I’ve heard some intriguing predictors of a marathon performance. But one is of particular interest. It is said that to predict your marathon time go out and run 10/800m with 2 mins rest between. If you average 3:05/800m then your predicted marathon time would be 3hr 5min. Any validity to this?
3:45
Yasso 800s. Google it.
Any validity to this?
no
what you're referring to is "Yasso's" 10 x 800 with equal time rest (not 2:00)
OK workout, not an accurate predictor
It works better as a negative predictor than a positive predictor. If you're planning to run 3:05 in the marathon, and you can't average 3:05/800m, then you probably won't be able to meet your goal.
But it doesn't indicate anything about your overall marathon preparedness. If you were training for a 5K, you would be able to run 3:05/800m easily, but if your long run was only 12 miles, it's very likely you'd hit the wall in the marathon and not be able to run 3:05. If your overall marathon training, mileage, long runs, etc. have been going well, then you can feel much more confident about your 3:05.
On a normally scheduled hard day about 3-4 weeks before the race go out and run 26.2k on a similar style course at marathon pace.
On race day, well tapered, you will be able to do the 26.2 miles at this pace.