muscle

Tremolo is created at the vocal folds, opening and closing in a rhythmic fashion. This controlled muscle is also often used for articulation. In fact, it's the primary articulation (think slight cough) used for blow notes in post war Chicago blues (except for chugging, where the "T" and "K" articulations are more common). Though not common for draw notes, you can use it as well, especial for fast passages when tongue blocking (a lick in Little Walter's "Evan's Shuffle" comes to mind where I consciously used it, the 5 draw at 1:04).

Continuing on the theme of the importance of being relaxed while playing for good tone... relax your neck/throat muscles. While performing the tremolo for example, only the muscles that are involved in the opening and closing of your vocal folds are needed. While performing a bend, the tongue is the only muscle that needs to move. Engaging the neck muscles around your throat will narrow your air passage, diminishing the size of that resonant chamber, sacrificing tone production in that part of your mouth. Early fatigue is of course an issue as well when using more muscle than you need... continue reading...