My opinion on single-product T boosters: they need to be stacked with something. Usually an AI unless the product in question is an AI itself. Of those you mentioned, DAA and Tribulus are two such products. For men with chronically low T, these products might work well alone, but for those with normal T, the excess testosterone they produce will just convert to estrogen, which is why an AI is very beneficial.
Bulbine is different. I am not entirely familiar with the mechanism, but is my understanding that it is both an AI, and boosts test production, making it an ideal standalone compound. But beware, many bulbine products use a low quality extract which is ineffective. Prolensis is the trade name of the best extract available.
Here is a study indicating an increase in muscle nerve activity and bloodflow (excellent indicators of increased strength) following L-dopa dosage: Invalid Link Removed
I apologize that I could not find a study involving a measured force increase in muscle strength, but those indicators should at least tell you that a strength increase would be likely
Here is a study which found a significant increase in endurance of cyclists following l-dopa dosage: Invalid Link Removed
Here are two related studies on dioscin (the active ingredient in Tribulus and Fenugreek products) and GH release: Invalid Link Removed
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There's a ton of anecdotal evidence from dopamine-deficient people indicating that tribulus and fenugreek work to increase dopamine levels. I couldn't find a study I liked which confirmed their ability to inhibit dopamine b-hydroxlase, but I think I may be able to locate one if I have more time. Theres not a ton of research yet because this is a relatively new discovery, and it's an herb so pharma does not stand to make a profit off it. But the proposed mechanism is that it inhibits the enzyme which breaks down dopamine, so it would make sense that dopamine levels are increased therefore stimulating muscle nerve activity and bloodflow, inducing strength increase, as well as stimulating the HPTA.
The reason why tribulus gets a bad rap is because a ton of trib products are crap. They contain only trace amounts of the dioscins you would want. A product with at least 20% protodioscin is my reccommendation.
For a synergistic effect, take L dopa along with a high quality fenugreek or tribulus product. This would work in a manner similar to how an aromatizing anabolic steroid must be taken with an AI to block estrogen conversion. But be careful. I once did this for too long and woke up one day feeling HIGH. I was FLYING. And my libido was driving me insane. Didn't take long for me to realize that I had screwed up my dopamine levels, but stopping supplementation and starting on Ashwagandha helped clear up the issues I was having pretty quickly.
So to sum it up, at least two types of testosterone-boosting compounds act on dopamine levels in the body. The dopamine itself seems likely to be the source of increased strength. Increased testosterone is probably only slightly responsible for the increased strength but MAYBE it works highly synergistically with the increased dopamine. Hard to tell. Brain chemistry as it relates to the HPTA is a complex puzzle.
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