I recently ordered this paper, which turned out to be a very good review of interval training. The review was concerned with which types of interval training elicited the greatest improvements in VO2max, or aerobic capacity.
In order to maximize the effects of interval training, the recommendations are as follows:
The work interval should be between 90% and 105% of VO2max
The work interval should last between 15 and 30 seconds
The relief interval should be between 15 and 30 seconds
Cumulative work interval time should total at least 6 minutes
There should be no break between the warm-up period and the intervals
These are sound recommendations which can be used to build an effective interval training program.