Mark’s writing from the old Crickles site

Twenty-one posts on the athlete’s heart by the Crickles cardiologist

Between 2017 and 2022, Mark Dayer, the consultant cardiologist with whom I started Crickles, wrote a series of posts for the old Crickles website about how the heart responds to endurance exercise, what can go wrong with it, and what the published evidence does and does not establish. That site is still online and nothing new has been added to it since June last year, so anything worth keeping has been sitting there quietly ever since. Mark’s posts are the part of it that has dated least, because none of it depends on which platform our data comes from or on which version of the Navigator was current at the time, and all twenty-one of them are now here.

They keep the dates on which they were first published, which puts them at the end of the listing on the home page rather than at the top. The quickest way to find them is the archive category, which every one of them carries and which you can click on from any of the listings. Each post is reproduced unchanged and opens with a line saying when it first appeared, together with a link to the original.

Start here. If you read only one, read Irony. A Crickles member notices that his heart rate has gone, as he puts it, mad; the trace shows a jump that is out of kilter with his power output and does not look like the flat line of a failing strap; he buys a single-lead ECG device, catches the event a few days later, and is referred for a procedure that is usually curative. Near the end Mark tells you who he is. It is the clearest illustration we have of the chain that Crickles exists to start, which runs from a pattern in device data, through symptoms the athlete can recognise, to a proper medical opinion.

How the heart works. The Basics… is a tour of the anatomy at roughly GCSE level, and it is the foundation for the rest. Coronary Artery Disease sets out the paradox that athletes carry more calcium in their coronary arteries than non-athletes and yet have fewer heart attacks. Death During Exertion explains why a fit person can die suddenly and which causes predominate at which ages. Colbrelli and arrhythmia explained (further) is the one to read if you have ever wondered which rhythm problems are dangerous and which are merely unnerving, and COVID-19, the heart and exercise covers myocarditis and returning to training.

What the evidence says. The substantial piece here is Mortality during Marathons - A Review of the Literature, which reviews eight papers, reconciles their conflicting denominators and arrives at a figure of somewhere between 0.70 and 1.31 deaths per 100,000 finishers. This careful research by Mark became the basis of the narrative review that we published two years later in BMJ Open Sport & Exercise Medicine, which extended the search and put the risk at about 0.67 deaths per 100,000 finishers. Running a Marathon - Will I die? is the shorter way in, and includes the complaint that race organisers do not keep the statistics that would settle the question. On the chronic rather than the acute risk, A New Post for 2018 discusses atrial fibrillation in professional cyclists and the sampling problem that makes it hard to interpret, More Good News If You Are… reports 900 Finnish former elite athletes who outlived their own brothers, Should I screen my kids? weighs ECG screening in young athletes against the harm a diagnosis can itself do, The Haywire Heart reviews the book of that name, and Coffee explains why the caffeine you were blaming is probably innocent.

When it happens to a professional. Mark wrote about the death of Michael Goolaerts at Paris-Roubaix twice, on the day and again after the autopsy, the second time to question the prosecutor’s use of the words heart attack, which names something specific and vanishingly rare in a rider of that age, and to set out the alternatives, of which an arrhythmia seemed to him the most likely.

From Mark’s own training. The remaining posts are an athlete’s rather than a cardiologist’s. End of the year plots his own heart rate against speed and gradient and finds his lactate threshold and respiratory compensation point sitting visibly on the curve. Can shoes make you faster? is a five-interval treadmill experiment with the heart rate and footpod data tabulated, and 46:31 is the outdoor confirmation a fortnight later. There is also Quakinghouse Lane on the ULTRA study and the three quarters of ultra-runners who would carry on even if told the running was bad for them, When will someone run Sub-2 in London, and I don’t know what to call this one., which is about medical error, the limits of clinical judgement, and why the absence of hard data is what prompted Crickles in the first place.

Two things are worth saying about reading posts of this age. The COVID-19 post reflects what was understood in October 2020 and the guidance on returning to training has moved on since, so treat it as a record of the time rather than as current advice. More generally, the medicine in all of these posts was written for a general audience and none of it is a substitute for seeing somebody about your own heart; as it says on the About page, Crickles is in no sense a medical tool. Mark does still answer questions from the Crickles community as best he can, and the Contact page will reach him.

Ian