Can you predict your half marathon time with this workout?

You may be very familiar with Yasso 800s training. Designed by former Runner’s World journalist Bart Jasso, his goal was to give an accurate forecast of your marathon time based on a relatively simple treadmill workout. You’re running 10 x 800 meters, and your time in minutes per repetition should match your time in marathon hours.

For example, if you ran 800 meters in 3 minutes 30 seconds, you can run a marathon in 3 hours 30 minutes. The time between repetitions should be the same as the repetition time (in the above case 3 minutes 30 seconds). This is by no means a perfect formula. Many commentators believe that it is entirely possible to run a Jasso 800 session but not run the corresponding marathon time. Coaches also note that the preparation and ability to run well at middle distances is very different from the requirements needed to achieve a marathon time. But despite this, the Jasso 800 remains a classic workout – and may now be the equivalent of a half marathon.

This runner was dubbed the “Fultzy 400s” by the legendary running writer and marathoner. Amby Burfootin honor of 1976 Boston Marathon winner Jack Fultz. The workout involves running 20 x 400 meters with 60-90 seconds of walking rest between repetitions. If you’re planning on running a 1 hour 45 minute half marathon, your goal is to run the reps in 1 minute 45 seconds. If you want a half marathon of 1 hour 30 minutes, do the reps in 1 minute 30 seconds. You get the idea.

But is it really an accurate predictor of half marathon times? Former elite marathon runner and running coach Joe Wilkinson not so sure. “I think it’s hard to extrapolate race predictions based on just one session,” she says. “It’s always an attractive idea. But the best indicator of competition results is the training as a whole.”

“I think the difficulty of the Yasso 800 compared to the Fultzy 400 is that the pace at which you will be running a Fultzy session is significantly more difficult. From a physiological perspective, Jasso’s formula corresponds to a threshold pace that better predicts marathon (and half-marathon) times. This formula, on the other hand, has you running at a speed close to your running pace. VO2 max (or even higher depending on your HM time) which is much faster.’

“There is some correlation between VO2 max and pace at VO2 max and half marathon time. But there is much less correlation than between the threshold and the marathon. Moreover, it is a very hard workout.”

“So I wouldn’t recommend basing your half marathon pace on this session because the pace is quite hard. However, if you do well in this session, you’ll probably be in great shape – and maybe you should reconsider your ambitions too.”

Regardless of whether either workout can actually accurately predict your race time, it’s certainly a case that they’re both great workouts in their own right, and as long as the day isn’t too close to race day, they’re definitely worth trying .

Rick Pearson is senior editor of Runner’s World UK. He’s been with the brand since 2017 and loves testing PB-compatible shoes for on- and off-road use. Rick is a marathon runner for less than three years, and sometimes likes to remind people of this on the Runner’s World podcast, which he co-hosts. He once ran a steam locomotive over 14 miles (he won narrowly) and a marathon on a horse (he lost comfortably).