http://cdn.intechopen.com/pdfs/410...teroids_application_in_sport_and_exercise.pdf
https://academic.oup.com/jcem/article/95/4/1533/2596379
So the earliest account in the US would be the late 1940s. Let’s go back and say 1945, which is even a bit earlier than the late 40s, and it’s unlikely that American bodybuilders were importing testosterone from Europe, especially from Germany or even Russia, during World War II. So the picture from 1947 MAY not be natural if you prescribe to the earliest timeline, but the ones from 1941 are almost certainly natural.
In 1929 Butenandt isolated 15mg of androsterone from an 15-25 THOUSAND LITERS of police man urine. So that’s not feasible to use at all.
Ruzicka then synthesized it in 1934, but it still wasn’t feasible to use.
“In 1935 Ka`roly Gyula David, E. Dingemanse, J. Freud and Ernst Laqueur, backed by the Organon Company in Oss, The Netherlands...” identified testosterone in the testes, so it wasn’t usable then either.
Later that year it was first synthesized from cholesterol, but that likely wasn’t even close to being feasible for bodybuilding cycles either.
https://www.jurology.com/doi/pdf/10.1097/00005392-200102000-00004
The first clinical trials began in 1937, so we KNOW that it wasn’t being used before then.
http://www.mvla.net/view/20926.pdf
It’s also unlikely it was available in quantities sufficient for bodybuilding use, and also unlikely that random bodybuilders would have had access to what was at the time a newly discovered hormone just starting to be used in clinical trials.
Source: “The History of Testosterone and the Evolution of its Therapeutic Potential”
It’s still rather unlikely that bodybuilders had access to it at sufficient doses to cycle effectively at this point (1940).
The following is the EARLIEST date I’ve been able to find:
Source: “The Long and Tortuous History of the Discovery of Testosterone and Its Clinical Application”
So, assuming that some bodybuilders were WAY ahead of the medical understanding of testosterone and got doctors to prescribe it to them in higher doses to build muscle, it’s possible that they started, at the earliest, at the VERY END of the 1930s, or the beginning of the 1940s. It was likely used by at least some bodybuilders in the mid-late 40s, even more likely and prevalently in the early 50s, and definitely by the mid 50s.