A commonly used protocol for determining the androgenic:anabolic ratio, dating back to the 1950s, uses the relative weights of ventral prostate (VP) and levator ani muscle (LA) of male rats. The VP weight is an indicator of the androgenic effect, while the LA weight is an indicator of the anabolic effect. Two or more batches of rats are castrated and given no treatment and respectively some AAS of interest. The LA/VP ratio for an AAS is calculated as the ratio of LA/VP weight gains produced by the treatment with that compound using castrated but untreated rats as baseline: (LAc,t–LAc)/(VPc,t–VPc). The LA/VP weight gain ratio from rat experiments is not unitary for testosterone (typically –), but it's normalized for presentation purposes, and used as basis of comparison for other AAS, which have their androgenic:anabolic ratios scaled accordingly (as shown in the table above). In the early 2000s this procedure was standardized and generalized throughout OECD in what is now known as the Hershberger assay.
As a bulking agent, the effects of Masteron will prove to be rather weak. It is possible the hormone could provide gains in mass similar to Primobolan (which wouldn't be that strong either) if the total dose was sufficiently high. However, the relative gain in size will be moderate with many anabolic steroids being far more suited for this period of steroidal supplementation. Masteron does not aromatize and is not estrogenic; in fact, it shows anti-estrogenic traits in the body and binds to aromatase instead of other substrates. This is why it has been effective in the treatment of breast cancer.