I think one part of running that hasn't been studied enough is the use of walk breaks. A few weeks ago, this New York Times article generated a lot of discussion about the subject. Some people felt that taking a walk break during a race was not appropriate for "real runners". Others commented on how they have effectively used walk breaks to complete marathons and stay injury-free.
From a strictly racing point of view, walk breaks would not help an elite runner, except for maybe walking though a water station. I don't see the Kenyans taking time to walk and recover during a race. What I'm more interested in is the health aspect. Is running with walk breaks healthier than continous running?
Based on the evidence available, I would have to say yes. If you read accounts of hunter-gatherers on the hunt, they often stop for walk breaks or to check the trail. Also, you can look at the ultra-runners on trails who stop to walk up steep hills. In the book, "Born to Run", the author discusses how the Tarahumara Indians often choose to walk instead of run up a steep hill.
The underlying key here is energy expenditure. If a hunter is on an endurance hunt, only a moderate overall pace is needed to keep up with the prey. Why risk exhaustion by running up steep hills if walking will still keep you in the chase?
In addition, here is a new study I found related to this. Subjects performed either a low-intensity continuous run or a moderate-intensity intermittent run, both for 90 minutes over the same distance. It turns out that the continuous run raised LDL "bad" cholesterol, while the intermittent run raised the HDL "good" cholesterol. No matter what one thinks of the cholesterol theory, it certainly looks like the intermittent protocol was superior in this regard.