They have the size to do it, that's number one. The are taking enough gear not to become a shrivel up flat bread with no muscles. No way they will lose muscle or flatten up with the amount of insulin they put in them.
And it depends on every individual, forsure they all need t3 as they are using so many things that will reduce the natural production of the thyroid. But for fat loss, I am sure they mostly depend on their 30+ ius of blue top fda saizen. The t3 will definitely assist, but that gh is the priority, it helps to keep them lean on off season, and once it's time for prep, they can start cutting 8 weeks out. They look fatter than they appear from excessive water retention. But once prep starts, up the diuretics, up the tren, start reducing testosterona, blast the anadrola like they dont got no liver to give a rats ass about, and start manipulating the gh doses as this is the most critical drug in their prep, insulin comes next to bring that freakish full heavy weight look on stage. Most of them eat like crap and still stay lean on off season. Gh is the key to success lol, the last thing they would worry about is running too much t3, I doubt 100-250 will affect them with the abuse of oral and injectable steroids, growth hormone, and insulin. If they can, they will do it. Speeds up the cutting. That's bodybuilding, if it helps, it will be in them at a crazy dose.