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Obstructive sleep apnea is caused by pharyngeal occlusion due to alterations in upper airway mechanical properties and/or disturbances in neuromuscular control. The objective of the study was to determine the relative contribution of mechanical loads and dynamic neuromuscular responses to pharyngeal collapse during sleep. Sixteen obstructive sleep apnea patients and sixteen normal subjects were matched on age, gender, and body-mass index. Pharyngeal collapsibility, defined by the critical pressure, was measured during sleep. The critical pressure was partitioned between its passive mechanical properties (passive critical pressure) and active dynamic responses to upper airway obstruction (active critical pressure). Compared to normal subjects, sleep apnea patients demonstrated elevated mechanical loads as demonstrated by higher passive critical pressures ( – 0.05 cm H2O (SD 2.4) vs. – 4.5 cm H2O (SD 3.0), P = 0.0003). Dynamic responses were depressed in sleep apnea patients, as suggested by failure to lower their active critical pressures ( – 1.6 cm H2O (SD 3.5) vs. –11.1 cm H2O (SD 5.3), P < 0.0001) in response to upper airway obstruction. Moreover, elevated mechanical loads placed some normal individuals at risk for sleep apnea. In this subset, dynamic response