Originally Posted by Allen Yeh
What is the goal for doing the sprints to begin with?
That will dictate your work/rest ratio.
This is what I was trying to get at earlier.
If the goal is sprinting improvement, you need to consider going very close to (if not all the way to) full recovery, which for most people is about 1 minute per 10m sprinted, so 4 minutes to recover from a 40.
If the goal is fat loss, I would still argue (if you have the time) that you should go the full recovery route as well, because you'll get the fat loss benefit and the sprint improvement benefit as well.
If the goal is conditioning, then either of the intervals you suggested should work OK, although it would depend on what you're trying to condition for. Different times/distances for rugby vs. trying to improve your kick at the end of a 10K.