muscle fiber diameter, the number of myonuclei present in muscle fibers,
 the absolute number of satellite cells and the percentage

of satellite cells relative to myofiber. Most bodybuilders realize that estrogen must be reduced

 during cycles, but completely blocking the actions of estrogen may not be a good thing. 
 Combined estrogen/androgen implants are more 
effective than either androgens or estrogens alone in stimulating muscle growth. 
 In the journal of Domestic Animal Endocrinology researchers reported that both estrogens and

 androgens enhance satellite cell activity in bulls.  Treatment of satellite cell cultures 
with either estrogen or testosterone resulted in a 
concentration-dependent, threefold, increase in IGFI mRNA expression.  I consulted 

Dave Palumbo on this study and he agrees that complete suppression of estrogen can hinder 
muscle mass gains; the key to muscle growth
 is to minimize estrogen not completely eliminate estrogen.

Kamanga-Sollo E, White ME, Hathaway MR, Chung KY, Johnson BJ, Dayton WR.

 Roles of IGF-I and the estrogen, androgen and IGF-I receptors in

estradiol-17beta- and trenbolone acetate-stimulated proliferation of cultured bovine

 satellite cells. Domest Anim Endocrinol. 2008