I would want to read the original references before concluding that total delivery in fact was greater.
It is very easy to have error in measuing AUC, and differing error when the curves are different, as would be the case here.
E.g., suppose your protocol is that you do blood draws at 15 min, 30 min, 1 hour, 2 hours, and 3 hours. (Just making up figures.) It may well be that for one method of administration, one of these measurements is right at the peak or virtually so, and none of them are at a lag time; while for the other method the peak falls right between two measurements, which are both far less than peak. In this case, even if true AUC is identical, the first measured value will be higher or even much higher.
The reason I suspect error is that it is not as if any of the GH injected sub-Q is going to be removed from the body via transporter beam, nor do I think it will be broken down at the site. It has nowhere to go but the bloodstream. Either sub-Q or IM should approach 100% bioavailability, thus there can be little room for actual improvement in this regard between one or the other.
That said, myself I like IM better.
The article had very interesting points with regard to different patterns of male vs female GH release and response, and the information on steadier lower levels, for same total amount, being much less desirable than rapid high peaks. And the information that IM gives higher peaks, combined with that, is a good reason for preferring the IM, at least as a better bet, even if the relative bioavailability measurements suffer from systematic error as I suspect is highly likely. (A lot of published scientific articles have errors in them, by the way. It’s not unusual at all, unfortunately.)
But as a caveat before considering it proven better, the article also states:
“While GH delivery was vastly improved with intramuscular injections, IGF-1 concentrations were no different between subcutaneous versus intramuscular injections following the same (single) dose. Thus, it is unclear at this time whether intramuscular administration would provide any anabolic or tissue repair benefits. Hopefully, further research will clarify this point with long-term studies.”
(The IGF-1 concentrations being no different is another reason to suspect error in the measurements of AUC being different between IM and sub-Q. If there were a real difference, then why same IGF-1?)
Final note: I had a previous version of this post that was fucked up. If you read that, and now see this, that’s why this replaces that.