Tibolone has tissue -selective estrogenic effects, with desirable effects in bone , the brain , and the vagina , and lack of undesirable action in the endometrium and breasts .  Its tissue selectivity is the result of metabolism , enzyme modulation (., of estrogen sulfatase and estrogen sulfotransferase ), and receptor modulation that vary in different target tissues, and differs mechanistically from that of selective estrogen receptor modulators (SERMs) such as tamoxifen , which produce their tissue-selectivity via means of modulation of the ER.   As such, to distinguish it from SERMs, tibolone has been described as a "selective tissue estrogenic activity regulator" (STEAR),  and also as a "selective estrogen enzyme modulator" (SEEM). 
As a result, Trenbolone Acetate now functions as the primary anabolic compound (aka the ‘workhorse’ compound) that will function to provide the muscle growth throughout the cycle. Trenbolone is strictly an advanced level anabolic steroid, unfit for use by beginners of any type. In this cycle, the Acetate variant of Trenbolone is utilized simply due to its seamless compatibility with Testosterone Propionate. This is because the Propionate and Acetate esters as, previously mentioned early on in this section of the profile, both possess almost identical half-lives (3 days for Trenbolone Acetate and days for Testosterone Propionate). This therefore provides an ease of convenience for the user, as well as smoother injection and administration frequencies. The fact that Testosterone is being utilized at a low enough doses to avoid aromatization, combined with the fact that Trenbolone’s inability to convert into Estrogen at any dose should result in the total elimination of any potential water retention, bloating, gynecomastia or any side effects associated with Estrogen . It is important to note that this cycle in particular is strong enough to be utilized as a bulking cycle, lean mass cycle, or cutting cycle – all without the inflated potential for water retention or other Estrogenic side effects .