Triathlon races sanctioned by USA Triathlon are swim-bike-run events that comply with safety requirements of this national governing organization. While distances vary, the swim is the first and shortest segment. The swim venue is usually a lake, reservoir, ocean front, or river. Substantial swim training is necessary for racing sprint (750 m) to ironman (2.4 miles) distances. Triathletes typically train throughout the year, mostly in heated lap pools with lane lines that minimize physical contact between swimmers.
Review of Triathlon Swim Deaths
A committee formed by USA Triathlon in 2012 reviewed 43 cases of adults (9 women and 34 men, 24 to 76 years old) who died during sanctioned events in the United States between 2006 and 2011 (9). Five of the fatalities occurred in cycling crashes. Direct trauma was not the cause of the other 38 deaths, 30 (79%) of which occurred during the swim segment, 3 (8%) during the bike, and 5 (13%) during or soon after the run. The committee reasoned that cardiac arrest was the most likely principal cause of the nontraumatic deaths, including the swim deaths.
The 30 drowning victims did not respond to cardiopulmonary resuscitation (CPR) attempted on the scene. Curiously, a high percentage of the swim deaths occurred fairly soon after the start and in calm water. In most cases, the proximate cause of drowning was not discovered. Numerous reports in mass media have addressed the mystery of triathlon swim deaths.
The risk of participation was approximately 1.7 deaths per 100,000 race finishers (N = 2,512,761) on average during the 6 years reviewed. In comparison, a mortality rate of 0.8 per 100,000 participants (95% confidence interval, 0.5–1.1) was found for more than 3 million marathon runners over 30 years (12). However, CPR is likely started sooner and is more successful in marathon races. The disturbing statistic is that swim deaths accounted for 79% of total mortality. What predisposes trained triathletes to break down more often when swimming than running? Is it simply because the swim segment is first, or is what goes wrong specific to the swim?
Adverse swim conditions have long been a widely shared source of anxiety among triathletes. The degree of anxiety relates to the perceived chance of inhaling water from colliding with other swimmers or being swum over. Tension, even fear for some, can lead to irregular breathing at the swim start. Prerace apprehension seems more severe for mass starts than wave starts, probably because of the unavoidable physical contact. Large events are worrisome, as bigger bottlenecks form after the start and at turn buoys. Cold water, rough water, currents, deep water starts, beach run-in starts, and poor visibility can each make swim-related anxiety more severe.
Warming up in the water facilitates habituation, i.e., eases anxiety and muscle tension. Unfortunately, the swim venue is not made available for warm-up at many races. Starting without a swim warm-up can exacerbate the symptoms of hyperventilation associated with sudden water immersion. Crowding and bottlenecking early in the swim interrupt the usual breathing pattern. Splashing, waves, and collisions increase the chance of swallowing water and choking. Swim anxiety may escalate to panic if breathing difficulty does not resolve.
Swimming-Induced Pulmonary Edema
The pathophysiological mechanisms that precede triathlon swim failure and drowning remain speculative. The USA Triathlon committee implied that cardiac arrest was the most likely cause of the swim deaths, citing a previous report that various cardiovascular abnormalities were identified on autopsy in seven of nine fatalities during a triathlon swim (4). On the other hand, apparently healthy triathletes may be at greater risk of drowning from respiratory distress due to swimming-induced pulmonary edema (SIPE) (2,7,11). Documented cases of SIPE in triathletes have occurred within minutes of the swim start (2).
SIPE probably begins when excessive perfusion of the lungs ruptures some pulmonary capillary and lymphatic vessels. The hydrostatic pressure of immersion and the prone position of swimming combine to acutely increase central blood pressure and volume, thus overfilling the pulmonary vascular system (7). Peripheral vasoconstriction in cold water can further raise pulmonary artery pressure. Strong cardiac contractions induced by strenuous swimming may be the ultimate physiological factor that forces leakage of blood and plasma protein into the alveoli and small airways (6,13). The key symptoms of SIPE are dyspnea, cough, crackles, and hemoptysis. Of note, these symptoms were not found in patients with cardiac diseases with impaired systolic and diastolic function during aquatic exercise despite them having elevated pulmonary artery and mean capillary pressures (10).
