This BBC article on High Intensity Training (HIT) looks interesting.

http://www.bbc.co.uk/news/health-17177251

Although it appears that it can have an effect on the health of some people it probably wouldn't help greatly the fitness of someone who is already at least moderately fit. (Forumites.)

The following article discusses using HIT for training increases the interval times.

http://well.blogs.nytimes.com/2012/0...raining&st=cse

I was wondering how many people fit some sort of high intensity interval training into their training regime.