The singer should achieve a ‘lateral’ expansion around your epigastric region – the area between the navel and the sternum. This also includes the lower ribs at the sides and, to some extent, the back. The sternum should be raised during inhalation, and there should be no chest displacement (collapse) thereafter. The expansion should not be forced forward in the abdomen only, as this will create tensions and limit the work of the intercostal muscles, which are mostly responsible for raising and expanding the lower ribs at inhalation in order to create more width within the thoracic cavity, (which in turn decreases the subglottic pressure).
This expansion of the lower ribs, and the use of the intercostal muscles during all breathing tasks will help the singer learn appoggio technique, which seeks to maintain that initial inspiratory position, with the diaphragm lowered for as long as is possible and comfortable, the sternum raised and the lower ribs raised and expanded for most of the sustained note or sung phrase in order to reduce the subglottic pressure. (With the chest cavity expanded and the diaphragm in its lower position, there is more ‘space’ for the air molecules because the dimensions of the thoracic cavity have been increased both horizontally and vertically, and there is therefore less subglottic pressure.) This is applicable not only to singing, but to speaking, as well.
To raise the sternum (until it becomes easy and automatic), the singer can inhale as he raises his arms over his head, then slowly lower the arms as he exhales, being sure to keep the sternum in the same position. The Garcia position – laying flattened palms (facing outwards) on top of each other and resting them on the sacrum, or lower back – is also useful for opening up the posture. This will raise the sternum, open up the ribs and keep the shoulders from rolling too far forward. The Garcia position is particularly helpful for students of voice who have poor general posture due to imbalance in the muscular strength between the back and abdomen, and who experience difficulty maintaining a raised sternum while vocalizing.
It often helps to place the fingers on the upper abdomen pointing toward the navel and the thumbs on the lower side ribs pointing toward the back, and also to breathe while standing in front of a mirror to ensure that the chest is remaining stable throughout the entire breath cycle. The lateral expansion doesn’t have to be huge or exaggerated, especially when only a small amount of air is required for the upcoming vocal task.
Lying on the floor on one’s back, with the knees bent and allowing the lower back to gently push into the floor while inhaling may also cue the singer to the feeling of proper ‘support’ from the lower back muscles. Some teachers refer to this technique or sensation as ‘breathing into the back’.
source: http://www.singwise.com/cgi-bin/main.pl?section=quickRef&doc=Breathing_InAPinch