The ability to run hard, often, is a very important requirement for the modern footballer.
Over the last number of years, as the time I can give to training has become less and less, I've always found myself returning to 4 minute repeats.
It would generally consist of the following workout
Run for 4 minutes at 90-95% of your max
Rest for 4 minutes( Walking)
Repeat for 4 sets in total
I never thought too much about the science involved, but I always felt that it was a tough session, both physically and mentally. My goal was always to keep the distance covered the same, which is impossible if you start the first set at the right pace.
I came across this presentation by renowned exercise-physiologist, Dr. Jan Hoff, where he talks about "the Norwegian Method". He has worked with Barcelona, Real Madrid, Celtic and many others. It turns out that the 4 X 4 Repeats, are one of the most effective methods in the world for improving cardiovascular capacity.
If you want to go straight to the good stuff, go to 8min 40 into the session.