Boosting anabolic hormone (testosteron) with Tribulus Terrestris

Although each of the anabolic hormones (testosterone, growth hormone, insulin, lGF-l) is required to stimulate maximum levels of skeletal muscle hypertrophy, testosterone may be the most anabolic. It is important to recognize that not all of the testosterone in the blood is bioavailable; rather, most of it is bound to proteins such as sex hormone binding globulin (SHBG) or other carrier proteins. Testosterone that is not bound is referred to as “free” or “bioavailable” testosterone; and it is able to bind to the androgen receptor and exert its anabolic signaling.

This is an important distinction because as one attempts to increase testosterone levels
(via testosterone-enhancing supplements) in the body, it is only the bioavailable testosterone that exerts anabolic actions. Another important consideration is the avoidance of increasing SHBG to a greater extent than total testosterone increases, which would result in an environment in which there is less bioavailable testosterone present. Therefore, when investigating sports supplements designed to increase testosterone, each of these factors must be considered.

Currently, there are a few sports supplements that claim to increase testosterone levels: ZMA, Tribulus terrestris, and aromatase inhibitors.

Tribulus terrestris
Tribulus terrestris is often marketed as a testosterone-boosting sports supplement. There are relatively few, if any, scientific studies to substantiate these claims. In fact, one clinical investigation demonstrated that Tribulus terraslris exerts no effect on increasing testosterone levels (94). In this study, healthy men were instructed to supplement with T ribulus terrestris for a 4-week period after which serum levels of testosterone and luteinizing hormone were measured at l, 3, IO, 17, and 24 days after supplementation. Tribulus terrestris supplementation did not increase the levels of either testosterone or luteinizing hormone. Given the unsubstantiated claims of Tribulus terresrris relative to increasing testosterone levels, supplemental Tribulus is not recommended.

Reference

Nutritional Supplements in Sports and Exercise - Douglas Kalman, Mike Greenwood, Jose Antonio