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If increased effort is needed to fill the lungs, supraclavicular and infraclavicular retraction may be seen. In infants, sternal retraction occurs with only a slight increase in respiratory effort, the result of the pliability of their chests. Compare intercostal bulging.
During breathing, these muscles normally tighten and pull the rib cage up. Your chest expands and the lungs fill with air. Intercostal retractions are due to reduced air pressure inside your chest. This can happen if the upper airway (trachea) or small airways of the lungs (bronchioles) become partially blocked.