For folks that run more than 70 miles a week for marathon training, most of what I have read suggests getting some of that milage in by running two a days, that makes sense. However, what is not clear is how long the runs should be. In the past I have done one day a week with a 6 to 8 mile run in the AM and intervails in the evening. I have seen other articles suggesting that two runs as sort at 30 minutes is good way to get the easy milage in without putting to much stress on the body. What are people's thoughts on how long easy runs should be when doing two a days?