The geniohyoid (GENIO) upper airway muscle shows phasic, inspiratory electrical activity in awake humans, but no activity and lengthening in anesthetized cats. There is no information about the mechanical action of the GENIO, including length and shortening, in any awake, non-anesthetized mammal during respiration (or swallowing). Therefore, we studied 4 canines, mean weight 28.8 kg, 1.5 days after GENIO implantation with sonomicrometry transducers and bipolar electromyogram (EMG) electrodes. Awake recordings of breathing pattern, muscle length and shortening, and EMG activity were made with the animal in the right lateral decubitus position during quiet resting, CO₂ stimulated and inspiratory resisted breathing (80 cm H₂O/L/s) (RESIST) and airway occlusion (OCCL). GENIO length and activity were also measured during swallowing, where it shortened, showing a 9.31% change from resting length L_R and its EMG activity increased 6.44 Volts. During resting breathing, there was no phasic GENIO EMG activity at all, and GENIO showed virtually no movement during inspiration. During CO₂ stimulated breathing, GENIO showed minimal lengthening of only 0.07% change from resting length L_R, while phasic EMG activity was still absent. During RESIST and OCCL, GENIO showed phasic EMG activity but still lengthened. We conclude that the GENIO in awake, non-anesthetized canines shows active contraction and EMG activity only during swallowing. During quiet or stimulated breathing GENIO is electrically inactive with passive lengthening. Even against resistance, GENIO is electrically active but still lengthens during inspiration.