A comparison of the level of abdominal muscle activity and movement of the chest and abdominal wall during the performance an orchestral excerpt (from the prelude to Act 1 of Carmen) in different postures by a professional player. This is low in the trumpet range and overall, levels of muscle activity are quite modest. They are greatest when standing and lowest when sitting on a flat seat. Sitting on a sloping seat generates a level of muscle activity that is close to that of standing. The pattern of thoracic abdominal movement is similar in all positions and shows no evidence of consistent differences in degree.