If you do 10x400 what’s the difference in benefit between starting at 70 and ending up at 60 vs. starting at 60 and ending up at 70? Is there any difference in physiological benefit? Other than risking injury by going out hard and not practicing smart pacing.
Yes, running a 60 on fresh legs is easier than running a 60 on tired legs. In either case you're going to have junk in your legs after 8-9x400, so you get way more out of your last few laps if you negative split
There is definitely a difference in the stimulus between starting hard and hanging on v. starting easy and accelerating gradually. I would be interested to hear from knowledgeable coaches or physiologists if they ever actually recommend a workout that starts fast and ends slower. I can't recall ever having a coach prescribe that.
Clearly if you are suffering through the last 9 400s because of a hard first one, the risks outweigh the benefits. And also obvious is the fact that we run interval workouts so that we can run relatively more and more quickly, without straining. So faster on the early reps than you can maintain probably doesn't accomplish that primary goal.