1046 ng/dL Increase in Testosterone for 1.5kg Lean Body Mass in 16 Weeks

Before you read on: This was a study done on 112 men aged 65–90 years, so the results are only partly significant in view of the effects of testosterone supplementation on younger men.

In a double-masked 2x3 factorial design the scientists administered testosterone gel (5g/day vs. 10g/day via Leydig cell clamp) and rhGH (0 vs. 3 vs. 5 µg/kg/d) to the subjects who had a mean baseline testosterone level of 493ng/dL. They summarize the results for the testosterone and the testosterone + rhGH groups as follows:

Increases in total testosterone of 1046 ng/dL (95% confidence interval = 1040–1051) and 898 ng/dL (95% confidence interval = 892–904) were necessary to achieve median increases in lean body mass of 1.5 kg and appendicular skeletal muscle mass of 0.8 kg, respectively, which were required to significantly enhance one-repetition maximum strength (≥30%). Co-treatment with rhGH lowered the testosterone levels (quantified using liquid chromatography–tandem mass spectrometry) necessary to reach these lean mass thresholds. 

So, in view of supplement producers boasting with "all natural" products boosting natural testosterone levels by up to 80% , the fact that a 112% boost in testosterone delivered a mediocre increase of 1.5kg in lean mass over 16 weeks should remind you that even with the most effective natural test booster, a sound nutritional regimen and an intense workout plan are a must to see those results in muscle tone and size you are probably striving for.