[Editor’s Note: This article was written by Tracy Høeg, MD.]
Each year, the American College of Sports Medicine (ACSM) holds a meeting where physicians and scientists learn about the latest developments in the field of sports medicine. It is the largest, most comprehensive sports-medicine conference in the world. This year, I was presenting my group’s research on vision loss during ultramarathons and was grateful to have an excuse to attend.
This article is the first part of a two-part series. In addition to ACSM, I will be reporting from the Medicine & Science in Ultra-Endurance Sports conference that will take place in a couple weeks at the Western States 100.
Without further ado, here are selected dispatches from the 61st annual ACSM meeting held in Orlando, Florida from May 27 to 31, 2014.
Endurance Exercise and the Immune System
Over the last couple years, there has been increased interest in the immune system among the ultra community. Joe Uhan has written about the risk of infection in Overtraining Syndrome. But what if you don’t overtrain? What about ‘just’ running an ultra or a marathon once in a while? How does that change our immune system and risk of getting ill? More importantly, what can we do to stay healthy?
At this year’s ACSM meeting, Dr. Neil Walsh gave a lecture entitled “Environmental and Nutritional Extremes: Immune Function.” Dr. Walsh is from The University of Bangor in Wales and is the director of the Extremes Research Group. He co-authored the book Exercise Immunology. He had no conflicts of interest to disclose.
While doing research for this talk, I learned exercise immunology is far from a new field. Already in 1902 Dr. Ralph Larrabee found an increased white-blood-cell count (an immune-system reaction) in all six runners he studied following their completion of the Boston Marathon. More recent research at Western States indicated that 25% of runners develop symptoms of an upper-respiratory-tract infection (URI) such as a common cold in the two weeks after finishing the race (Nieman, 2003). The same study found that the lower our pre- and mid-race IgA levels (a marker of our external immunity, found in the mouth and gastrointestinal (GI) tract), the more likely we are to have these symptoms (Nieman, 2003). In other words, those who go into the race with a compromised immune system or whose immune system is affected early on are more likely to experience illness afterwards. The body produces less IgA during periods of chronic stress or intense training (Walsh, 2011a).
Dr. Walsh started his talk by introducing a study done by Peters and Bateman at the Comrades Marathon in 1983. They reported that the longer the race, the more likely runners are to report symptoms of infection in the two weeks following. 70% of those who ran the 90k race reported URI symptoms. In contrast, only 30% of the runners in the 56k race and 10% of controls reported symptoms. Essentially, the harder/longer the race, the more likely we are to have symptoms of infection. That those running the longer (90k) race were more likely to experience symptoms suggests it is not travel and/or lack of sleep alone that produces symptoms; if that were the case, there would have been approximately the same incidence of symptoms in both groups.
But (and this is a strange concept), just because you report symptoms of an infection does not mean you are actually infected. In fact, in one study, only 1/3 of athletes who experience infection symptoms following a race tested positive for a virus or bacteria out of a very extensive testing battery (Spence, 2005). The cause of remaining 2/3 of the symptoms is not well defined, but seem to come from various sources, including allergies and our body’s reaction to racing. (For example, IL-6, which can cause fever, is released from our muscles after periods of hard exercise (Pedersen, 2008).)
Dr. Walsh reviewed the reasons endurance athletes may have an increased risk of infection:
- Racing. As mentioned above, intense exercise decreases our immune response (Walsh, 2011a), but he mentioned that moderate training, even at the elite level, seems to decrease the risk of infection compared to sedentary controls (Malm, 2006).
- Heat. Exercising in high temperatures (Shephard, 1998). (Whereas passive heating–such as saunas–actually decreases our risk of infections (Ernst, 1990).)
- Cold Either cold body temperature or just a cold nose (Eccles 2002; Johnson, 2005).
- Altitude. Ascending to 3,800 meters causes a lowered immune response (Oliver, 2013).
- Malnutrition. If you are low on calories, your lymphocyte count (part of your immune system) is lowered (Diment, 2012).
- Poor sleep (Walsh, 2011b).
So, what can we do about it?
- Eat or drink carbohydrates while racing. This appears to help restore our immune system. (Dr. Walsh mentioned IgA levels specifically.)
- Wash your hands.
- Wear masks in cold air. (Think hotels or airports with extreme air conditioning systems.)
- Avoid touching your eyes, nose, and mouth.
- Consider taking probiotics. (They lower the rate of upper-respiratory and GI infections.)
- Sleep more! (See Caldwell and Dunican’s iRunFar article on the importance of sleep in performance.)
Are there substances we can take to boost our immune system pre-race?
- Vitamin D (specifically from the sun)
But not necessarily these:
- Vitamin C. Supplementation may blunt healthy effects of exercise (Ristow, 2009); evidence that it is an effective immunostimulant pre-race is thin.
- Vitamin D. Pill supplementation may blunt responses to training.
- Zinc in high-enough doses can lower immune response.
