title: Activity of selected rostral and caudal hyoid muscles in clinically normal horses during strenuous exercise.
abstract: OBJECTIVE
  To determine the phase and quantitate the electromyographic (EMG) activity of the genioglossus, geniohyoideus, hyoepiglotticus, omohyoideus, sternohyoideus, sternothyroideus, and thyrohyoideus muscles of clinically normal horses during strenuous exercise.
  
  
  METHODS
  7 clinically normal adult horses (2 Thoroughbreds and 5 Standardbreds).
  
  
  METHODS
  Bipolar electrodes were surgically implanted in the aforementioned muscles, and horses were subjected to an incremental exercise test on a high-speed treadmill. The EMG, heart rate, respiratory rate, and static pharyngeal airway pressures were measured during exercise. The EMG was measured as mean electrical activity (MEA). The MEA values for maximal exercise intensity (13 or 14 m/s) were expressed as a percentage of the MEA measured at an exercise intensity of 6 m/s.
  
  
  RESULTS
  MEA was detected during expiration in the genioglossus, geniohyoideus, sternohyoideus, and thyrohyoideus muscles and during inspiration in the hyoepiglotticus and sternothyroideus muscles. Intensity of the MEA increased significantly with exercise intensity in the genioglossus, geniohyoideus, and hyoepiglotticus muscles. Intensity of the MEA increased significantly in relation to expiratory pharyngeal pressure in the geniohyoideus and hyoepiglotticus muscles.
  
  
  CONCLUSIONS
  Once exercise intensity reached 6 m/s, no quantifiable additional increase in muscular activity was detected in the omohyoideus, sternohyoideus, sternothyroideus, and thyrohyoideus muscles. However, muscles that may affect the diameter of the oropharynx (genioglossus and geniohyoideus muscles) or rima glottis (hyoepiglotticus muscle) had activity correlated with the intensity of exercise or expiratory pharyngeal pressures. Activity of the muscles affecting the geometry of the oropharynx may be important in the pathophysiologic processes associated with nasopharyngeal patency.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Samantha L
authors.initials: SL
authors.lastname: Morello
authors.forename: Norm G
authors.initials: NG
authors.lastname: Ducharme
authors.forename: Richard P
authors.initials: RP
authors.lastname: Hackett
authors.forename: Lorin D
authors.initials: LD
authors.lastname: Warnick
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Mitchell
authors.forename: L Vince
authors.initials: LV
authors.lastname: Soderholm
mesh_terms: D000818:Animals; D004567:Electrodes, Implanted / Q000662:veterinary; D004576:Electromyography / Q000662:veterinary; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006736:Horses / Q000502:physiology*; D001239:Inhalation; D008297:Male; D010609:Pharyngeal Muscles / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*