Hard to say because of the interaction of so many dependent pathways involved in increasing muscle mass. And depending on that, it could also increase estrogen which would offset the T's effect. For example, if you take testosterone cypionate injections (assume normal T levels, but suboptimal free T) you will see increases in muscle mass, libido, erectile function. But if you take clomiphene which increases LH/FSH and stimulates your body's endogenous production of T, you will get optimal T, and free T. But also, skyrockets estrogen, lowers libido and erectile function, with minimal increase in muscle mass.
