| The musicians in the symphony, opera and chamber orchestra play sitting down.
You also can practice sitting down. Straighten your head and spinal column and sit on the first third of the chair (see picture left) so that the diaphragm could function normally, ie. allow you proper breathing.
It is not good to lean back in a chair when practicing (see picture right), because such a position is bad for concentration, disrupts the proper playing and harms your health.
Soloists on various instruments and members of military bands play in the standing position. I recommend this position, because it will enable you to carry out the described technique of breathing easily. Therefore p (piano) and f (forte), are better performed and it makes the intonation of the high tones easier, more correct and accurate.
When standing, straighten the body, then make a little and soft gap between feet. You need to have the feeling that all the body weight falls on the feet, not on the heel. Toe of one foot will serve you for a barely noticeable ticking. Ticking should be easy, relaxed (not in spasm!) and not done by rocking the entire body and the clarinet tone. Everything related to the position has been stated in the chapter on Holding the Clarinet.
Use the sitting position only when you are tired.
Taken from my book