I just finished a 10.012km run that lasted about 0hh:47mm:46ss !
Today I decided to do a type of run that I never did in the past. I didn't have much time so I just did 10K but you can do it with more kilometers.
I ran 10 km in total but with a fast 5K in it. So I did 2.5 km at a slow pace, then 5 km at my top speed on that distance and then again 2.5 km at a slow pace. I started running seriously again two or three weeks ago so I didn't have a big objective. I just knew that I could do it around 20 minutes (but probably a bit more than a bit less than that).
Finally I was happy with my time since I did my 5K in 20'03". It means that I didn't loose much from my best form.
Contrary to what I thought, it is not much harder to do the 5K between two slow runs. It's only difficult for the first minute or two after the fast part of it.
For the record, I found this type of training by following some good runners on Strava. I know one guy who does that once in a while and I wanted to try it.
Check out some detailed info at my EXHAUST page
Join me in testing out EXHAUST!