Bart Yasso, longtime Runner's World events director, built a following around one of the strangest-looking workouts in distance running: run 800m repeats until your average time in minutes and seconds matches your marathon goal in hours and minutes. Aim for a 3:30 marathon? Run your 800s in 3:30, with equal recovery jogs between them.

It sounds like a party trick disguised as a training method, and for years runners have argued about whether it's real science or a coincidence that happened to catch on.

What it actually measures

Yasso 800s aren't a formula in the way the Riegel model is — there's no published derivation, no peer-reviewed paper behind it. It's closer to a rule of thumb that Yasso noticed held up across a lot of runners he coached: your 800m repeat pace, run to a specific structure, tends to land close to your eventual marathon finish time.

That's the catch — "run to a specific structure" is doing a lot of work. The workout is usually 10 x 800m at goal pace with equal-time recovery, built up to over a training cycle, not attempted cold. Run it as a one-off speed session without the buildup and the correlation falls apart.

Where it holds up, where it doesn't

For runners in the 3:00-4:30 marathon range with a standard buildup, Yasso 800s tend to track reasonably close to actual results — often within a few minutes either direction. Outside that range, and especially for very fast marathoners (sub-2:30) or first-timers without a base, the correlation gets shakier. It also says nothing about fueling, pacing discipline, or the back half of the marathon, all of which matter more than any predictor.

Worked example: Goal marathon of 3:45. Yasso says: run 10 x 800m in 3:45 each, with a 3:45 jog recovery between reps, as your set builds over several weeks. If you can hold that at the end of a build cycle, you're in the range of being ready for a 3:45 attempt — not guaranteed, but plausible.

How to use it without overreading it

Treat Yasso 800s as one data point among several, not a verdict. Cross-check it against a recent race result run through the Riegel Race Predictor or against your training paces from a VDOT-based calculation. If the numbers roughly agree, you've got a decent read on your fitness. If they're wildly apart, trust the race result over the track workout — actual racing under real fatigue tells you more than any repeat session, however cleverly designed.

Run the numbers yourself: Yasso 800s Calculator.