Fast Competitive Swimmers Demonstrate a Diminished Diving Reflex

Area of Science:

• Sports Physiology
• Cardiovascular Physiology
• Exercise Science

Background:

• Breath-holding during intense exercise, like 50-m front crawl swimming, can induce the diving reflex.
• The diving reflex involves bradycardia (slowed heart rate) and reduced active muscle blood flow.
• Maintaining oxygen supply to the brain is crucial during breath-holding to prevent fatigue.

Purpose of the Study:

• To investigate if faster swimmers in 50-m front crawl with limited breathing display a blunted diving reflex.
• To compare cardiac and active muscle blood flow responses between fast and slow swimmers.
• To assess if elevated cerebral perfusion counteracts peripheral and central fatigue in elite swimmers.

Main Methods:

• Twenty-eight competitive swimmers performed a 50-m front crawl time trial with minimal breaths.
• Swimmers were categorized into Fast and Slow groups based on performance.
• Physiological responses, including leg blood flow, cardiac output, heart rate, and cerebral blood velocity, were measured during maximal voluntary breath-holding knee extension exercises.

Main Results:

• The Fast group showed a delayed reduction in leg blood flow compared to the Slow group.
• The onset of bradycardia was delayed in Fast swimmers, who also exhibited a higher lowest heart rate and cardiac output.
• Cerebral blood velocity (middle cerebral artery mean blood velocity) did not differ significantly between the groups.

Conclusions:

• Competitive swimmers with superior 50-m front crawl performance (limited breaths) demonstrate a diminished diving reflex.
• A blunted cardiac and muscle blood flow response, rather than altered cerebral perfusion, characterizes faster swimmers.
• These findings suggest physiological adaptations in cardiovascular regulation contribute to enhanced performance in breath-hold swimming.