In surveys, I've found that those who used to run 20 miles (as a longest long run), andbump the distance up to 26 miles, experience an average improvement of over 15 minutes.
This is all very well, but the physicist comes along and shows that you never bump into anything: even when you run your head against a stone wall, you do not really touch it.
Long long ago in the State of Song, there was a farmer who used to go to the fields to work everyday. One day he saw a hare run in panic andbump against a tree. He went up and found it dead.