During sleep upper airway resistance increases proportionally with a slightly diminished air flow. This can however be compensated for by increasing inspiratory force that further aggravates airway collapse and resistance. Apnea during sleep results from an interaction between the different respiratory and pharynx muscles. Sleep modifies the activity of these muscles leading to increased resistance and muscle fatigue, then eventually histological modifications. Electrical activity is not always proportional to the generated force and muscle shortening, so the effect is not always an increased permeability. In apneic patients, the efficacy of these muscles is preserved but tissue response may be poor. Histological adaptations are variable and depend on the level of the pharynx and the variability of the site of obstruction. This raises the question of electical stimulation of certain muscles and the choice of the site of stimulation.