increased testosterone from working out is probably around 10-30% long time, which is a far lower variance than natural level variance in healthy adults. i think i heard from several (claimed natural) strength and bodybuilding athletes that their total testosterone is at the lower end of the scale.

that said, natural free test levels are at a fraction of what enhanced pro bodybuilders tend to supplement, and there are mass monsters with hair. cutler, yates, ferrigno and golden era bodybuilders like schwarzenegger, zane, columbu all had full heads of hair.