Activity of selected rostral and caudal hyoid muscles in clinically normal horses during strenuous exercise.

The research examines the workings of certain neck and throat muscles in horses during vigorous exercise. Specifically, the focus was on the phase and quantity of the electromyographic activity of said muscles.

Research Method

• Seven clinically normal adult horses, two Thoroughbreds and five Standardbreds, were selected for the study.
• The researchers implanted bipolar electrodes surgically in the genioglossus, geniohyoideus, hyoepiglotticus, omohyoideus, sternohyoideus, sternothyroideus, and thyrohyoideus muscles of these horses.
• Post-implantation, the horses underwent an incremental exercise test on a high-speed treadmill.
• During the exercise period, the study measured the Electromyographic (EMG) activity, heart rate, respiratory rate, and static pharyngeal airway pressures of these horses.
• The EMG was measured as mean electrical activity (MEA). The MEA values recorded during maximal exercise were expressed as a percentage of the MEA measured when the horses were exercising at a speed of 6 m/s.

Results of the Study

• MEA was noted in the genioglossus, geniohyoideus, sternohyoideus, and thyrohyoideus muscles during expiration (external respiration or breathing out) and in the hyoepiglotticus and sternothyroideus muscles during inspiration (internal respiration or breathing in).
• The intensity of the MEA was observed to significantly surge with the intensity of exercise in the genioglossus, geniohyoideus, and hyoepiglotticus muscles.
• The MEA’s intensity showed a significant increase concerning the expiratory pharyngeal pressure in the geniohyoideus and hyoepiglotticus muscles.

Conclusion of the Study

• Once the exercise intensity reached 6 m/s, they found no significant additional increase in muscular action in the omohyoideus, sternohyoideus, sternothyroideus, and thyrohyoideus muscles.
• However, the geioglossus and geniohyoideus muscles, which affect the oropharynx’s diameter, and the hyoepiglotticus muscle, which affects the rima glottis, had activity linked with the intensity of exercise or expiratory pharyngeal pressures.
• The study concluded that the activity of the muscles that influence the oropharynx’s configuration may be crucial in understanding the pathophysiological processes related to nasopharyngeal patency, namely the horse’s ability to breathe adequately while exercising.