There is a big relationship between testosterone and muscle. In bodybuilding, the old Olympics, and the professional sports world, when we talk about "doping," we mean "testosterone." Testosterone is one of the hormones naturally secreted in the human body and plays an important role in maintaining a healthy body. However, testosterone peaks in its twenties and goes downhill. Experimental results have shown that as testosterone declines with age, muscle mass and strength also decline, leading to the development of obesity, diabetes and cardiovascular disease. Even if a middle-aged man goes to the gym and trains hard, the major factor that makes it difficult to reproduce the body in his twenties is the possibility of a decrease in testosterone. Recently, it is said that there are many people in their thirties who have decreased testosterone due to the effects of stress. It cannot be judged by age. Blood testosterone levels in healthy men are said to be normal at 350 to 1000 ng / dL. If your testosterone drops sharply, you will not be able to build muscle even if you exercise. Testosterone emits various signals that thicken the muscles. However, if you are deficient in testosterone, no matter how much training or exercise you do, you will not be able to expect any effect. If you're worried that your muscles have fallen or are hard to build, it may be a wise choice to first suspect a decrease in testosterone and try something.