Some disorders of the upper airway in humans are marked by decreased cross-sectional area and increased airway wall compliance. Based on our observations from studies performed in the isolated upper airway of dogs, we hypothesized that the size, and perhaps the geometry, of the airway was altered by changes in the relative activation levels of various muscle pairs. This could be accomplished either by altering the intensity of the neuromuscular input, or by activating muscle pairs which have different geometric orientation to the airway. We developed an analytic relationship to allow us to vary the stimulus level driving any one of six muscle pairs, each with a different anatomic orientation, to evaluate the relationship between those parameters and upper airway volume. With data generated from bilateral electrical stimulation of upper airway muscles, we described a shape factor which allowed us to predict the maximum force produced at optimal length. These findings were applied to a length/tension curve common to striated muscle to allow us to examine the muscle behavior at lengths other than optimal. The position of each muscle was described in spherical coordinates relative to an elastic cylinder, which represented the isolated, sealed upper airway. These coordinates defined the direction in which the force generated by each muscle pair would be applied. Three compliance constants determined the change in airway dimensions produced by the muscle force. This system and its variables were used to calculate the change in volume of the sealed upper airway chamber resulting from muscle contraction. We evaluated the effect of muscle contraction on the change in upper airway volume and found good correlation between the simulation results and the changes generated by the electrical stimulation of the muscles in the isolated, sealed upper airway preparation in dogs. By changing the values for the compliance variables, one can mimic the floppy upper airway associated with sleop apnea. By changing the level of muscle activation, one can mimic the increased efforts associated with emphysema. These findings are applicable to several clinical situations including obstructive sleep apnea and electrical stimulation of the diaphragm as well as maneuvers for enhancing voice training.