The study found no clinically significant restriction of the physical mechanisms for breathing when healthy subjects were placed in the PMRP with up to 90.2 or 102.3 kg of weight on their backs. Also, when subjects were struggling against the restraints for 60 seconds while in the PMRP, there were no clinically important limitations of breathing mechanisms. These findings suggest that factors other than the restriction of breathing processes should be considered when determining the causes of deaths while persons are under PMRP in the field. Thirty volunteer male and female subjects were recruited for the study. Persons were excluded if they had any history of pulmonary or cardiac disease, current recreational drug use, or other significant illness or disability that would limit their ability to perform the exercises required for the study. Maximal voluntary ventilation (performance of the breathing mechanism) was measured in seated subjects, in the PMRP, and when prone with up to 90.1 or 102.3 kg of weight on the back. When in the PMRP, an individual is prone with his/her wrists secured behind the back; ankles bound together; and wrists and ankles tied together with handcuffs, cords, chains, or hobble devices. 3 tables, 2 figures, and 27 references