Having recently competed at the Grand Shield, where "Red Priest" requires the entire cornet section and the trombones to stand throughout the performance, and with Whit Friday less than a week away, I have become more conscious of the important differences between standing and sitting during playing. The effect of the differences in standing and sitting to posture, breathing and therefore playing in general can be quite dramatic.
The upright, standing position is naturally the best. A position we should try to emulate when sitting. We should never slouch. The back should be straight and free from tension. An easy way to ensure good posture when standing is to think of a string pulling the top of the head upwards, almost causing you to stand on your tip toes, the neck stretching up off the shoulders. In a sitting position, the only difference should be in the legs - which should bend to allow you to sit over your bones (i.e. the spine).
I often see people playing with poor posture, whether standing or sitting. They would sound so much better if they followed the simple trick above. When I'm teaching, I always demonstrate and work on players' posture. I believe a good posture ensures good breathing, which ensures good sound - the key to all good playing.
As with anything in brass playing, like embouchure for example, there is a universally recognised "right way", but there are as many exceptions to the rule as there are examples. Some players can slouch over, almost as twisted as a contortionist, and be one of the best players in the world. However, if you stand/sit with good posture, as outlined above, and your playing improves - why wouldn't you maintain this posture?
