For men competing in triathlons past the age of 40, the grueling slog to the finish line could be their last.
As the average age of competitors in endurance sports rises, a spate of deaths during races or intense workouts highlights the risks of excessive strain on the heart through vigorous exercise in middle age.
Among the recent casualties: American Michael McClintock, senior managing director of Macquarie Group Ltd and a triathlete, who died at age 55 of cardiac arrest earlier this month after training.
The men's 40-to-60-year age bracket - often referred to as middle aged men in Lycra, or Mamils - now holds 32 per cent of the membership in USA Triathlon, the sport's official governing body in the US.
More fitness conscious than previous generations, their numbers in competitive races are swelling, along with their risk of cardiac arrest. Triathlons, the most robust of endurance races requiring swimming, biking and running, are also believed to be the most risky.
“People need to understand that they're not necessarily gaining more health by doing more exercise,” says David Prior, a cardiologist and associate professor of medicine at the University of Melbourne. “The attributes to push through the barriers and push through the pain are common in competitive sport, but that's also dangerous when it comes to ignoring warning signs.”
While benefits of exercise are well known, researchers now suspect that there may be a point at which exertion becomes dangerous - especially for middle-aged men who, because of gender and changes that accompany ageing, are more susceptible to cardiac arrest caused by vigorous exercise.
Cardiac arrest, which occurs when the heart suddenly stops beating, can be caused by almost any heart condition, including abnormal heart rhythm, thickening heart muscle and arteries - changes that can occur silently as healthy people age. The risk of sudden cardiac arrest, which can be brought on with physical stress, increases with age, and men are two to three times more likely to suffer from it than women, according to the US-based National Institutes of Health.
McClintock, who died on June 2 at his home in Larchmont, New York, was an avid skier, biker and golfer. The previous September, he completed the Jarden Westchester Triathlon, his first Olympic-length event, taking less than four hours to complete the 1.5km swim, 40km cycle and 10km run.
While McClintock's death can't be directly linked to the race, USA Triathlon has noted an increase in race-related fatalities, with the highest number occurring in the 40-to-49-year age group.
The death rate for triathlons is about twice that of marathons because of increased intensity of the competition and the initial swimming leg of the events, according to a 2012 study published in the journal Mayo Clinic Proceedings.
“The swim seems to be a particularly dangerous time,” said Andre La Gerche, a cardiologist at Melbourne's St Vincent's Hospital and marathoner. “Paradoxically, in the marathon, it's the opposite: it's the last mile of the event where the vast majority of fatalities occur.”
Researchers speculate that sprinting to the finish produces a rush of adrenalin that may trigger an abnormal rhythm in runners with susceptible hearts.
'Fighting to breathe'
The swim leg of the triathlon, often held in open water, can be “extraordinarily stressful,” said La Gerche, who has also competed in more than 100 triathlons. “You have people climbing all over you. Sometimes you're fighting to breathe, and that's not something the body is used to.”
Open-water racing triggers a clash of two mechanisms of the involuntary nervous system, according to researchers at England's University of Portsmouth. A “fight or flight” response activated by physical exertion, cold water temperature or anxiety tries to speed up the heart rate and causes hyperventilation; just as the body tries to slow the heart rate to conserve oxygen in response to facial wetting, water entering the mouth, nose and throat, and extended breath-holding, the scientists say.
“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,” wrote Mike Tipton, who runs the university's Extreme Environments Laboratory, in a commentary for the British Journal of Sports Medi-cine in February.
Train to sprint
Runners should maintain their pace or slow down in the last kilometre and not sprint unless they have trained for it. That's according to the International Marathon Medical Director's Association, from a 2010 list of recommendations in response to race-related sudden deaths.
Running appears to lower the risk for mortality when an athlete doesn't exceed more than 30 kilometres a week, log more than eight to 11 kilometres per hour, or run more than two to five times a week, researchers at the Ochsner Health System of New Orleans and the University of South Carolina found in a study last year.
