Have a hypothesis that the usual traintraining advice doesn't work for people with relatively terrible aerobic development. Good development would be someone who's 5k pace is 7min/mile and easy pace is 9min/mile. Bad would be 7 versus 14. Or even 10 versus 16.

Supposely everyone is should do 80% of training at easy pace. One size fits all. But if you're easy is way slower than your hard the two just don't work off each other. The movement is too dissimilar. The ROM too different. Such people instead should do their "easy" at most 3 min/mile slower and make it easy by turning it into intervals. Like 11min/miles with run 4 min, walk 2. Until they eventually build up some aerobic ability.

3/4s are best. Though mentally hard to stick with. All that rest means running very hard. Hard to do for long. 3/3s and 3/2s are next best. Then 2/4s, 2/3s, 2/2s, and 2/1s.

I had been trying to just do steady state easy runs. I'm so slow this way. And don't enjoy it. I like being faster. I like alternating back and forth. I'm sorry but going back to intervals. I'd be very happy to get back to my slow times of previous years. 8.41 for 12, 7.53 for 8, 7.25 for 5, 6.59 for 3. My mileage was actually quite low all those times. 20 to 40mpw.

I worry about injury. But I don't have to go so fast.

The best training for fast endurance running: 2/4's (2 minutes running / 4 minutes walking or very slow jogging) > 3/4's > 4/4's > 2/2's > 3/2's > 3/1's > 3/0.5's > 3/0.1's... (And 1 minute runs are anerobic and for the most part you'd be better off just doing continous longer runs instead. Although if your rest period gets well under a minute, you may start getting some benefit from 1 minute runs beyond a finishing kick.)

Basically run just long enough that it's mainly aerobic. And rest long enough that you're as close to completely recuperated as you've got the time to get.

The whole point of intervals is to spend more time running at or faster than race pace while still running aerobically. Shorter than 2 minutes and the running becomes primarily anerobic. Longer rest periods mean more time spent running faster, (provided you have the time for a longer workout). Furthermore no matter how good a shape you're in, the aerobic system takes longer to recuperate, thus as your running intervals get longer, you really need much longer rest periods to ensure each successive run is still at a good fast pace.

Otherwise, what's the point of even bothering doing intervals? Why do them in a way where you do less fast aerobic running?

And 2/2's > 3/2's > 4/2's etc, etc because provided it's still somewhat aerobic, faster running is just better. As you slow down your stride changes such that you're not even exercising all the muscles that you would need in order to run fast.

Short very fast runs with plenty of rest in between. That's how you should actually do intervals. The limiting factors are how much time you have and how much your joints can handle. (And how tired you are from inadequate recovery from your "recovery" runs.)

pro-plodding along
http://www.time-to-run.com/training/methods/intervals/intensity.htm

pro-interval
http://www.dragondoor.com/articles/endurance-training-intervals-vs-long-slow/steady-distance/

http://www.ultralegends.com/interval-versus-tempo-training/

http://blog.nutribodies.com/15/interval-training-for-improved-sports-performance

http://www.jeffgalloway.com/

http://mikesworkout.blogspot.com/2009/09/interval-training-vs-long-slow-part-1.html

http://www.pponline.co.uk/encyc/0004.htm
But then why the unsupported assertion slapped on the end to only spend 10% on intervals??