In a comment on my recent post, Steve asked what I thought of James O’Keefe’s recent TED lecture ‘Run for Your Life! At a comfortable pace, and not too far’. The short response is that I agree with O’Keefe’s conclusion that if your goal is to maximise the length of your life, the best strategy is probably to exercise regularly at moderate intensity. I also agree with a few of the specific points that O’Keefe makes, though I would not advance them in such a self-assured manner, because much of the evidence is incomplete. In fact I found his manner of presentation more fitting for a snake oil merchant than a scientist. He has presented a somewhat less dramatised version of the evidence in an article in the reputable Mayo Clinic Proceedings, though even that article contains at least one misleading inaccuracy.
There are several important respects in which his claims are misleading or simply wrong. Other bloggers (for example Michael Accad, Lawrence Creswell and Alex Hutchinson) have posted thoughtful articles that subject his arguments to evidence-based scrutiny. My purpose in this post is not point out the inadequacies of O’Keefe’s arguments, but rather to put forward my own thoughts of the evidence suggesting that training above a certain volume and/or intensity might be harmful.
The first crucial point that must be made is that the evidence on mortality shows that the more your train and the more vigorously you train, the greater your life expectancy, though the data does suggest that there are diminishing returns from a very large amount of vigorous training. The data present by Wen and colleagues in their article in the Lancet based on longitudinal data from 400,000 individuals, show first of all that people who exercise vigorously have a greater reduction in mortality rate than those who exercise moderately. However, among those who exercise vigorously, the rate of reduction in mortality risk with increasing minutes per day spent exercising begins to flatten beyond 50 minutes per day. However contrary to the message given by O’Keefe in his TED lecture, and also contrary to what O’Keefe states in his article in the Mayo Clinic Proceedings, Wen’s data does not show that the benefit peaks at 50-60 minutes per day. In fact Wen made it very clear in a response to a question by O’Keefe published in the Lancet in March 2012 that the available data reveal that the mortality was even lower among those exercising vigorously for 120 minutes per day, but of course the numbers of individuals exercising vigorously for 120 minutes per day is small. Wen quite sensibly refrained from extending the mortality graph beyond 60 minutes per day in his original article simply because the data is less reliable when based on a small number of individuals.
O’Keefe’s misrepresentation of Wen’s data in the TED talk, despite the fact that Wen had explicitly informed O’Keefe of the true situation about 8 months before the TED talk, is perhaps the most serious reason to distrust O’Keefe. However, just because O’Keefe appears to be untrustworthy does not mean that all his conclusions are wrong.
So what does the data really show us?
In my opinion, the following conclusions can be drawn with moderate confidence:
1) Exercise is associated with increased life expectancy, and at least up to 50-60 minutes of vigorous exercise per day, the more exercise you do, the lower the mortality rate. The limited available data indicates that those exercising vigorously for 120 min per day have an even lower mortality rate, but the numbers are too small to allow confident conclusions.
2) Prolonged vigorous exercise does produce changes in the heart, including an increase in the diameter of the ventricles and thickness of the ventricular walls. I reviewed this evidence in detail in my post on Micah True.
3) The increases in ventricular diameter and thickness are probably adaptive, in the sense that they make it possible for the heart to pump a larger volume of blood more forcefully to meet the requirement of a massive increase in cardiac output when running. In athletes, unlike in individuals with overt heart disease, hypertrophy is usually accompanied by a potentially healthy increase in capillary density. However, in at least some individuals, the remodelling of the heart is associated with disruption of cardiac rhythm. In particular, there is strong evidence that prolonged endurance training increases the risk of atrial fibrillation (as reviewed in my post in June 2010 and several subsequent posts). In those posts I also reviewed the evidence for increase in other rhythm disturbances, including potentially more dangerous disturbances arising in the ventricles
4) Rhythm disturbances such as atrial fibrillation increase the risk of stroke, at least in non-athletes. The question of whether atrial fibrillation produces an appreciable increase in the risk of stroke in athletes remains unanswered, though there are documented individual cases of adverse outcomes. For example, in a 9 year follow-up study of 30 athletes with atrial fibrillation, Hoogsteen and colleagues found that 3 (10%) had died; 15 (50%) exhibited continuing paroxysmal atrial fibrillation; permanent atrial fibrillation emerged in 5 (17%) ; and 7 (23%) of showed no further atrial fibrillation. Of the three deaths during the follow-up period, one was a sudden death during a race and is likely to have been due to a heart rhythm disturbance. The other two were attributed to strokes. Although Hoogsteen re-assuringly concludes that these deaths were not directly attributable to atrial fibrillation, the outcome is disconcerting.
