The idea behind this kind of circuit is strength endurance development obviously. What we are trying to do in basic terms is to force fiber recruitment and extend the endurance of those fibers. The exercises serve as a way to increase fiber recruitment, as does the fact that it's done uphill. The sprint at the end is for maximal recruitment of specific fibers. You'll notice that we go from bounding to sprints at the end.
In addition to neuromuscular adaptations, it also serves as an introduction or maintenance of some higher lactate work. If you took lactate readings (I've done it on myself), you'd see that following a circuit, lactate readings are relatively high. Normally when you do a lot of work with high lactate, you effect the lactate threshold because it manipulates the production/elimination ratio. Most of the time when you do high lactate work, it's pretty fast running, so you are essentially shifting to adapt to the higher lactate/high glycolyitic work being done. Your body's pretty smart in the sense that it adapts to what you give it. The fact that fast "anaerobic" work reduces LT is not a problem in some cases (it's all about balance) and at the right time of the season.
However, during a base phase, that's not the time you want to hurt the LT. Well, hill circuits like this allow for high lactate work to be done without it affecting LT. Why? Because it is non specific lactate work. You are using different muscle fibers than normal, and the one's you are forcing to be used are the harder to recruit FT fibers. So, they are used for high anaerobic activities. You are going to be producing most of this lactate from these fibers you normally don't recruit. In addition, the ST fibers are going to be trained to take up and use that lactate.
This is a general circuit, meaning the exercises and running are carried out at about 75-80%. It's important NOT to take this workout without knowing what surrounds it. The workout by itself probably won't do much, but in a larger paradigm it works well.
Before doing this type of work, you need sprints (either flat or hill) to increase the muscle fiber pool (the total fibers that can be recruited). Then you can use general circuits like this to help recruit these fibers during a longer activity.
You combine this work with regular strength endurance work that gets progressively more specific. A good way to work these hill circuits into something more specific is the use of mixed workouts. A workout like 1600,600,1200,500,1000,400 with 3-4min rest, with the paces being at 10k,3k,5k,1mi,5k,1mi takes the hill circuits and translates those adaptations into specifically helping your 5k (in this instance). The longer reps are for specific endurance, while the shorter intervals in between serve to force fiber recruitment and squirt some lactate into the system. Then you go back to the longer intervals to use those fibers, and train them to work under fatigued conditions (enhancing their endurance).
You can also manipulate the circuits to achieve different goals. Increase the speed of the running portion or increase the intensity of the circuits will both bring about different adaptations.
Lastly, for kick development, do a kick workout where you force fiber recruitment under very acidic conditions. A classic example is 300m at 800m pace, 100m bounding, 200m kick in. The 300m serves to build lactate, the 100m bound forces recruitment, the 200m kick in trains recruitment/use of these fibers under heavily fatigued conditions.
Finally, I've written on strength endurance and circuits before, so if you have any questions look there or leave a comment.
Enjoy the Video and thanks to the guys for letting me run along and film them. (NOTE: many of these guys have been doing a progression to this point over 3+years, or at least have a long period of solid mileage, I wouldn't give this to a freshman or a relatively undeveloped runner).