I was introduced to the concept of "Extreme Stretching" via John Parillo during the 80s and it has been a core concept for me ever since. Basically, it consists of stretching the fascia / connective tissue beyond its previous limits while the muscle is pumped. Parillo called it "fascia stretching" and he also advocated "fascial planing" which is a form of "extreme massage" where the muscle is very forcefully "planed" with the heel of the palm, again, while pumped.

Every muscle is made up of thousands of muscle fibers. These muscle fibers are all individually wrapped with a connective tissue wrapping, or a sheath. This is called the endomysium. These individual muscle fibers are then organized in bundles( called fascicles ) which are covered by another connective tissue sheathe called the perimysium. These bundles or fascicles are then placed together in an orderly arrangement( which determines the shape and functionality of the muscle ) and held in place by a layer of connective tissue known as the epimysium. Finally each of these layers is held together by the deep fascia (a coarser material). The connective tissue of every muscle fiber acts like a girdle of sorts. Which means that it binds a muscle group together, and to its neighboring muscle in many cases. It also protects, organizes and allows the force of contraction generated by the thousands of muscle fibers in a particular group, to be harnessed with great efficiency!

Parillo's idea was that if you were no longer fighting the restrictions of tight, unpliable fascia, but rather a more elastic and pre-expanded connective tissue, then you would have more room to grow. Now before that, there was a woman named Dr. Ida P. Rolf. She invented a famous technique called rolfing. It is a special, extreme form of massage that as Ida puts it, manipulates deep tissue. She theorized that you could move around, loosen, expand, realign and strengthen this tissue with her great techniques! Interestingly enough, her techniques can not only drastically enhance muscle growth, but also increase separation between muscle groups.

This also ties into possibly explaining so-called "muscle memory" and a possible benefit of site enhancement injections.

But what is Mechano Growth Factor, and what does extreme stretching / massage have to do with it?

Mechano Growth Factor (MGF) also known as IGF-1Ec is a growth factor/repair factor that is derived from exercised or damaged muscle tissue. MGF has been shown to boost muscle mass by improving the ability of wasted tissue to grow and improve itself by activating muscle stem cells and increasing the upregulation of protein synthesis. MGF is a part of the IGF family, but, in the case of MGF, this part of the peptide acts as a separate growth factor involved in initiating muscle satellite (stem) cell activation in addition to its IGF-Ireceptor domain which increases protein synthesis, and hence improves muscle mass.

Muscle is a post-mitotic tissue and as cell replacement is not a means of tissue repair there has to be an efficient local repair mechanism otherwise the damaged cells undergo cell death. The extra nuclei for muscle repair and hypertrophy are provided by the muscle satellite (stem) cells. The pool of these stem cells is apparently replenished by the action of MGF, which is produced as a pulse following a mechanical challenge.

The impetus for this is the negative / stretch component of the exercise. Thus, extreme stretching / massage induces the MGF / satellite cell activation as well as protein synthesis.

Now since MGF is dependent upon iGF, which is dependent upon hGH, the ability to produce MGF declines with age, and this is commensurate with the decline in circulating GH levels. In fact, loss of muscle mass in old age is associated with an impaired ability to express MGF. But if you are relatively young and/or using exogenous hGH, you may find extreme stretching very useful for size gains, as well as increasing separation between muscle groups.

So I believe the benefits of ES to be two-fold. Expanding the fascia and inducing the expression of MGF.

Here are some examples of various stretches. They can be done after each set, or after the muscle group is completed being trained. These come courtesy of Dante Trudeau, aka Dogg Crapp, (from his user on Animal's board, back in the day) who also advocates Parillo's ES. Obviously adjust the weights you use appropriately.

Chest

Flat bench 90lb dumbbells chest high--lungs full of air--first 10 seconds
drop down into deepest stretch and then next 50 seconds really push the
stretch (this really, really hurts) but do it faithfully and come back and
post in 4 weeks and tell me if your chest isn't much
fuller and rounder

Triceps

Seated on a flat bench, 75lb dumbbell in my
hand behind my head (like in an overhead dumbbell extension)--sink dumbbell
down into position for the first 10 seconds and then an agonizing 50 seconds
slightly leaning back and pushing the dumbbell down with the back of my head

Shoulders

This one is tough to describe--put barbell in squat rack shoulder
height--face away from it and reach back and grab it palms up (hands on
bottom of bar)---walk yourself outward until you are on your heels and the
stretch gets painful--then roll your shoulders downward and hold for 60
seconds

Biceps

Just like the above position but hold barbell palms down now (hands on top of
bar)--sink down in a squatting position first and if you can hack it into a
kneeling position and then if you can hack that sink your butt down--60
seconds--I cannot make it 60 seconds-- I get to about 45—it’s too painful--if
you can make it 60 seconds you are either inhuman or you need to raise the
bar up another rung

Back

Honestly for about 3 years my training partner and I would hang a 100lb
dumbbell from our waist and hung on the widest chinup bar (with wrist straps)
to see who could get closest to 3 minutes--I never made it--I think 2 minutes
27 seconds was my record--but my back width is by far my best body part--I
pull on a doorknob or stationary equipment with a rounded back now and it’s
way too hard too explain here--just try it and get your feel for it

Hamstrings

Either leg up on a high barbell holding my toe and trying to force my leg
straight with my free hand for an excruciating painful 60 seconds

Quads

Facing a barbell in a power rack about hip high --grip it and simultaneously
sink down and throw your knees under the barbell and do a sissy squat
underneath it while going up on your toes. Then straighten your arms and lean
as far back as you can---60 seconds and if this one doesn't make you hate my
guts and bring tears to your eyes nothing will---do this one faithfully and
tell me in 4 weeks if your quads don’t look a lot different than they used to

Calves

I don’t need to stretch calves after because when I do
calves I explode on the positive and take 5 seconds to get back to full
stretch and then 15 seconds at the very bottom "one one thousand, two one
thousand, three one thousand etc" --15 seconds stretching at the bottom
thinking and trying to flex my toes toward my shin--it is absolutely
unbearable and you will most likely be shaking and want to give up at about 7
reps (I always go for 12reps with maximum weights)--do this on a hack squat
or a leg press--my calves have finally taken off due to this and caught up to
the rest of me thank God.

These are excellent examples that will increase your mass by leaps and bounds! Take a look at Arnold Schwarzenegger's pecs. He would get the pump of his lifetime and then stretch his pectorals using dumbbell flys held in the lower position of the movement just as I am suggesting you to do! The Oak could actually touch the floor with his arms, and he arguably has the best chest in the history of the sport and certainly the most effective! Tom Platz stretched his quads like mad, and no one argues the fact that he had some of the freakiest quads in the history of the sport!