(Top left) Representative ultrasound image of the diaphragm. The muscle thickness was measured as the distance between the inner layers of the fasciae at end expiration. The probe was located at the zone of apposition between the midaxillary or anterior–axillary line in the 8th to 11th intercostal space. (Bottom left) Representative ultrasound image of the rectus abdominis muscle. The measurement of the muscle thickness was performed at end inspiration and was performed perpendicular to the inner layer of the muscle fascia. The probe was located at approximately 2 to 3 cm above the umbilicus and 2 to 3 cm lateral from the midline. (Right) Representative ultrasound image of the lateral abdominal expiratory muscles, showing three muscles from the top to bottom: external oblique, internal oblique, and transversus abdominis muscles. The measurements of the thickness of expiratory muscles and individual layers were performed at end inspiration and were performed perpendicular to the inner side of the muscle fascia (yellow arrow). The muscle fasciae are presented as green lines. The probe for the lateral abdominal muscles measurement was located approximately on the anterior axillary line, midway between the inferior border of the rib cage and the iliac crest.