Forget what all these f**k wit, know it alls say about low SHBG levels will mean you have greater amounts of free Testosterone and thus will have greater gains in muscle mass.

They are talking bollocks.

SHBG is basically the transport system for your hormones. Without SHBG no matter how much testosterone you inject you will not see much if any muscle gains. Why?

Well without SHBG you would almost totally be relying on the localised action of Testosterone. SHBG is what transports your testosterone to the cells that need it most, in the case of heavy weight training your muscle cells.

Low SHBG levels have been linked to male obesity and Type-2 diabetes.

So what causes your body to lower SHBG levels?

High concentrations of Androgens can lower SHBG levels.

What increases SHBG levels?

Estrogen and the Thyroid hormone T3 are two things that will help your body increase SHBG.

So all these guy's who tell you to use Proviron etc to block aromatisation could be setting you up to become a Type-2 diabetic.

One way around it is to either use T3 in all your cycles or do lots of aerobics which can help strengthen your natural thyroid.

Studies that have assessed adipose tissue distribution by imaging techniques such as computed tomography have demonstrated the importance of the intra-abdominal (visceral) fat depot as a marker of a cluster of metabolic abnormalities which include glucose intolerance, insulin resistance, hyperinsulinemia, hypertriglyceridemia, elevated number of apo B-carrying lipoproteins as well as hypoalphalipoproteinemia. Although the association between visceral obesity and metabolic complications can hardly be questioned, it has been suggested that it may not necessarily represent a causal relationship. For instance, concomitant alterations in sex steroid levels have been found in both men and women with abdominal (visceral) obesity which have also been reported to be significantly correlated with the insulin resistant-dyslipidemic state found in abdominal obese subjects. In women, abdominal obesity is associated with increased free testosterone concentrations and reduced sex hormone binding globulin (SHBG) levels whereas this condition is associated with reduced testosterone and adrenal C(19) steroid (DHEA, androstenedione, androstene-3�,17�-diol) levels as well as decreased SHBG concentrations in men. These altered steroid and SHBG levels have been reported to be independent correlates of the metabolic complications of visceral obesity.

Taken from "The Journal of Endocrinology".

Put that in you pipe and smoke it.

Here we go again, you don't think SHBG is responsible for the Transport of Testosterone around the body.
http://www.scrippslabs.com/graphics/pdfs/SHBG.pdf

Read especially the bit "SHBG enhances the EXCHANGE of these steroids in central tissue".

You said yourself "high concentrations of androgens lower SHBG levels." You totally contradicted yourself when you said "without SHBG, there would only be localized growth." With that statement, basicly what you're saying is that if you inject exogenous test, it will lower SGHB levels. That would mean that you would only get localized growth.
If SHBG was the only way to transport testosterone, then it should increase when introduced to high concentrations of androgens. However, it does not therefore there must be another method of actual transportation.

Well quite a high percentage of both Test and Estrogen is transported by SHBG.

As for the localised growth thing, SHBG will not decrease from just injecting extra TEST, as long as there is a concurrent increase in estrogen.

This is what I have been trying to get through to people for a long time. The combined increase in estrogen associated with taking Testosterone is important in so many ways.

Estrogen increases SHBG which in turn prevents type-2 adult onset diabetes. Estrogen also increases energy and mental alertness.