This method has been previously described and validated in detail.10, 15, 16, 17, 18 Briefly, a nonstretch belt (48-mm wide) with a metric tape measure fixed over it was placed over the umbilicus to measure girth; another belt was placed below the mammary glands to measure thoracic perimeter. The overlapping ends of each belt were adjusted carefully by 2 elastic bands to maintain the belt constantly adapted to the abdominal wall. Measurements were taken with the subjects breathing quietly as the average of inspiratory and expiratory determinations over 3 consecutive respiratory cycles without manipulation of the belt-tape assembly by the investigator. In the first pretreatment recording session, the location of the belts was marked on the skin for subsequent measurements. During each intervention session (biofeedback or control), the belts were kept in place for repeat measurements (at the beginning and at the end of the session).