I am really working hard to chill-out on the band stand, which is no easy task. As a perfectionist (many musicians are) my body tends to tense-up as I play, but very few of those muscles are needed to play the music. In fact, they get in the way of an efficient and musical performance. It is hard to move fingers and arms quickly when they are in a permanent state of "flex" or agitation. The same goes for your oral cavity for wind players. With tension comes the restriction of air flow and a cumbersome tongue. So, relax, "hear" what you want to play, and have some fun.