Why do healthy swimmers die?

Why do healthy swimmers die?

Deaths of seemingly healthy athletes during competitive open water swimming could be explained by research.

Scientists at the University of Portsmouth are looking into why more athletes die during the swim compared to the cycling or running sections of a triathlon. They also want to know why these swimmers die during the competition itself but not during training.

Of the 38 athlete deaths in American triathlons between 2003 and 2011, 30 occurred during the swim. None of those who died had any pre-existing health problems.

Professor Mike Tipton, who runs the Extreme Environments Laboratory in the University’s Department of Sport and Exercise Science, believes these deaths could be caused by a phenomenon called Autonomic Conflict. This is the first time this concept has been applied to competitive swimming.

Autonomic Conflict takes place when the body’s cold shock response and diving response are activated at the same time. The cold shock response speeds up the heart rate and causes hyperventilation, whereas the diving response slows the heart rate down to conserve oxygen.

In an online commentary written for the British Journal of Sports Medicine, Professor Tipton said: “Normally the two responses don’t happen at the same time, but when they do, the heart can go into abnormal rhythms, which can cause sudden cardiac death.”

The cold shock response can be caused by anxiety, competitiveness and the body entering cold water. The diving response is caused by facial wetting, extended breath holding and water entering the nasal passage. Although many of these factors are present to some degree during training, anxiety and competitiveness are more likely during the competition.

According to Professor Tipton, the confused mass swim in the competition, not present in training, can also require extended breath holds and cause more water to enter the nasal passage.

“The increase in these factors makes Autonomic Conflict more likely during the competition than in training,” he said.

Professor Tipton conducted earlier research with Professor Mike Shattock from King’s College London that linked submersion in cold water to Autonomic Conflict and sudden cardiac death. This included experiments using isolated rat hearts, the results of which were published in the Journal of Physiology last year. He has also conducted experiments involving helicopter underwater escape training. The results were published in the journal Aviation, Space and Environmental Medicine in 2010. He intends to do further research to determine how open swimming deaths could be prevented.

He said: “Possible solutions involve the prevention of swimmers coming together at the start or during the race, by introducing wave starts and longer distances before turns.” 


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