Facial mucles

You sometimes see some great jazz trumpet players frowning like their face is about to explode while playing. And yet they manage to get some dynamite music out of their horn! 

It might work for some people but I would advise you not to emulate them. Facial tension will spread through your body and eventually affect your air flow and your tone. While some truly great artists with strong personalities and creativity will succeed this way and even make it their trade mark sometimes, it won't work for the vast majority of people who will end up with a mediocre tone and less endurance as a result of too much frowning. 

You need to know which muscles are actually needed to play your horn and leave the rest as relax as possible. Forcing with your forehead might give you some short term results but will hurt you in the long run. Have the patience to learn to play in a relaxed manner and you'll eventually gain strength and endurance to play without unnecessary facial tension.