I once met a very good runner who trained by time and overall feeling vs distance run(miles run). In other words, he would take off on a run in one direction or on a trail and his goal would be to run for a certain amount of time rather than a certain amount of miles. Now, with this said, we all know we must run a certain amount of miles when training for a particular distance.
However, there are some days that I prefer to just run for say 50 minutes in the morning and 60 in the eve. I do not have an accurate assessment of miles or distance run, but run according to how my body feels and simply run for an hr, etc.
Upon the conclusion of the run, I am satisfied simply because I have put in the time I planned to keep my legs moving faster than normal.
I am not looking for a definitive answer here but rather some thoughts/opinions on this matter.