To begin with, they do not stay in the muscle for 3 to 5 years. They get dissipated within months. However, during this time, they have stretched the fascia of that muscle. The fascia is a great constrictive factor in muscle growth. The more stretched the fascia is the more the muscle will grow and the more it will have that `popping' look. Site oils stay in there long enough for the fascia to stretch. As they dissipate, the `space' left by them is replaced with new muscle tissue growth. That is the reason why when x-rays/MRIs where performed on some of the people that have 25"+ arms, there was no oil found in there. The oil dissipated and it was replaced by real muscle.
The principle is the same as the one behind site shots with steroids, but it works at a much a larger degree, because the Site Oils take that much longer to dissipate.
As well, this is the same principle behind fascial stretching. Howver, it is much more efficient with Site Oils. Best example is to imagine a baloon. You can pull on it and stretch it as much as you want, and you will stretch it a bit. But if you fill it with a liquid, you will be able to stretch it to a much larger degree than just pulling on it from the outside. This is the best way to compare the efficiency of fascial stretching versus using Site Oils.
Pain - obviously, any site shot hurts. The pain will minimise the more you inject, until it will not hurt any more. Site Oils hurt, but not as much as site injections with, lets say, Sustanon or Testosterone Propionate. However, as I said, they will hurt less and less the more you use them.
Dangers - Site Oils are safe, if certain precautions are taken, same as when injecting anything else. You always have to aspirate. Always! You DO NOT want the oil to go in a vein. Always massage the area after the shot so scar tissue build up doesn't occur. And most importantly - USE COMMON SENSE! If you have 16" arms, don't think that you will have 23" in 5 weeks! Because if you try that, you will end up with deformed looking muscles and you will be the laughing stock of the world. On a side note, people like Greg Valentino have implants, not
seo's in their muscles. It is physiologically impossible to look like these guys do with SEOs. Hopefully that puts that myth to rest.
Site Oils are there to help you break past a plateau. If your genetics indicate that you are 242 with 5% bf, but you only have 18" arms, then Site Oils will help you bring your arms in proportion.
All that I am saying is that Site Oils are there to aid the work that you do in the gym, not replace it!