which begs the question: in the longest of races, is mental strength more important than physical strength? Perhaps physiology only goes so far. More research might be necessary when it comes to the longest ultras.

Other indicators noted in the study included baseline blood pressure (particularly for men) and “loss of body mass.” The inclusion of blood pressure could be due to the fact that with increases in aerobic fitness and cardiovascular health often comes a correlating blood pressure drop. 

Loss of body mass, on the other hand, could be a dangerous metric to use as a performance indicator. Focusing solely on reducing body mass is a surefire way to put you at a greater risk for injury and long-term health consequences (such as RED-S). It’ll likely suck the fun out of trail running, too. Loss in body mass may be a byproduct of training hard or making lifestyle changes (working with a dietitian or under the care of a physician), but it can easily become a slippery slope. Focusing on training- and recovery-related metrics will be best for those of us who want to run long, healthy, and happy.

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