An optimal singing voice requires proper posture and breathing. The posture for singing that employs the idea of standing too tall and locking the hip sockets and hyper extending the rib cage will prevent you from getting a low free breath. Maintaining the hip sockets in a locked position and/or the rib cage in a hyper-extended state will prevent access to the lower abdominal muscles essential to proper lower body support.

The correct posture for singing starts from the bottom up:

1. Feet apart or one foot in out in front of you but space between the feet. Keep the weight of your body evenly distributed on both feet but NOT on the heels of your feet. There should be a slight leaning forward sensation.
2. Knees should have the feeling of a slight bend and should remain loose while breathing and during phonation.
3. The hip sockets should remain loose in the breathing and phonation processes. You can achieve this by bending a slightly forward at the hips.
4. During inhalation keep the abdominal muscles flat, don’t squeeze them or hold them too tightly to keep them flat, but don’t allow the stomach and lower abdominal muscles to distend too much. As you ALLOW the air into the lungs imagine the air coming straight up the spinal column. You should feel the breath is filling up the back. Work to expand from the bottom up and as you fill with air allow the rib cage to lengthen, north and south. You should feel tall but not tight.

You need only a small amount of air to enter the lungs, don’t try to fill them completely. A thumb full of air as Lamperti said. Or just the breath you use when you need to say something important.