Besides taking supplements there is another way to increase testosterone levels. The author of this article participated in a study where he was asked to take up different power positions that symbolized authority - putting the feet on desks, doing a hawk pose and all those. Within 15 minutes his testosterone levels doubled.
There's almost no practical way I can incorporate this into my practice (huh? you're asking me to put my feet on the desk?) but it does not mean there's no value in it. What I think is more important here is mind/body over matters. If you exude confidence then it shows in your posture and actions leading to a physiological advantage. This is also a reminder that a lot of life's battles are won or lost in our minds even before we enter the battlefield. And even if you have not always felt particularly confident, thank goodness for a way to short circuit your body into believing that you are - just clear those desks!