so I'm training to run 8:40 in the 3 km and one of my main workouts is a hard 20 km long run. I usually do these around 6 min mile pace. I've heard of the Japanese doings 2 hard long runs in a row, it was apart of a hard push for aerobic fitness. Has anyone heard of this? Has anyone did this or see/heard of someone doing this? Is this only beneficial for marathon training? what are some really good long run workouts?