More than two million people participate in long-distance running races in the US each year, a number that has doubled since 2000. Even though the risk of death from marathon running is small, increased participation has resulted in a higher incidence of sudden death at the events, according to a study published in the New England Journal of Medicine in January 2012. Out of 11 million long-distance runners, 59 people suffered cardiac arrest, 51 of them men.
Causes of cardiac events in athletes vary depending on age. For those under 35, cardiovascular conditions are usually inherited. Heart incidents in older athletes can be due to coronary artery disease they don't know they have, Melbourne cardiologist Prior said.
By middle age, most people have developed some underlying early stage vessel disease, such as hardening or plaque build-up in their coronary arteries, says Kade Davison, who teaches clinical exercise science at the University of South Australia.
“If anyone is going to have a cardiac event they're far more likely to have one during exercise,” says Davison. A person is seven times more likely to have a heart incident while exercising than at rest, he says, citing a 1984 New England Journal of Medicine study.
A person's electrolyte balance changes while doing long-distance endurance events such as marathons or long cycle rides, Davison says. People might also suffer potassium or sodium depletion, or become dehydrated, which also contributes to extra stress on the heart.
Intense exercise for periods longer than one to two hours can cause over-stretching and tiny tears of the heart's tissue, says James O'Keefe, a sports cardiologist and head of preventative cardiology at the Mid America Heart Institute in Kansas City, Missouri.
This type of repeated injury over years can cause irregular heart rhythms, increased inflammation, scarring and stiffening of the arteries, he says.
Athletic over-achievers tend to think that “more is better,” though when it comes to health, “moderation is almost always best,” O'Keefe says.
As a precaution, getting a computerised tomography, or CT, scan of the heart to look for calcified plaque is a good way for endurance athletes to check if their workouts are putting their heart at risk, O'Keefe says. Yet there is no agreement on what the best strategy is for testing.
'No good test'
“The throwaway line is to consult your doctor to make sure you're fit to race,” says cardiologist La Gerche. “The only good tests depend on people having symptoms and telling their doctors. In healthy asymptomatic people, there is no good test to see if someone is at risk of sudden death.”
Those who experience a bit of chest pain or become breathless should see a doctor to check it out, especially if the discomfort occurs during training, says University of South Australia's Davison. Sudden events that occur in people who have had no previous sign of heart disease usually indicate a build-up of plaque.
When plaque ruptures, it can cause a clot in an artery, which often doesn't show up in typical stress tests of ECG monitoring of the heart's electrical activity. Clots aren't often detected until the heart becomes stressed enough to cause a rupture, causing sudden onset of chest pain, Davison says.
Screening typically would have more value in people who are new to exercise and don't know whether they have developed a disease. People who regularly exercise without any symptoms aren't likely to show any signs in a stress test, Davison says.
World Triathlon Corp., the global owner of the sport's Ironman-branded events, made changes to the swim portion of select races after an increase in competitor deaths in recent years, the company announced last month.
Events in Coeur d'Alene, Idaho; Lake Placid, New York; and Mont-Tremblant, Quebec, no longer feature a mass swim start, eliminating a long-standing Ironman tradition. Athletes at those races will either enter the water in a continuous stream through an access point, with their time starting when they cross a timing mat, or in staggered waves based on their age group.
The changes came two months after Ross Ehlinger, a 46-year-old from Austin, Texas, died during the swim portion of the Escape from Alcatraz Triathlon, and nine months after Andy Naylor, a 43-year-old member of the Hong Kong Police Force, died near the conclusion of the 3.8km swim portion of the New York City Ironman. In 2011, two competitors died during the swim portion of the Olympic-distance New York City Triathlon.
Other organisers are also taking precautions. On the last day of August, triathletes will gather on the beach of Bintan, Indonesia and participate in the MetaMan Iron Distance race. Two speedboats will be on hand to help racers in the event of a medical emergency, says spokeswoman Hollie Avil.
O'Keefe advises his patients, especially those over 45, to run no more than 30km a week, spread out over three to four days.
“That's not to say you can't get problems when you're under 45,” O'Keefe says. “But you're much more susceptible when you're over 45 because it just takes longer for your body to recover and when you hammer it day-in and day-out, it just takes a toll on your body.”