If a training program tells you to run say 5 miles one day, what are the consequences of splitting up that run? Is there some gray area where you can reap the same/most benefits (say splitting run to 4 and 1 VS. 5 one-milers)? Studies to show the difference would be great.
If you are marathon training and your run that day is 20 miles, the point is to get used to running that mileage so I would say splitting the run is detrimental to the training. I think there may be some leeway in the lower mileage zones though?