Well the term of muscle hardners usually comes from drugs that are usually non-estrogenic. For example, good hardeners are halo and masteron. High androgen drugs that do not convert into estrogen thus giving your muscles a more dense appearace. Thse drugs put the body in a more favorable position to burn bodyfat. The increased blood cells you get gives you a greater pump and more overall muscle fullness. That combined with no extra water retaining effects from aromatizable drugs and you get a "muscle hardener." BTW - Drugs like test can be as well as long as you add a good amount of anti-estrogens in there.
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