Testosterone is the key hormone necessary for men to build quality shapely muscles. Do you want to know what sports supplements will skyrocket your testosterone levels? Then read on...

So, what are the safe, legal and effective ways that we men have to boost our natural testosterone levels?

I want to take a look now at 8 popular testosterone enhancing sports supplements. You may or may not have heard about all 8, but do you know if they actually work? This article will answer that question for you.

Here are the 8 testosterone boosters we will be looking at:

1. ZMA

2. Tribulus Terrestris

3. Fenugreek

4. Activate by Designer Supplements

5. 6-OXO

6. Avena Sativa

7. Tongkat Ali

8. Yohimbe

ZMA – ZMA is a designed mineral formula comprised of zinc monomethionine aspartate, magnesium aspartate and vitamin B-6. They are combined in specific ratios to supposedly maximize the effectiveness of ZMA. A 1999 study showed increases of up to 30% in free and total testosterone during an 8 week study of NCAA football players. However, this study was conducted by one of the owners of the company that holds the patent on ZMA. Not completely unbiased.

ZMA may have helped testosterone levels because the mineral zinc and magnesium play important roles in the production of anabolic hormones, especially testosterone. The study participants were shown to have borderline deficient levels of both minerals at the beginning of the study, so raising their levels to normal could have accounted for the rise in testosterone.

I wouldn't rule out ZMA completely, most people in the U.S. are deficient in both zinc and magnesium. If you are slghtly deficient in zinc and/or magnesium ZMA could increase your testosterone production by bringing your levels back to normal. 8 out of 10 stars!

Tribulus Terrestris – This is a weed that grows in temperature and tropical climates and has been used for centuries to increase libido in males. Does it also increase testosterone levels as many supplement companies would have you believe? That depends on who is taking it.

Tribulus terrestris HAS been shown to increase testosterone levels by as much as 30%, but only in individuals who have low testosterone levels to begin with. It will raise your levels to normal, but it will not raise them if you already have normal testosterone levels.

So, tribulus terrestris is partially useful as a testosterone booster. If you are overtrained, if you are on a low calorie ‘cutting' diet or if you are recovering from steroid or prohormone use (as part of PCT) tribulus terrestris can be useful n raising your testosterone levels. Don't expect that it will give you super high test levels or significantly increased libido. 6 out of 10 stars!

Fenugreek – Fenugreek is an herb found primarily in Indian food. It has historically been used by nursing mothers to increase milk production. Studies on fenugreek are scant, but it has been shown to decrease blood sugar levels of type II diabetics.

Fenugreek has become popular recently as a testosterone booster in bodybuilding supplements. There is no proof at all that this is true. Fenugreek could be useful as a cutting aid however, due to its effect on blood sugar levels. 2 out of 10 stars!

Activate - This is a new product that says it will free up your testosterone and give you increased strength and focus. The active ingredient has been trademarked under the name Divanil and is an extract of the stinging nettle plant.

Your body has both free testosterone and bound testosterone. Only the free testosterone is of use to you in building muscle. So, you may have high testosterone levels, but if all of it is bound it is useless to you for muscle building.

Your body controls the amount of free testosterone through a protein called Sex Hormone Binding Globulin (SHBG). The SHBG binds to your free testosterone making it unavailable for muscle building. Activate works by inhibiting (decreasing) the SHBG in your body. This means more of your testosterone is free to help with your muscle building.

There are no studies confirming the rise in free testosterone levels, but there are studies showing that lignans from stinging nettle extract inhibit SHBG and user feedback is almost unanimously positive. I myself have used Activate several times and find that it increases focus in the gym, hardens my muscles and also increased libido. 10 out of 10 stars!

6-OXO – This is a product developed and trademarked by Ergopharm. The active ingredient is 4-etioallocholen-3,6, 17-trione. There have been several short term studies done that show 6-OXO increases total and free testosterone. These studies while small have shown average free testosterone increases of 126%. Additional long term studies are being conducted and initial reports point to the effectiveness of 6-OXO as a testosterone booster. 9 out of 10 stars!

Avena Sativa – Please don't believe the hype behind avena sativa. Avena sativa is the scientific name for wild oats. While I enjoy oatmeal as a good source of carbohydrates it is not a testosterone booster? No way! Even though it is being marketed as a testosterone booster there are no studies or historical evidence that avena sativa can help boost testosterone levels. 0 out of 10 stars!

Tongkat Ali – Tongkat ali is an extract from the root of the Eurycoma shrub found mainly in Malaysia and Indonesia. It is also called Longjack and Eurycoma Longfolia.

It has been used for centuries in southeast Asia to boost libido and as an aphrodesiac. Studies confirm that it works very well, increasing both sexual function and endurance as well as libido.

Researchers are unsure how Tongkat ali works, but they believe that it both increases testosterone production and increases free testosterone. Like a 1-2 punch. Common effects from Tongkat ali are increased well being, better body composition, increased libido and increased focus and aggression.

Tongkat ali does take some time to start working so it may take up to 2 weeks before you start to see its effects. You also need to make sure you are getting an extract of the root powder and not just root powder. The extract is more expensive, but necessary. 8 out of 10 stars!

Yohime - In addition to its role as a fat loss aid yohimbe has also been sold as a testosterone booster. While it does aid in fat loss through several mechanisms, there is no proof that it boosts testosterone levels.

It is likely that people believe it increases testosterone because it does increase libido, however the libido increase is not due to a testosterone increase. One of the main effects of yohimbe is that of a vasodialator expanding blood vessels, especially those in the lower extremeties.

Yohimbe has also been shown to have several negative and possibly dangerous side effects and many physicians advise their patients not to take yohimbe because of these side effects. 3 out of 10 stars!