The Runner's World theme for this week is the marathon, so I will focus on the three most common causes of severe medical illness or death in the marathon; sudden cardiac arrest, exertional heat stroke, and exercise associated hyponatremia. I call them heart attack, heat attack, and brain attack; respectively; and all need prompt recognition and rapid treatment, as “time is tissue.” While cardiac arrest makes the headlines, the data we have at Twin Cities Marathon shows heat stoke to be the more frequent (per 100,000 finishers) of the problems, especially when it is hot and humid. To put this in perspective, all three problems are relatively rare, but there are things you can do to reduce your risk.
Cardiac arrest can occur at any age, but in our database it is men over 40 who have diagnosed or undiagnosed coronary artery disease. Cardiac arrest can be the first symptom of heart problems and there is not much a runner can do about that except hope help comes quickly. The mistake that runners make is ignoring symptoms like exercise-related chest pain or pressure, racing heart, skipped beats, nausea, lightheadedness, fainting (syncope), or new fatigue. Changes in your training capacity or exercise-related symptoms should be evaluated before you race or push your training further.
Heat stroke can strike nearly anyone given the right set of circumstances. It presents most frequently in humid conditions when it is warmer than your acclimatization level for running hard. From our experiences at Twin Cities Marathon, we know that heat stroke can occur in relatively cool conditions and we know at what set of conditions the risk becomes dangerous for runners and the community. Runners should look for races that have “do not start” cut offs and should know their individual heat tolerance as it varies from person to person. There appear to be some individual risk factors like recent viral infection that make runners temporarily more susceptible to heat stroke. Bottom line is to not start the race or reduce your intended pace if it feels too hot or if you have been ill in the prior week.
Exercise associated hyponatremia occurs in 10-15 percent of runners based on studies out of the Boston and London Marathons but is symptomatic in an exceedingly small number of that group. In the marathon, this problem occurs when the combination of high water intake and low renal output produce a diluted blood serum sodium. This forces fluid to go into cells to keep the electrolyte balance equal in and out of the cells. When the cell swelling occurs in the brain, it is squeezed by the confines of the skull and the brain can push through the openings in the skull resulting in death. The mistake runners make is drinking too much water or sports drink along the course and after the finish. This is a rare problem if you are urinating freely, but during races it is common not to urinate. At Twin Cities Marathon, this problem is more frequent during our hotter races. Runners should know their approximate fluid needs and not try to over replace sweat losses. Drinking when thirsty, but not ignoring thirst, has helped decrease the incidence of this problem in endurance events.
A runner’s best defense is knowing and listening to your body. There is always another race and there is no harm in not starting the race if you do not feel right about the situation, whether the symptoms are from your heart, feeling too hot at the start, or getting waterlogged along the course.
Be smart, listen to your body, and don’t get caught by the deadly sins.