One of the things I don't see discussed enough in terms of interval training is the quality of each interval. For example, if you go out and run some intervals, which one is the more beneficial - the first or the last?
The first interval provides the most benefit, and there are probably diminishing returns after that. In fact, I've wondered how few intervals you can perform and still get the majority of the benefits. Tonight I was pretty tight on time, so I just walked and threw in a couple of short intervals (~ 100 meters) during the walk.
If a person is trying to get into shape, I bet a couple of intervals interspersed with low-intensity work could dramatically improve fitness compared to only low-intensity work.
