One of the fairly common problems that I have found on the Peak Testosterone Forum is low SHBG. Low SHBG should be a good thing, because it will boost one's free testosterone. Unfortunately, it doesn't work that way and low SHBG is actually a powerful sign (usually) of fatty liver and insulin resistance, something I discuss in more detail on this page: Root Causes of Low SHBG. And once insulin resistance sets in, many problems, such as fatigue and erectile issues, often accompany it. Plus, a significant block of men with low SHBG are also low testosterone (and low estradiol) and, therefore, have double trouble. They also find that, if they go on TRT, they have tremendous difficulty getting "dialed in." The bottom line is that almost every low SHBG man is really struggling to feel good.
I do have good news though: there are natural strategies that can help to significantly boost SHBG and one of them is exercise. The subject has actually been examined in a number of studies for the purposes of prostate cancer prevention with the idea that exercise my increase SHBG, bind to testosterone and thus be prostate protective. (The concept that testosterone causes prostate cancer has since becomecontroversial however with some experts saying that it is actually low testosterone that increase prostate cancer risk.)
Below is a summary of what the researchers have found to date:
1. Sedentary, Healthy Men. One study examined sedentary senior men with no major health issues and had them exercise on stationary bikes. Blood samples were taken every 10 minutes and what they found was that both testosterone and SHBG spiked during exercise and then quickly returned to baseline.  The reason for this is a phenomenon called hemoconcentration, which simply means that the volume of blood changes during exercise. This can be a good thing during the short time that it happens, but it does really mean that the body's total amount of SHBG (or testosterone) has really increased.
2. Athletes. A study published in the same year found similar results in athletes, i.e. that both testosterone and SHBG spiked after exercise but quickly returned to baseline.  Coupled with the study in #1, this would indicate that likely all men can give themselves a nice short term boost in key hormones and proteins, which may partially explain why most men feel so good when they exercise - that is, after they get over the initial pain!
3. What About Long Term? Of course, the all-important question is if exercise can boost SHBG on a more permanent basis. Fortunately, we have a study that looked at this and the answer appears to be 'yes.' Researchers examined a 100 sedentary men between the ages of 40 and 75 and found that their SHBG had increased 5.7% at the 3-month point and 8.9% at 12 months.  Notice that the trend is upwards and so it is possible that SHBG would continue to rise even a little more if exercise was continued longer than 12 months.
CONCLUSION: Some of you low SHBG guys may be thinking, "Okay, that's nice, but I need a lot more than a 9% boost in SHBG!" My response to that is that pulling up low SHBG requires a multi-pronged approach, where exercise is just one of the lifestyle changes that need to occur. And the reason is simply this: insulin resistance is, of course, partially a function of lack of exercise. However, it also has a dietary component as well. The root cause is that liver cells get stuffed with fatty acids - literally "bloated" and unable to function properly. To clear that out requires a total lifestyle change.
One of the men on our form - his alias is Sam - did just that and outlined his approach here: How to Cure Low SHBG. As a followup, he doubled his SHBG and is now doing much, much better. His fatigue is largely gone, and his "program" has improved his work performance, etc.
1) Metabolism, 1996 Aug, 45(8):935-9, "Exercise increases serum testosterone and sex hormone-binding globulin levels in older men"
2) Eur J Appl Physiol Occup Physiol, 1996, 72(5-6):425-9, "Differential effects of exercise on sex hormone-binding globulin and non-sex hormone-binding globulin-bound"
3) Med Sci Sports Exerc, 2008 Feb; 40(2): 223 233, "Effect of Exercise on Serum Sex Hormones in Men: A 12-Month Randomized Clinical Trial"