Yasso 800s, named after the runner who invented them, Bart Yasso, are both a for of Interval Training and a fitness test.
2 The Protocol
Yasso 800s require you to run intervals of 800 meters (half mile) with a recovery of the same time as the interval took. Each interval should be run close to the same time as all the others. You need to run 10 of the intervals for the prediction to be valid.
3 The Prediction
The time you ran the intervals in minutes and seconds is a predictor of your marathon time in hours and minutes. So if you ran the intervals in 3 minutes 18 seconds, 3:18 (6:36 pace) the predicted marathon time would be 3 hours, 18 minutes.
4 How it works
The best predictor of how fast you can run a race of a given distance is how fast you can run a race of a different distance. This prediction combines your aerobic capacity and your efficiency. The Yasso 800s are using the same approach, but based on a very short distance.
5 Limitations of the prediction
This prediction is showing what your aerobic capacity and efficiency indicate your potential performance would be at the marathon distance. It does not give any indication of your endurance, so results can vary widely. If you have focused your training on the marathon distance, then the Yasso 800s can be a useful predictor. A more effective predictor is to use a shorter race with the VDOT Calculator.