It seems like TT should be the X variable and FT should be the Y variable, no?
You’re TT would depend on how the ester releases the testosterone, right? How could your FT levels influence how quickly the ester releases the testosterone?
Also, your answer seems to imply that higher SHBG men don’t need higher doses of testosterone. Do you believe that?
The injected ester is cleaved to release free T, not Total T. Your body then takes that fT and it gets metabolized into downstream products as well some of it reacts with SHBG (as well as albumin) to form bound and weakly bound T. TT = fT + SHBG-bound T + albumin-bound T. SHBG-bound T is a reservoir for fT. Here's some reading...
Blatant reproduction of
@Cataceous 's post (with full attribution though

):
Adding this (I’ve put on here in a few places) here as this is the most succint description of the confounding of SHBG vs injection frequency requirement I’ve found (attribution to cataceous on
ExcelMale): The issue with this study is that they are basing MCR on total T rather than free T...
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TLDR: doesn’t matter. More details that are of probably little help but may interest some. Thought about your question which was reason for delay in responding and trying to answer as succinctly as possible based on the constructive feedback I’ve received recently. I FAILED! If your goal...
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ripped the text out of this post:
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TLDR: doesn’t matter.
More details that are of probably little help but may interest some.
Thought about your question which was reason for delay in responding and trying to answer as succinctly as possible based on the constructive feedback I’ve received recently. I FAILED! If your goal with respect to question is to maximize muscle growth then my short answer is I don’t think it matters. Area under the curve (how much your body processes) will be proportional to dose so whether you do cyp or prop doesn’t matter.
Guys who have low SHBG need to inject more frequently?
SHBG is related (correlated) to but doesn’t appear to drive (causation) clearance rate. There’s a whole bunch of stuff that determines how your body clears fT, SHBG is not one of them. Your body eliminates based on free T not Total T. TT is set by your SHBG and free T via dynamic equilibrium (chemical kinetics). Guys typically look at their TT and get confused as hell when trying to understand clearance rate. This is where this idea that guys who have lower SHBG need to inject more frequently came from. For the same fT a low SHBG guy will read a lower TT so he thinks he isn’t getting the same bang for his buck even though his fT is the same as the higher SHBG guy. In addition, I’ll argue that WE don’t understand the value of keeping supra T (TT and fT) levels constant with respect to positive vs negative side effects.
Hence, for 250 mg/week of TC (mild cycle for many based on their metabolic clearance rate of free T), do we need to inject ED or once weekly if our SHBG is 10?
Remember, elimination is driven by free T not Total T. If you really want to know your elimination kinetics it will take some work as I’ve discussed a few times how you can measure AUC and determine how your body processes T. Still seems trial and error to me and related to age, liver activity, lymphatic activity, where you inject, blah blah.
Example:
So what’s the goal? Gainz or something else?
Given SHBG of 10.
Given 250 mg/week of TC.
Better to inject every day and keep constant TT (constant free T) at say 1500 ng/dL (55 ng/dL) or inject once weekly and have peak TT (fT) at 2000 ng/dL (77 ng/dL) and trough TT (fT) at 1000 ng/dL (36 nd/dL)?
Good question that I can’t answer for an individual. Running your body at constant and HIGH TT(fT) levels continuously seems like a bad idea from health perspective. From GAINZ perspective, I have no clue.
What drives GAINZ, fT or TT and what’s their individual contributions? No one knows as far as I can tell. Others thoughts or feedback?
Homework: do this same example for a guy with an SHBG of 30 nmol/L and
compute the TT / fT levels for ED vs weekly injections? What does this tell you?
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May be of interest. See plot linked therein. Big difference between endogenous T production with an intact HPTGA vs using exogenous T where one uncouples negative feedback loop between T/E2 and hypothalamus/pituitary. With endogenous T production there is typically strong correlation between...
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See first two pages of review article above. Bioavailable (“free” + “weakly bound”) T assay is a very standard result that attempts to measure non-SHBG bound testosterone by precipitating SHBG bound fraction using ammonium sulfate method...
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So although the calculators and math treatment of TT and fT are usually using TT as independent variable ("x-variable") and fT as the dependent variable ("y-variable"), physiologically its the opposite. I surmise because TT numbers very easy to measure historically after introduction of RIA method in late 60s / early 70s (so there's plenty of data out there). We are still waiting for accurate fT numbers (??).
I feel fortunate
@madman will let us know as soon as active researchers in the field solve the free hormone hypothesis challenge and figure out how to measure fT accurately and reproducibly between labs (harmonization program that's ongoing). I'm pulling for you
@madman.