There is no good evidence for:
- Colostrum (antibody-rich cow’s first milk)
Dr. Walsh pointed out that the immune system is constantly trying to strike a balance. When it overreacts, you get inflammation, atherosclerosis, and auto-immune diseases. There is good evidence that exercise lowers inflammation and symptoms of autoimmune diseases. However when the immune system underreacts, for example due to a hard exercise effort, we have tipped the balance and increased our risk of infection.
For a physician who has dedicated his career to studying altitude training, it was refreshing to hear Dr. Benjamin Levine essentially conclude that high-altitude training only rarely improves athletic performance and only under very specific circumstances.
Dr. Levine is a distinguished professor of Exercise Sciences at the University of Texas Southwestern. He received his Doctor of Medicine from Harvard Medical School and did his residency in Internal Medicine at Stanford University. He is the cardiac-unit director for NASA and has been honored by the U.S. Olympic Committee for his contributions to the understanding of altitude training. He had no conflicts of interest to disclose.
There was a great deal of interest in altitude training following the 1968 Summer Olympics in Mexico City (elevation 2,400 meters). Exercise scientists were surprised to see altitude-adapted athletes beating athletes who normally would have won at sea level.
While studying this phenomenon during the 1970s, scientists discovered, on average, athletes’ VO2 max would increase after training a week or more at altitude and returning to sea level.
Dr. Levine went through over 30 years of research, which included much of his own work. He has, for example, been credited with proposing the concept of “live high, train low.”
Here is what we currently understand about altitude’s effect on human endurance performance:
- Altitude increases VO2max by increasing our red-blood-cell mass, stimulated by excess erythropoietin (EPO) production (Wherlin, 2006).
- Altitude training, if done correctly, will only help in sports that are dependent on VO2max (think 5,000 meters in running) and makes no difference in sports like swimming.
- In order for altitude to have an effect on your VO2max and performance, you need to be at altitude for at least 12 hours a day (Wilber, 2007a).
- From a practical standpoint, altitude tents may not work. A randomized, double-blinded, controlled trial where athletes spent 16 hours a day in an altitude (nitrogen) tent resulted in no difference in performance or blood tests compared with controls (Siebenmann, 2012), possibly because lying around in a tent for so many hours (16) a day prevented the expected physiological changes.
- The most important element of altitude training is the training. If you can’t train your intervals well, there is no point in altitude exposure (Levine, 1992).
- Athletes new to altitude appear to not run intervals as effectively and do not experience significant improvement. This is where the “live high, train low” philosophy comes from and is extensively backed by research, including that of Dr. Levine (Levine, 1992).
- Because traveling to a lower altitude multiple times a week for harder workouts is expensive and impractical, the current format adopted by elite American coaches and athletes is to live and train at altitude, but perform the hardest workouts with supplemental oxygen. [Author’s Note: I have seen discussion of this training inducing more injuries and requiring longer recovery time (Pfitzinger, 2000).]
- Non-responders. Not everyone responds to altitude exposure. The most notable example is people with iron-deficiency anemia (Levine, 1992). [Author’s Note: Rasmus Høeg, my haematologist husband explains, “Your EPO production is already high when you have iron-deficiency anemia; you can’t make it go higher with altitude.”] There is an additional subset of people (up to 50%) who are non-responders to altitude (de Paula, 2012) and it is currently unknown exactly why, though Dr. Levine noted that beyond anemia, there is evidence for a genetic component to some of these cases.
Dr. Levine suggested at the end of his talk that perhaps the reason there is so much interest in the field of high-altitude medicine and science is that even researchers love spending time in the mountains. :)
[Author’s note: Dr. Levine did not cover how much living at altitude helps for races at altitude or how long it takes to adapt. Because I know there is interest in this subject among iRunFar readers, I have included an evidence-based table (Chapman, 2013) below to help with your upcoming races at altitude:
IHE refers to exposure through an altitude (nitrogen) tent and a review of over 40 studies on this subject found no clear advantages of the tent beyond decreased shortness of breath (Wilber, 2007b).]
The Endurance Athlete’s Heart
Dr. Aaron Baggish gave, in my mind, the most outstanding talk of the conference when he went through the history of research of the effect of endurance exercise on the heart. Dr. Baggish will probably forever best be known as the medical director of the tragic Boston Marathon in 2013. He is also the director of the Cardiovascular Performance Program at Massachusettes General Hospital and he’s a runner.
And that is probably his only bias, that he loves to run. But he was very open about that and reported no other conflicts of interest.
Dr. Baggish presented over 10 epidemiological studies that indicated the more you exercise, the less likely you are to die sooner or develop life-threatening diseases. In some of these, the more you exercised during the week, the better. In some, a moderate amount was the best, but even sedentary was never better than “extreme.”
Dr. Baggish made the good point that everyone expects exercise to be like any other medication–the “right amount” is good, but too much is toxic. But this model has not panned out for exercise. And in fact, the current “normal,” which is being sedentary, appears to be the least healthy and perhaps “toxic,” if you will, in terms of what the body can handle.