5) In at least some cases, especially males who have run many marathons over a period of many years, there is evidence of increased calcification of the coronary arteries, potentially predisposing to heart attack (reviewed in my post of Jan 2012).
How should we react to this rather confusing mass of evidence? If your goal is simply to live a long and healthy life, the simple answer is to exercise frequently at a moderate intensity. This will produce a substantial increase in your life expectancy with little risk of adverse consequences. However, if you enjoy running, and in particular enjoy the thrill of running fast or the challenge of racing, the situation is different. From a statistical point of view, if you train vigorously for an hour a day, your life expectancy will be much greater than if you spent that time watching TV and perhaps greater even than the life expectancy of a the health-conscious runner who runs only at moderate intensity, but the data warrants more detailed inspection.
It is encouraging that the data from Wen’s study showed lower mortality risk for the small number of individuals exercising vigorously for 120 minutes per day. It is tempting to conclude that the additional health benefits from such training might outweigh the increased risk of adverse effects such as cardiac rhythm disturbances. However, we should hesitate before concluding that 120 minute per day of vigorous training causes the observed reduction in mortality. Once we are dealing with a small number of exceptional individuals, it is necessary to be very cautious in assuming the direction of the cause that generates the statistical correlation. It might be that only individuals with an extraordinarily robust natural constitution can sustain this level of training. Whatever we might conclude regarding overall mortality associated with extensive vigorous training, the inescapable conclusion is that there is a real risk of serious adverse cardiac events in a minority of individuals.
The crucial question
If we wish to continue to train extensively and vigorously, the crucial question is ‘can we do anything to ensure that we are not in the minority who suffer a serious adverse event?’ Unfortunately, the evidence is not good enough to allow absolute assurance of safety. However I think there is a growing body of evidence that helps us to avoid the circumstances that are most risky, and as a second line of defence, there are ways in which we might identify the onset of potentially serious disturbances and deal with them before they become dangerous.
First of all, what do we know about the circumstances that increase risk? For about 24-48 hours after a marathon, blood levels of troponin, which is a marker of trauma to heart muscle fibres, are elevated, and the strength of ventricular contraction is weaker. Almost certainly the heart is more vulnerable during this period. However, the evidence also suggests that these signs of trauma are transient. The heart recovers. If it is true that that the benefits of training reflect repair of transient trauma, the heart might be even stronger afterwards. So there is a very sensible way of increasing the odds in ones favour: make sure that you allow adequate recovery after a strenuous event such as a marathon. My own belief is that full recovery from a marathon raced to the limits of one’s ability, takes a period of several months.
Chris Mcdougall, who made Micah True the central figure in his book ‘Born to Run’, reports that True had done a six hour run in the Gila desert the day before he died. Anecdotal evidence suggests that True had not taken his dog with him on the fateful last run because the dog’s paws were sore from the previous day’s run. If indeed McDougal’s report is correct, I think that a plausible explanation of why True died during a mere 12 mile run is that he had not recovered adequately from a strenuous run the previous day; a run that might well have been expected to have produced transient damage to his heart. This is of course mere speculation based on anecdote. Other theories such as the possibility that he suffered from Chagas disease, which is endemic in New Mexico, must also be considered. But the point that I wish to illustrate is that if you enjoy running marathons or more extreme endurance running, you are not a hapless pawn at the mercy of statistical prediction. You can alter the odds and you are less likely to be among the minority with serious adverse outcome if you are well attuned to the need for adequate recovery.
As Dr O’Keefe emphasized in his TED talk, the likely mechanism by which extensive vigorous training might damage the heart is chronic inflammation. So perhaps the most important thing to seek is a way of identifying the development of chronic inflammation at an early stage, and alleviating it. Our current understanding of chronic inflammation remains inadequate, but there is a growing body of useful information.
