Beating a dead horse is always fun....
so...
in essence, the "eccentric" phase of the contraction is simply most commonly known for activating (possibly) more muscle fibers and, more importantly LENGTHENING the muscle fibers, which in turn, truly, is just a STRETCH
Stretch the living shit outta someone, they are going to be sore the next day, at the insertion points and possibly the origins of the muscle
Give someone a DEEP TISSUE MASSAGE (like that???) If you've never had a REAL true, blue deep tissue massage, you are in for a big surprise. Even if the biotch lays hot presses and cold presses on you afterwards, YOU WILL STILL BE SORE the next day
I can't believe that some people here would actually say "Don't comment unless you know WTF you are talking about"
If bodybuilding and all phases of contraction were TRULY understood by science, we wouldn't need trainers, books, workout programs, rags and who knows what else to try to tell us how to build muscle.
We would have a "one size fits all" program, we would have learned it a long time ago and EVERYBODY would be doing it. Mentzer never would have argued with Arnold about repetitions, or "high-volume' training.
The only way to stretch a muscle is through the eccentric phase of contraction. Point is, you could avoid the eccentric portion, just overload the muscle with time-under-tension, and then stretch the muscle real good after the pump.
You will be sore, most likely.
You could also JUST STRETCH without weights and STILL BE SORE the next day.
So much shit in bodybuilding and fitness is entirely subjective, hence; mags, rags, books, internet and DISCUSSIONS LIKE THIS!
Right? Right.
Do you know that scientists still argue about hyperplasia and hypertrophy? Does that mean anything to anyone? You gonna change up your workout tomorrow?
Now, with all the scientific data processing in the world, why didn't that ugly jackass in Generation Iron win the Mr. O?

I mean, he hooked up diodes and had computers and scientists showing him schematics and electronic data that was supposedly entirely and one hundred percent accurate, and this shit was going on with EVERY repetition. His nutrition was approached the same way, yet he failed miserably and truly appeared to be disappointed? But, but, but.... I wonder if he went back to the lab after his loss and burned it to the ground? Ya know, just like the competitor loser blames his/her coach/trainer when they lose and praises them when they win?
Shall we blame genetics? Or maybe the fact that we just don't know if the Myostatin gene is truly inhibited allowing only those with this genetic predisposition to possibly 'gain muscle and lose fat at the same time'

?
We are just truly ignorant individuals, (myself included), that are grasping at straws when all we really have is empirical data. What works for US!
Yeah, so what if you ripped out Lee Labradas workout in FLEX magazine 20 years ago.... do you now look like him?