I'm not sure about that. I have a spreadsheet that calculates my overall run time, based on fast/slow (Fartlek running). If I change the values to only fast, the reduction in time is minor (I only go slow for 30 seconds in every 6 minutes). I've played around with different paces, different times etc.Simon, have you tried a steady pace for the 10km run? I think this would get you better times than the fast - slow technique you are using.
I'd have to try it and see. I'd probably slow down towards the end of my run, so maybe it's swings and roundabouts.
I do this fast/slow system to allow my heart rate to decrease between each fast run - it drops by at least 20 bpm in 30 seconds.
Still, I might give it a go next run.