The purpose of this study was to assess normal values of thoracoabdominal motions (TAM) during spontaneous breathing and vital capacity (VC) maneuvers in relation to sex, age, and body position. For this, 120 healthy subjects from 10 to > 60 yr old were studied using the respiratory inductive plethysmograph (Respitrace). The volume-motion coefficients obtained during quiet breathing for the rib cage (RC) were almost twice those for the abdomen (ABD) and were not influenced by sex or age and also not by posture, except for the increased ABD coefficients in the supine posture (p < 0.05). Under most conditions RC motion predominated over ABD motion, except quiet breathing in the supine position. Sex-related differences in TAM were not found during quiet breathing, yet during VC maneuvers the women were slightly more RC breathing (p < 0.01). Age-related differences were also only significant during VC maneuvers: men of more than 50 yr old especially became less RC breathing. Posture had a very significant effect (p < 0.001) during quiet breathing as well as during VC maneuvers: the RC predominance was greatest in the standing posture and least in the supine posture. During VC maneuvers the subjects became more RC breathers than during quiet breathing (p < 0.001). The X-Y coordinates of RC motion (on the Y axis) versus ABD motion (on the X axis) showed under all conditions a counterclockwise looping during the breathing cycle: the looping was elliptic during quiet breathing but was more irregular and variable during VC maneuvers, and this also depended on body position.(ABSTRACT TRUNCATED AT 250 WORDS)