Testosterone is probably the most well-known hormone and everybody who is after big muscle gains wants to know how to increase its levels. The main job of testosterone is muscle growth and it also helps to burn up fat and establish the sexual qualities of yours. Testosterone causes muscle growth by stimulating protein synthesis straightaway. men produce testosterone in the testes of theirs and ladies produce it in their adrenal glands, however in much smaller quantities then guys do. That is why it is easier for males to grow huge amounts of muscle.