Introduction: The chest wall is composed of two primary components: the rib cage and the abdomen. In healthy adults, these two mechanisms are coupled during both breathing at rest and speech breathing. However, with regards to infants the coupling that is observed in adults is not yet present in infants. Little is known about when during human development the coupling of the two components occurs. This study explored the contribution to chest wall movement that each component plays during single-syllable utterances by infants around the first year of life. Methods: Vocalizations and breathing kinematics were recorded from 10 infants between 9 and 16 months of age during vocal play with their mothers. The movement of both the rib cage and the abdomen were measured during production of single-syllable utterances. The relative contributions of the rib cage and abdomen were compared to see how they impacted chest wall movement during utterance production. Contributions were measured as a percentage of total chest wall movement. Results: For the infants in the study, it was determined that the abdomen contributed to a greater degree than the rib cage during the total respiratory cycle and the inspiratory phase, and that both the rib cage and the abdomen contributed to differing degrees during the expiratory phase. Discussion: The findings relate the role of the rib cage and abdomen to total chest wall movement during utterance production. This study adds information about how breath support for utterance production develops during infancy. By studying further this particular aspect of chest wall development, knowledge may be gained that could aid in the early identification of infants who might be developing atypically.