That last post was kind of quick. The wife was on me to get up and walk the dog.....yeah, I know.
As I see it, the difference between strength and speed endurance (as it is used by most coaches) Strength = Aerobic Endurance or the ability to run at a fast pace for a long time without building up fatigue. As in, that guy's wicked strong, he just threw down a 12 mile tempo in 60 minutes. Speed Endurance = the ability to resist fatigue at much faster paces.
The distance that is most dependant on Speed Endurance is the 400m, with the 800 being a close second. Both events require that the athlete run at close to top speed for a good chunk of time. It is not uncommon for my 400 runners to hit the 200 on a relay split of a 4x4 even with their best 200 time. It is not uncommon for my 800 runners to split the first 400 at a time within a second or 2 of their best 400 time. Speed endurance is the ability to keep going under those circumstances and while aerobic endurance will build a good foundation for speed endurance, aerobic endurance training will never develop the ability to keep going during an 800 when you've almost matched your 400 PR and still have a lap to go.
Workouts to develop speed endurance fall into 2 categories. Both types must be done at mile race pace or faster to have the desired effect.
Type 1: Long reps with long rest. An 800 runner might do 3-4 x 500 @ 800 race pace with full recovery in between. A staple of early season 400 training in many programs is a 600m (600-500-400-300-200-100) breakdown with each rep being very hard. These workouts with long rest are more anaerobic in nature because each rep starts off from a state that is near to resting state. Because the aerobic engine is not running hot at the beginning of each rep, the glycolytic system needs to provide a greater chunk of the total energy for the rep while the HR, stroke volume, and peripheral dilation get adjusted.
Type 2: Short reps with short rest. An 800 runner might do 4 x 5 x 100 @ 800 pace with 30 sec between reps and 3-4 min between sets. A miler might do 16-20 x 200 at mile pace with 30 seconds recovery. This type of workout can also give a strong aerobic stimulus because the HR, stroke volume, and peripheral dilation will stay high through the entire workout.
In longer races, speed endurance gets used at the end, with the caveat that in order for speed endurance to make much of a difference in races longer than 800, the athlete must first have a great deal of aerobic endurance. Despite his superior 400m ability, LaShawn Merrit will never outkick Galen Rupp in a 10k.