Most runners are somewhat familiar with the term Yasso 800’s, a workout that supposedly predicts marathon finishing time from a session of 10 x 800 meters with equal time rest between each 800.

However, as a running coach and marathoner myself, I have to take issue with this workout for two reasons. First. we have no actual evidence to support there is an actual connection between the fitness this workout demonstrates and marathon finishing time – it’s merely a coincidence. Second, the specific demands of this workout do not accurately target marathon fitness – you can run workouts that will provide a greater benefit to your marathon training. Let’s examine those two thoughts in more depth.

Yasso 800’s – Correlation vs. Causation

I’ve met Bart Yasso and had the pleasure of speaking to him in-depth about the “Yasso 800’s”. What I found interesting was the reasoning behind his prediction model of Yasso 800’s and marathon finishing time. Specifically, there was no scientific data that showed, physiologically, why the Yasso 800’s would be a predictor of your marathon time. Instead, Bart simply noticed that there was a correlation between marathon finishing time and the average 800 meter splits when performing a workout of 10 x 800 meters.

It is important to remember that correlation and causation are two different things and that one does not cause the other. This is the basis behind all quantitative research methods. For example, one study demonstrated that that the total US highway fatality rate perfectly correlates to the number of fresh lemons imported from Mexico (full study here). Does this mean that the number of lemons imported from Mexico is causing highway fatalities? I doubt it, but there is certainly an unbelievable correlation.

The outrageous lemon story is good example of why you shouldn’t base your training off correlations. You certainly wouldn’t bet money that lowering the total number of lemon imports would reduce highway fatalities, just like you shouldn’t bet all the hard work you’re putting into your training on a correlation between one workout and your supposed marathon fitness.

Yasso 800’s predict a time that is about 5 minutes too fast

In my own experience, both from my own training and the hundreds of runners who I’ve coached, this workout usually predicts a marathon finishing time about 5 minutes too fast. My theory is that because most runners do not have a strong aerobic background accumulated from years of running higher mileage, their aerobic endurance lags behind their maximum speed. For example, most 4 hour marathoners could run one lap around a 400 meter track in 90 seconds, but very few could run a 6 minute mile (4 x 90 seconds). Many runners simply lack the endurance to maintain that pace for a whole mile.

An 800 meter interval is short enough that you can gut through the session, which relies more on basic speed than an endurance based background. With an equal rest, this becomes much more a test of speed than marathon potential.

Finally, one of the reasons the marathon is such a difficult race is theissue of fuel – the total amount of carbohydrates you can store and the efficiency at which your body uses your available provisions. Accurately predicting a marathon finishing time needs to take this variable into account. Yasso 800’s do not factor in the important issue of fuel utilization in the marathon because it never tests your ability to store and conserve carbohydrates when running.

Yasso 800’s – Not a Marathon Specific Workout

A successful marathon training plan should almost always focus the majority of the workouts on physiological progression and adaptation. Specifically, how a particular workout addresses the physiological challenges of a race and trains you to conquer that challenge.

As Coach Nate Jenkins demonstrated with his 2007 Olympic Trials training, the key to marathon training is focusing on marathon specific workouts, especially in the latter stages of your training. As Coach Nate describes it, a marathon specific workout is a run where the main body of work is run at 95 to 105% of marathon pace. You may do other work within the workout to tire yourself out or soften your body up for the marathon pace work. but the focus of the workouts should be to teach your body to run for a long time at your goal pace and to teach your body to run at your goal pace when you are very tired and have very little glycogen left in your system.

Unfortunately, Yasso 800’s are a VO2 max workout – you run at max speed for 2-4 minutes and then take an equal amount of rest between intervals. Research demonstrates that an increase in VO2max does not increase fuel efficiency. Likewise, VO2 max intervals don’t specifically develop or improve your aerobic threshold. Therefore, a workout like Yasso 800’s during marathon training has limited benefit to your marathon specific fitness.

So do Yasso 800’s have any benefit to your marathon training?

That’s not to say that VO2 max workouts don’t have their limited place in marathon training. VO2 max workouts do increase your overall running fitness and they improve the speed at which you can run, which would in turn make running at marathon pace feel “easier”. However, given many runners perform Yasso 800’s three to four times in their marathon training cycle to “measure” progress, the focus of the training can sometimes become too centered around improving your VO2max, and not focused enough on improving your aerobic endurance and fuel efficiency.

In many cases, you have a short 12 to 16 week window of specific marathon training. This means you have a limited number of workout days upon which you can improve your marathon specific fitness and train to run your best on race day. In my opinion, squandering three or four workouts to gauge your potential based on a loosely correlated predication workout isn’t the most effective way to train.

Finally, I am not suggesting that a session of Yasso 800’s won’t come close to predicting your marathon finishing time – it often does work. However, as a runner and a coach, if I am dedicating so much time and energy to one specific race, I don’t want to leave my training and racing to a mere coincidence. Moreover, why “waste” a workout day when you can run a training session that will provide a much greater bang for your buck.

A Better Marathon Prediction Workout

If you want to test your marathon potential, try a fast finish long run. Head out for a 16 to 20 mile run where you run the last 6-10 miles at your goal marathon pace or a little faster. The demands on your aerobic endurance and specific ability to run fast for a long period of time are better tested than during a session of 10 x 800 meters. With a fast finish long run, you’ll more accurately determine whether you have the strength and endurance to race well, and you’ll be getting in a workout that improves your fitness to a greater extent.

What are your thoughts? Have you used the Yasso 800’s in your training and found them to work well? We would love to hear your experiences with this workout.