Chronic inflammation is also likely to be the mechanism responsible for the over-training syndrome, discussed in my post in March 2010. There are some promising strategies for identifying both the early stage of over-reaching, manifest as sympathetic over-activity, and the more enigmatic late stage of over-training characterised by parasympathetic over-activity. Although the tests for over-training are still rudimentary, the availability of heart rate monitors that record the variability in intervals between heart beats (R-R variability) has opened the door to the possibility of early identification of the excessive parasympathetic activity characteristic of over-training. However the reliability of current procedures has yet to be established adequately. Alternatively, measurements of heart rate during exercise, such as the Lamberts and Lambert sub-maximal cycle test, are showing promise.
If over-reaching is identified in the early stage, it can be alleviated by scheduling a day or two of recovery. The more advanced stages of over-training are much more difficult to deal with, though it is encouraging that studies of animals indicate that even quite severe chronic inflammation can resolve during a sustained period of lighter exercise.
Not only are there sound principles regarding recovery from strenuous events together with a growing body of information about early identification and alleviation of over-training, but, as a second line of defence, a heart rate monitor with the capacity to record R-R intervals might also provide advance warning of transient minor rhythm disturbances occuring long before a dramatic serious disturbance. Unfortunately, here we get into sparsely charted waters where there is little good evidence to guide us. Furthermore, there is a danger that artefacts arising from poor electrode contact or other interference can confound the interpretation of erratic R-R recordings.
I still remain uncertain about the cause of the erratic rhythms I had recorded in 2009 and 2010. I am now confident that many of the oddities were due to poor electrode contact, but I am inclined to think that others, especially the sharp spikes followed by a partially compensatory pause, were likely to be premature atrial contractions. In an elderly person, premature atrial contractions are not uncommon, but nonetheless might be a warning sign. I was intrigued to note that on one occasion when I had become seriously dehydrated after being forced to make an unexpected long detour during a run through parched desert terrain, that the frequency of the sharp spikes was increased. Maybe they were artefacts due to poor contact between the electrodes and my dry skin, but nonetheless I took that experience as a warning to avoid serious dehydration in future.
I am re-assured by the fact that in the past year, during which I have followed a markedly periodized training program that has nonetheless included a greater volume of training than in any recent year and produced better race performances, I have observed fewer sharp spikes in the R-R records. While the interpretation of odd rhythms when they occur is fraught with ambiguity, the current rarity of spikes is re-assuring. Perhaps it is a consequence of more careful planning of my training. While my own anecdotal experiences prove very little, I think that they do provide grounds for further investigation of the potential value of a heart rate monitor with R-R recording capability as a screening tool to detect circumstances where vulnerability might be increased, or to identify oddities requiring further investigation.
In my younger days, I was a keen mountaineer. A few months ago when in Switzerland to give a talk, I took the opportunity to spend a few days in the mountains, and was reminded of how awe-inspiring it is to climb amid snow covered peaks. The sense of awe is all the greater when the crisp breeze chills your face and there are few sounds others than the chatter of your companions and the calls of the choughs circling in the air below you. Viewing the mountains through the glass window of an overheated restaurant surrounded by slushy snow at the top of a cable car ride offers a pale and soggy comparison. Mountaineering is intrinsically dangerous. The overt dangers are probably greater than those from the most extreme endurance events. Some of the risks are inherently unpredictable, but nonetheless, thorough knowledge, good planning, sound judgement and a small amount of highly technical equipment can do much to reduce the risks.
The comparison with running is imperfect, but the delight in executing a finely balanced move on delicate holds across a rock face, the grandeur of the summit views, and the satisfaction in knowing that you have pushed yourself to the limits of your physical and mental strength are a counterpart to the delight of running with graceful style along woodland trails and the satisfaction of racing to the limit of your physical and mental strength. I am therefore happy to embrace the risks that are involved, but nonetheless, just as I regard equipping myself with knowledge, expertise and equipment to maximise safety is part of the satisfaction of climbing, I consider that the challenge of learning how to minimise the risks is a part of the satisfaction of running well.