Enhanced training bradycardia in an elite cyclist following oral splint use

OBJECTIVES: Bradycardia is a well-known consequence of endurance exercise and is considered an indicator of cardiac efficiency. In this case report, the effect of prolonged mandibular extension on resting heart rate was examined. Recent studies have in fact shown that mandibular extension is capable of activating an autonomic response, called the trigeminocardiac reflex, which causes bradycardia and a decrease in arterial blood pressure.

MATERIALS AND METHODS: The subject is a healthy, 25-year-old competitive elite cyclist. For 14 days, after the daily training session, the athlete wore a customized oral splint for two hours a day before going to bed. The bite had a height of 10 mm. Heart rate was measured every morning with a common sphygmomanometer and compared with a previous series of measurements, under the same conditions, but without the use of the splint.

RESULTS AND DISCUSSION: Linear regression confirmed the emergence of training bradycardia in both series of measurements (r = 0.90, F = 52.99, p <0.0001; r = 0.76, F = 16.06, p = 0.002). The paired t-test then showed an average reduction of 16% in heart rate between the first and second series of recordings (p <0.0001). Incidentally, on the eleventh day the subject fell asleep with the splint and upon awakening measured a frequency value of 32 bpm. Resting heart rate recovered to mean values only on the morning of the 14th day. Using the splint results in extension of the mandibular muscles. The emergence of a vagal response following the activation of the trigeminocardiac reflex offers a possible explanation for the result obtained, presumably through a mechanism of temporal summation.

CONCLUSIONS: This case report showed a correlation between mandibular extension and resting bradycardia in an endurance athlete. Further investigations could determine its relevance to sports performance.

CLINICAL SIGNIFICANCE: In athletes, the use of oral splints should be carefully monitored to prevent the onset of excessive bradycardia and dangerous arrhythmias.

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