I was thinking about my recent post on sprints, and I wonder if I worded the question wrong. I was concerned about the rest period between sprints, but this should be related to the length of the sprint itself.
I have been reading through this paper that looks at the effects of sprints in more detail. One of the key sentences is:
"Mitochondrial enzyme activity also increases after sprint training, particularly when long sprints or short recovery between short sprints are used as the training stimulus."
This made me think about those recent studies using 30-second sprints. With a longer sprint, the aerobic metabolism will be involved, and endurance did improve with 30-second sprints in the studies. Similarly, a number of shorter sprints with brief rest periods will also train the aerobic metabolism.