This plan is for the experienced marathoner who routinely trains 6 days a week and up to 60-75 miles a week.This plan is focused on 6 runs a week and you could add a 7th if that is what you normally do. The threshold workouts should be done on flat ground. I have given the option of 7 runs over 20 miles and you can do less then that if you want but based on this weekly mileage range I would say aim for at least 5. You should have at least 4 weeks of base training under you before starting ...