Why Ultrarunners Should Sprint

When I trained for my first ultramarathon (the American River 50 Mile Endurance Run) over the winter of 2015-16, I had an Achilles tendon injury that prevented me from doing any training that was faster than marathon pace, give or take. Fortunately, I had no limitations on how far I could run, and took full advantage of this freedom by completing individual training runs of up to 37 miles.

When I arrived at the start line of AMR50 on April 2nd, I was definitely fit, but not as fit as I would like to have been. A crucial piece was missing; my legs felt the lack of faster running in a way that’s hard to define. This feeling was validated not only by the ensuing race, in which my performance was humdrum, but in my next ultra, which I won following an injury-free buildup that including regular doses of moderate- and high-intensity work.

Many ultrarunners voluntarily eschew such work, having little taste for it and assuming it makes no significant contribution to success in low-intensity races that require many hours to complete. But a recent study says otherwise, further validating my experiential sense that fast running is a vital component of effective ultramarathon training.

Conducted by Spanish scientists and published in the European Journal of Sport Science, the study involved 20 “ultra-endurance runners” with an average age of 40 years. For 12 weeks, half of these subjects followed a “threshold” training program in which two-thirds of total training time was spent at low intensity and the remaining one-third at moderate intensity (i.e., roughly lactate threshold intensity), while the other half followed a “polarized” training program with an equal overall workload but in which 80 percent of total training time was spent at low intensity and 20 percent at high intensity. Both groups lost body fat during the 12-week training period, but only the polarized group showed improvements in running economy and in running time to exhaustion.

Do we conclude from these findings that ultrarunners should never do any training at moderate intensity? Of course not. The purpose of the study was to compare the contributions of moderate- and high-intensity running to fitness development within the context of a mostly low-intensity training program, not to identify the optimal way to train for ultramarathons in the real world. But what we can conclude from the study is that ultrarunners should do a significant amount of training at high intensity.

If this finding seems counterintuitive to you, it’s probably because you don’t fully understand how high-intensity training works. The purpose of doing fast workouts is not, in fact, to get faster. Rather, it is to enable you to use more of the speed you already have in races, regardless of distance. High-intensity running does this in a variety of ways, including by increasing aerobic capacity, improving running economy, and even elevating pain tolerance. You only have one body, and it is this one body that is altered by any sort of training you do. Thus, even though a set of hard intervals on the track doesn’t look much like a 100-kilometer trail run, it will help you perform better in such a race by altering your body in beneficial ways that complement the benefits of longer, slower training runs.

This is why the 80/20 ultramarathon plans that I’ve just created for TrainingPeaks include speed work—not a ton, to be sure, but enough to give you better results than you would get from a training plan that did not require you to test your higher gears. There are eight plans in total: four levels each for 50 miles/100K and for 100 miles. Check ‘em out!