There aren't any proteins attached to free testosterone and is unbound to any other molecules. It can enter cells and activate receptors to effect your body and mind. Despite free testosterone's benefits, it only takes up 2-3% of our total testosterone.
SHBG takes up about 40% of the bodies total testosterone. It is produced in the liver and regulates the amount of testosterone in the body. Our body can't use this type of testosterone to boost muscle or influence or mood. Research suggests that it can regulate the amount of SHBG so that it doesn't attach itself to the Free Testosterone (that's the pure kind).
This is a protein produced in the liver and it's job is to sustain fluid levels. Orbium Bound Testosterone can easily be turned into Free Testosterone. If you are checking your testosterone levels, make sure they give you the breakdown for this one.
Signs of low testosterone include lack of sex drive, no libido, depression, mood swings, lack of sleep, balding, bloating, lack of energy, increase in body fat, and decrease in bone mass. Your testosterone production can decrease by not eating enough or feeding your body with appetite suppressing drinks. Another proponent of testosterone is sunlight. In our culture, we spend many hours of the day at home behind a computer, when our body needs Vitamin D3, which is produced through exposure to sunlight.
You should be able to call your doctor to have your testosterone levels tested. If you do get yourself tested, and you do find out that you have low testosterone, there are ways to fix it before resorting to hormone replacement therapy. You should commit 4-6 months changing your lifestyle and this will increase your hormones. Studies have shown you can increase your natural testosterone levels by 300% by maintaining a sleep pattern. If you do stay inside quite a bit, you can take Vitamin D3 and Omega 3.