I'd like to clarify a point about stamina training. I have been told by coaches that they do stamina work because they have their runner doing workouts like 6 x 800m. I ask about the pace, the 800m runners times over 1500, 3000, 5000, and 10000m, and I find out the reps at 5000m to 3000m pace. On the surface many people might think this is stamina work because the intervals/reps are fairly long for an 800m runner. I don't see it that way. I think slower paced reps, more of them, develop stamina better. It's why I use CV pace as a guide. I know that CV pace develops stamina to a very high level for all runners, even middle distance runners. CV pace is set at 90% of Vo2 max, which I believe is ideal for developing the aerobic capacity of fast (intermediate) fibers (type IIa). In my schemata of training, the type IIa fibers are the most important for track racing distances.
To demonstrate my idea; let me give an example of what I do not consider good stamina training:
Runner's performance time: 4:01 in the 1500m (about 4:20 in the mile); 8:50 in the 3000m; 15:40 in the 5000m.
(This runner has more speed than stamina, as the trend toward a lower performance level appears as the race-distance lengthens.)
80 miles per week: two runs per day, most days; including distance runs at 7:00-6:15 per mile, 600s to 1200's at 5000-3000m pace, or 1500-800m race-pace reps on the track.
Yet, despite the volume of training, 5k-3km paced reps, this runners' 3000m time is on a lower performance level than his/her 1500m time. And, to illustrate the point further; this runner's 5000m time is on a lower performance level than his/her 3000m time. It's a trend that show this runner's stamina is poor. That is, this runner probably has good speed and a strong VO2 max, but they are lacking in stamina, so they are not holding a high percentage of their VO2 max during races.
The problem is most runner hit a ceiling in the speed quickly and their Vo2 max a little less quickly, so further training in these areas produces less and less improvement. Continuing to train the above runner with heavy doses of speed and VO2 max will not make them improve over the 1500m race-distance - their specialty - after 2-3 years. Even running 80 miles per week won't help them get off the 4:01 plateau.
How is the problem solved? In my opinion; stamina training is the solution. I would prescribe slower paced, long intervals @ CV to 15km pace, progressive tempo runs over hills, and long distance runs with the pace increasing as fatigue sets in.
Note this strategy is (more or less) akin to the Lydiard philosophy of regularly performing plenty of long distance running at a good/strong aerobic pace. The goal, I think, of Lydiard's focus is developing stamina; to expand a runner's ability to hold a high fraction of their peak speed longer.