Your heart on a six-hour ride: what the Holter monitor saw

Long weekend rides have something magical about them: the coffee stop halfway, the chat in the group, that climb that took away even your will to talk. But what is your heart up to meanwhile? A group of researchers decided to find out by fitting amateur cyclists with a Holter monitor for nine days. Spoiler: there are things worth knowing, and none of them is a reason to hang up the bike.

How the study was done

The work, published in the Journal of the American Heart Association, followed 34 amateur cyclists with many years in the saddle: an average age of 52, seven in ten men and around 200 km of training a week. They wore a continuous electrocardiogram (Holter) for four normal days, on the day of a ride of up to six hours at a demanding intensity, and for the four days after.

What they found

68% of participants showed, at some point during those nine days, an arrhythmia the researchers classed as abnormal, and half had pairs of premature ventricular beats. The interesting part is the timing: ventricular arrhythmias shot up on the day of the long effort and went back to their usual level the next day. Atrial ones, on the other hand, stayed stable throughout.

Who was most likely to have them that day? Older participants and, above all, those who already showed arrhythmias on the previous days. The relative risk rose from 2.2 times for those who had arrhythmias on at least one day before the ride to 5 times for those who had them on three days or more.

Before you panic, breathe

An occasional premature beat is very common, in sedentary people too, and the vast majority of the time it has no consequences at all. This study does not say cycling is dangerous or that the participants had any serious event: it says that a very long, intense effort temporarily disturbs heart rhythm in many amateurs, and that this is more noticeable in people who already had some tendency to it.

It also has limitations, which the authors themselves acknowledge: the sample is small, mostly male and over 35, and not everyone completed the cardiac tests. It is a valuable clue, not a verdict.

What they do point out is a gap: in many countries cardiac screening focuses on elite athletes, while the endurance amateur, who sometimes trains almost as much, stays off the radar.

What to do if you are a weekend endurance rider

If you are over 35, train high volumes or have ever been told you have ectopic beats, a sports medical check with an electrocardiogram and, if the doctor thinks it appropriate, an exercise stress test is an investment worth more than any carbon wheel. Tell them how many hours you ride: a one-hour spin is not the same as a 200 km sportive.

And one idea to take home: the kilometres do not all have to come in the same ride. If big goals motivate you, the Hermes Challenge sets 300 km that you can build up at your own pace, spread over sensible rides, without turning every Sunday into a six-hour epic.