You got a link to the study?
In men, 70% of circulating testosterone binds with high affinity to plasma sex hormone binding globulin (SHBG), which determines its bioavailability in their target cells. In recent years, a growing body of evidence has shown that circulating SHBG not ...
www.ncbi.nlm.nih.gov
Again, still only hypotheses but interesting nonetheless.
Paraphrasing, megalin on the surface of cell membranes facilitates the transport of shbg
bound sex hormones across cell membranes. Once inside the cells, the lower pH of the intracellular environment causes dissociation of the sex hormone from SHBG (changes in pH denature proteins), and the hormone is now free to bind to the AR. Pretty straightforward but hasn't been proven yet per se. There does seem to be data showing that Megalin does exist on muscle cell membranes and lending credence to the idea.
Another hypothesis is that an as yet unidentified receptor exists on cell membranes that allows SHBG with bound test to antagonize the AR. This states that molecules of shbg (having multiple binding sites) will bind to a sex hormone, and another shbg binding site binds to the receptor on cell membranes. (I need more reading on this part) Then the test+SHBG activates an intracellular protein that causes the accumulation of intracellular cAMP, which subsequently activates protein kinase, and protein kinase
may antagonize the AR.
Again, both are only hypotheses I need to read more on the second one...when I have time lol. Life is not allowing me much leisure reading time. But both would still seem to point to testosterone molecules being necessary for AR activation, but would not preclude some initiation of AR activation from the currently bound testosterone.
Overall, I still think the focus on SHBG is mostly pointless. Especially if one is using There are much bigger concerns trying t recover from strenuous exercise.
As in, low shbg is not the cause of poor recovery, merely a symptom of the body being overworked and responding in a manner to preserve sex hormones. The concept of shbg serving as a timing/storage mechanism during these periods seems plausible.