Investigation into pathophysiology of naturally occurring palatal instability and intermittent dorsal displacement of the soft palate (DDSP) in racehorses: Thyro-hyoid muscles fatigue during exercise.
Authors: Cercone Marta, Olsen Emil, Perkins Justin D, Cheetham Jonathan, Mitchell Lisa M, Ducharme Norm G
Journal: PloS one
Summary
# Editorial Summary: Thyro-hyoid Muscle Fatigue and Dorsal Displacement of the Soft Palate Intermittent dorsal displacement of the soft palate (DDSP) remains a frustrating cause of exercise-induced airway obstruction and performance loss in racehorses, yet its underlying mechanism has never been fully understood. Cercone and colleagues implanted intramuscular electrodes into the thyro-hyoid muscles of nine racehorses—four with naturally occurring DDSP and five controls—and used telemetric electromyography to monitor muscle activity during incremental treadmill exercise tests, analysing both mean electrical activity and power frequency distributions through wavelet decomposition. Horses with DDSP exhibited significant muscle fatigue at maximal exercise intensity, characterised by decreased electrical activity, reduced median power frequency, and progressive loss of high-frequency wavelets, which are electrophysiological hallmarks of muscle fatigue. These findings suggest that thyro-hyoid muscle fatigue is the primary mechanism underlying palatal instability during high-speed exercise, rather than anatomical defect alone. Clinically, this opens new avenues for performance management—beyond conventional surgical interventions—including targeted conditioning programmes, consideration of fibre type composition in breeding decisions, and investigation of metabolic support strategies to enhance fatigue resistance in the laryngeal muscles responsible for maintaining airway patency.
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Practical Takeaways
- •Thyro-hyoid muscle fatigue appears to be a primary mechanism in exercise-induced DDSP; training programs should consider muscle conditioning and fatigue resistance in affected horses.
- •Palatal instability alone does not always manifest as clinical DDSP; individual variation in muscle fatigue response may explain why some horses show intermittent versus consistent displacement.
- •Future management strategies may benefit from identifying fiber type composition and metabolic characteristics of thyro-hyoid muscles to target conditioning or identify predisposed individuals.
Key Findings
- •DDSP-affected horses (n=4) demonstrated thyro-hyoid muscle fatigue at high exercise intensity, characterized by decreased mean electrical activity and median power frequency on electromyography.
- •Palatal instability persisted after surgical electrode implantation in all four DDSP-affected horses, but only two horses demonstrated actual palatal displacement post-surgery.
- •Wavelet decomposition analysis showed progressive decrease in high-frequency contributions in DDSP horses during intense exercise, consistent with muscle fatigue patterns.
- •Control horses (n=5) with normal upper airway function did not show electromyographic evidence of thyro-hyoid muscle fatigue during incremental exercise.