Below is just one sample (Wen, 2011) from the studies Dr. Baggish cited. Their data (Wen, 2011) suggest the more you exercise, the less likely you are to die sooner, develop cancer, cardiovascular disease, or diabetes.
Given the overwhelming evidence that exercise is healthy, what has caused the recent concern in the press?
- The Missouri Study found 50 long-term male marathon runners had a higher amount of coronary-artery plaque than their age-matched controls (Schwartz, 2014). Baggish says this should be interpreted with caution because it was not a well-controlled study. He says that runners tend to have had heart disease in the family, a previous history of smoking, a history of hypertension, poor diet (all things they are “running away from”), and this study did not control for those factors.
- Anecdotal evidence. When Micah True, known as Caballo Blanco in Chris McDougall’s Born to Run, died, many were quick to point to his excess running as the cause. However, Dr. Baggish showed a copy of Micah True’s autopsy, which showed an enlarged heart, which he suggested was expected for a long-distance runner like True and that there was no sign of disease. [Author’s Note: The autopsy can be viewed publicly. (Be warned, this is a full, public autopsy that contains graphic information.) Dr. Baggish disagreed with the autopsy’s conclusion of “cardiomyopathy.” Upon reviewing the autopsy, I am not certain what the significance of the small areas of “inflammatory infiltrate” is in the heart and lungs.]
- Following marathons, multiple studies have measured the heart’s distress through lab tests called cardiac enzymes, which are found to be elevated during a heart attack. Invariably, runners emit these enzymes after marathons and longer races, which concerned many physicians and scientists. However, in the context of running, this has not been associated with death or disease and the significance of these enzymes in athletes is not currently understood (Siegel, 1997).
- Enlarged hearts. Even in 1899 and probably earlier, there was evidence that athletes’ hearts were different. Both in America and Europe there were reports of very large hearts in athletes. Baggish described that the heart remodels with repeated endurance exercise so that it becomes larger (eccentric hypertrophy, to be exact) and better at relaxing. In essence, the endurance athlete’s heart becomes more effective. However, there is a small part of the heart (between the right and left ventricles) that gets stiffer and seems to build up scar tissue over years of exercise. [Author’s note: This has also been seen in ultramarathon runners (George, 2011).] The exact significance of this is not known, but it may lead to number 5.
- Irregular heartbeats. This is, indeed, the one concern that has been shown to be true in multiple studies–that atrial fibrillation and atrial flutter, related types of irregular heart rhythms, are more common in older (middle-aged and older) male athletes (Claessen, 2011; Myrstad, 2013). This is not that feeling you get infrequently, that your heart is skipping a beat, your chest gets tight, and you feel panicky. Those are premature ventricular contractions and are normal. Atrial fibrillation sometimes goes unnoticed in older populations, but would generally be experienced as an inability to exercise (fatigue and shortness of breath). The increased risk of atrial irregular rhythms was not found in younger athletes (Pelliccia, 2005). The most likely explanation for this seems to be the larger size of the right atrium, possibly reacting to that “stiffer” area of heart muscle described above.
[Author’s Notes: 1. I could not find any studies demonstrating an increased risk of atrial fibrillation in older female endurance athletes. 2. Atrial flutter and fibrillation can be diagnosed with an electrocardiogram (EKG).]
Dr. Baggish gave the following advice for endurance athletes:
- It is not appropriate to be unhealthy in your other habits (diet, sleep, smoking, excess alcohol, etceteras) just because you run.
- Plan annual periods of recovery (less exercise, “off season”).
- Warm ups and cool downs. Though sudden cardiac death is excessively rare, a proper warm up will help reduce your risk.
- Careful event preparation. Know what kind of race you are getting into and train appropriately.
- Respect a virus. (Drop your hard workouts if you are sick.)
- Listen to warning signs. [Author’s Note: In my clinical experience, athletes are generally the best population at noticing something is “off.” If you are worried, get it checked out! If the doctor ignores your complaint, get a second opinion.]
[Author’s Note: None of the studies Baggish referred to was a randomized-controlled trial, so it is impossible to determine cause and effect. It is, however, very important that people not be discouraged from starting an exercise program due to theoretical concerns at the extreme end of the exercise spectrum. Finally, with growing interest in ultramarathon medicine, it will be interesting to follow the work of Dr. David Oxborough (who will be speaking at the Western States conference) and others who do cardiac studies specific to ultra-endurance athletes. Currently the amount of exercise that is considered “extreme” has not been well-defined and it’s therefore difficult to know exactly which studies and findings apply to ultramarathon runners.]
Call for Comments (from Meghan)
- What are your thoughts on any or all of these dispatches? On endurance exercise and the immune system, altitude training, and the endurance athlete’s heart?
- Have you experienced symptoms of an upper-respiratory-tract infection after a long ultra?
- How does your body react to altitude?
- What are your thoughts on Dr. Baggish’s discussion of endurance athletes’ heart health?
I would like to thank Meghan Hicks, Rasmus Høeg, and Joan and Don Prachthauser for their editorial help with this article.
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