I've been looking more into the routines of master sprinters, and what contributes to their leanness across the years. I found some information here, where a few sprinters have posted their weekly routines. What's amazing is that some of these sprinters do no types of endurance work, yet they remain lean.
This led me to think a bit more about sprinting compared to interval training. The two are often lumped together, but they really have two different objectives. Interval training, with its short rest periods between work intervals, is designed to help a person run faster, but the primary application is for distance events. For example, interval training has been shown to improve 5k times.
Pure sprinting work is much different. Here the focus is on brief sprints, with long rest periods in between to fully recharge the muscles.
We know that interval training, such as the Tabata protocol, is effective for burning fat. Yet we also know that sprinters, who may do no interval training or endurance work, are very lean. So which is better for overall health and fat loss?
I think one clue comes from my post about runners gaining weight as they age. They are putting in lots of miles, yet they slowly gain weight. So what's missing? Intensity and the corresponding hormone release.
This is covered more in the nice book, " Ready, Set, Go, Synergy Fitness" by Phil Campbell. Growth hormone production naturally declines with age, and intense exercise is the only way to slow this decline (short of hormone drugs).
When a person performs interval training, they are not going to be exercising at the highest intensity. They will have to lower the intensity a bit if they want to complete all the intervals. I know this from experience when I do the Tabata interval training (20 second sprint, 10 second rest, and repeat 7 times). If I truly go 100% on the first sprint, there's no way I will make it through all 8 sprints without really dragging.
Also, my other thought is that if a person never goes 100%, such as in a short sprint, wouldn't they eventually lose this ability over time? After youth, nature's law is "use it or lose it", and if a person doesn't use their maximum capacity occassionally, it seems likely it would diminish.
Perhaps top sprinters like Maurice Green and Justin Gatlin don't have good endurance. Perhaps they can't even run a mile for all I know. But is this bad? How much endurance is necessary for health? Aerobic exercise has been shown to improve health outcomes, but the type, intensity, and amount necessary are open to debate.
From my readings of hunter-gatherers, their main endurance activity was walking. Perhaps the proper combination of walking and pure sprinting can give the best of both worlds: high-intensity sprinting which releases hormones that burn fat and keep us young, and lots of walking which also burns fat and provides cardiovascular benefits.