SIPE slows alveolar gas exchange in affected regions of the lungs. Continuing to swim with shortness of breath will hasten the onset of respiratory distress and swim failure. Similar to cardiac arrest, SIPE-related drowning probably results from rapid loss of consciousness due to severe hypoxemia. Rescued swimmers with SIPE require supportive ventilation. Oxygen administration and rewarming are the mainstays of treatment. Symptoms of SIPE resolve within approximately 72 h, and preincident cardiopulmonary function and exercise capacity are usually recovered soon afterward (8).
Hypertension, cardiac dysrhythmias, cardiac structural abnormality, cardiac dysfunction, asthma, sleep apnea, and diabetes might be predisposing conditions for immersion pulmonary edema (2,7,11). Competitive triathletes may have uniquely elevated risk of SIPE due to their focus on racing (3). Triathletes often consume various drinks before the swim segment to ensure starting the race at full hydration. The caveat about this practice is that overhydration increases abdominal fluid volume, which may contribute to SIPE (14).
The committee did not report whether more deaths occurred at cold swim venues. As of 2014, USA Triathlon recommends that race organizers cancel or shorten the swim segment for cold water conditions, typically when the water temperature is below 53°F. Sudden immersion in very cold water without a swim warm-up may trigger prolonged cold shock hyperventilation, to a similar extent in skilled and less skilled swimmers (1). Face immersion in cold water abruptly slows heart rate, extends cardiac filling time, and increases the volume of blood pumped into the lungs with each beat. This so-called “diving reflex” has the protective effect of increasing brain blood flow. However, it also increases breath-hold time and arterial carbon dioxide tension during exercise (5). Prolonged face immersion at the start of a race may be a risk factor for SIPE because it allows swimmers to sprint further, increasing carbon dioxide retention and the drive to hyperventilate.
Triathletes are strongly encouraged to become accustomed to immersion in cold water before racing at a cold swim venue. Neoprene wetsuits provide warmth and some flotation and are allowed at cold venues. However, anxious or less skilled swimmers should not incorrectly take solace that wearing one will keep them afloat in a crisis. Wetsuits are often adjusted and tightened at the neck by a friend or another participant just before the swim start. The collar should be loosened to relieve any restriction to breathing felt in the swim warm-up.
Prevention of Dyspnea
Triathletes with irregular breathing related to swim anxiety are advised to receive coaching and, if necessary, therapeutic management. Gradual immersion and an easy swim warm-up reduce the tendency to overbreathe at the start. An active preswim warm-up onshore will promote blood flow to the extremities that could lessen the increased central blood pressure associated with immersion. Competitive triathletes commonly sprint at the start to form a pace line. However, sprinting at any time during the swim segment increases oxygen debt and for most triathletes is not an effective race strategy. A useful self-pacing swim guide is to maintain some breathing reserve. Persistent dyspnea warns of imminent swim failure. A swimmer who struggles to breathe, particularly with a cough, should immediately back-float and signal for help. Triathletes who often cough or feel breathing discomfort in swim training should have their lung volumes and flow rates tested (8).
Swim fatalities in the USA Triathlon review were not associated with racing or training experience. Sanctioned triathlon events require entrants to sign a waiver during registration. Participants could evaluate their personal readiness for the swim venue if the expected water conditions were updated on the race Web site. USA Triathlon has recently implemented an online swim safety report for race directors to submit circumstances of incidents that occurred in the swim segment.
Swim training should not be exclusively in a pool but rather include open-water swims specific for the venue, race distance, and expected water conditions. Swim practice in groups that simulate crowding and physical contact may lessen swim anxiety. Race directors should recognize that a swim warm-up has important physiological benefits and allow participants access to the venue before the start. A swim warm-up is strongly encouraged at some races, such as the Auburn Triathlon: http://www.auburntriathlon.com/swim/.
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