Oxandrolone is a synthetic androstane steroid and a 17α-alkylated derivative of DHT.    It is also known as 2-oxa-17α-methyl-5α-dihydrotestosterone (2-oxa-17α-methyl-DHT) or as 2-oxa-17α-methyl-5α-androstan-17β-ol-3-one, and is DHT with a methyl group at the C17α position and the C2 carbon replaced with an oxygen atom.    Closely related AAS include the marketed AAS mestanolone (17α-methyl-DHT), oxymetholone (2-hydroxymethylene-17α-methyl-DHT), and stanozolol (a 2,3- pyrazole A ring -fused derivative of 17α-methyl-DHT) and the never-marketed/ designer AAS desoxymethyltestosterone (3-deketo-17α-methyl-δ 2 -DHT), methasterone (2α,17α-dimethyl-DHT), methyl-1-testosterone (17α-methyl-δ 1 -DHT), and methylstenbolone (2,17α-dimethyl-δ 1 -DHT).   
As for mechanisms of action, ecydsteroids seem to be able to cause a rapid Ca2+ influx in myocytes which leads to phosphorylation of Akt and thus protein synthesis.  This effect occurs after 10s of incubation, and is inhibited by PI3K inhibitors like seen in other studies, but also GPRC and PLC inhibitors; and when the cells are depleted of intra-cellular calcium Akt does not get phosphoraylized, and binding free calcium with EGTA lowered protein synthesis from 16% to 8%.  Calcium per se can be an important mediator of Akt and protein synthesis  , and ecdysteroids seem to work vicariously through Ca2+ and Akt.