Puzzling as it is for many people unaccustomed to this logic (typically, those people prone to assume that if 1 drink is fun, 20 must be fucking hilarious), biology has a sweet spot for everything.
Biology is all about the just-right of Goldilocks’ porridge. This doesn’t mean the oft-quoted “everything in moderation” is true, especially since one often hears this from people whose bodies bear witness to the fallacy that Cheetos, Jack Daniels and cigarettes “in moderation” produce optimal physiological function. I am also not aware that, say, asbestos or PCBs “in moderation” are beneficial.
It means that there is a right amount — usually a range — for everything. It may indeed be moderate. It may be large. Or it could be a tiny microgram.
In this case, endurance exercise. How much is too much? There is accumulating evidence that while some is good — say, a nice half-hour’s run outside on a sunny day — running marathons may not be the brightest idea for the average person.
The frequency of cardiac incidents (i.e. keeling over as the ticker goes on strike) decreases with some exercise, but increases with a lot of endurance exercise, as many unfortunate (and late) middle-aged marathoners who are myocardially infarcting all over the finish line can attest.
As one study notes:
Conventional cardiovascular risk stratification underestimates the CAC burden in presumably healthy marathon runners. As CAC burden and frequent marathon running seem to correlate with subclinical myocardial damage, an increased awareness of a potentially higher than anticipated coronary risk is warranted.
Möhlenkamp S, Lehmann N, Breuckmann F, et al. Running: the risk of coronary events : Prevalence and prognostic relevance of coronary atherosclerosis in marathon runners. Eur Heart J. 2008 Aug;29(15):1903-10.
On the other hand, as another study points out, “Vigorous exercise (running) at middle and older ages is associated with reduced disability in later life and a notable survival advantage.”
Again, sweet spot. Some is good. A fair bit is good. A lot, not so much.
A recent study examines one mechanism by which this problem may occur.
This study collected blood from sedentary volunteers and triathletes at rest and after a short-duration triathlon (SDT) and after a long-duration triathlon (LDT-half Ironman) competitions.
It found that the triathletes had depressed immune systems and more cellular damage, both at rest and after events.
In addition, when cell death occurred, in SDT it was more likely be from apoptosis (a kind of pre-programmed cell suicide that is often part of a natural process of healing). In LDT it was more likely to be from necrosis (aka cell murder).
The post-event triathletes also had very high reactive oxygen species (ROS), akin to “rusting” in the body. ROS can induce damage to cellular DNA and other structures.
[There was] “lowered lymphocyte proliferation capacity compared with sedentary volunteers either at rest or after the competitions…. Lymphocytes from triathletes after SDT competition showed an increase in DNA fragmentation, phosphatidylserine externalization, and mitochondrial transmembrane depolarization and did not alter membrane integrity when compared with cells from athletes at rest. In contrast, the LDT competition raised the proportion of lymphocytes with loss of membrane integrity when compared with cells from athletes at rest and did not change the apoptotic parameters. The LDT competition induced an increase of reactive oxygen species (ROS) production by lymphocytes compared with triathletes at rest. The SDT competition did not alter ROS production by lymphocytes when compared with cells from triathletes at rest. ROS production by lymphocytes after LDT competition was 60% higher than in SDT.”
Levada-Pries, Adriana, et al. Induction of Lymphocyte Death by Short- and Long-Duration Triathlon Competitions. Medicine & Science in Sports & Exercise. 41(10):1896-1901, October 2009.
Temporary immunosuppression is normal following nearly all exercise, and is likely part of the normal process of supercompensation (getting stronger/better/more functional after an exercise stimulus). But again, sweet spot.
It’s like a little life challenge is good — obstacle is presented, you struggle through, learn life lessons, become tougher and more resilient. But a huge, traumatic life challenge = years of therapy and PTSD.
Are triathlons bad? Am I a big meanyhead to endurance athletes? No. Each person finds their own exercise path.
However, if you experience symptoms of significant immunosuppression and tissue damage following extensive bouts of endurance exercise, and you’re feeling like a rusty old car, perhaps consider scaling back.