The frequency of very high heart rates
A standard guideline for your likely maximum heart rate is 220 – your age. For example, someone aged 40 would be expected to have a maximum heart rate of about 180 bpm. Contrary to my belief before I started learning more about this, there is no evidence that maximum heart rate increases with fitness. It is therefore surprising to see how often heart rates much higher than this rule predicts appear on our Garmins.
In the Crickles cohort, which currently includes six women and 34 men, the maximum heart rates each of us has recorded on a Strava activity are as follows:
Since none of us (to my knowledge) is younger than 20, it is surprising that the majority of us have recorded heart rates of over 200 and for many of us our Garmins have at least once shown a heart rate much higher than that.
Should we be worried? The first thing to say is that the vast majority of these high heart rate readings are, we believe, strap errors. We now have access to well over 10,000 Strava activities on which the athlete used a heart rate monitor. Almost exactly 10% of these activities include a heart rate of 200 or greater. However, when we filter this to activities in which the high heart rate is reasonably sustained, it boils down to only 65 (at the time of writing). If the heart rate monitor always gave true readings, at least most of these 65 activities would warrant further examination. One third of the Crickles cohort has at least one of them to their name, and it’s fair to suppose that the Crickles group is reasonably representative of the community of very active amateur cyclists and runners.
However, our sports heart rate monitors do not always give true readings! So how do we know whether a reported heart rate of, say, 225 bpm reported on our Garmin corresponded to our true heart rate or was an error from the strap? This is a question to which Mark, the Crickles cardiologist, and I have paid much attention. Let’s look at three examples…
First, here’s a recent activity of my own. Paula and I were cycling up and down the central mountain of La Gomera in the Canary Islands and my Garmin showed this:
On the ascent, it shows my heart rate as rock steady on 215 bpm. It stays at that level for the start of the descent, while we freewheeled to a cafe a little way down the hill. There, with my Garmin still showing 215 bpm, Paula took my heart rate at my wrist and found it to be 70 bpm. After our coffee stop, on the remaining descent the heart rate shown on my Garmin rose further and then fell but was still displaying over 170 bpm when we got to sea level. There, I swapped my strap for Paula’s identical Wahoo Tickr, which reported my heart rate to be half of what my own strap showed. This is a clear and complete strap failure!
Here’s our second example:
We see that the rider began on an easy downhill and yet his heart rate is very quickly being reported at around 250 bpm. Just after 10 minutes there’s another spike but still the cyclist has put in little effort and again it’s on a downhill stretch; also this one is short-lived. We see many spikes like this and ascribe them to probable contact errors with the strap: the athlete may well not have built up a sweat yet and there could well be a fluttering effect on the descent. We see a third spike at just over 30 minutes. This occurs at a time of greater wattage but is also short-lived.
Here’s our final example:
This time the athlete is progressing up a renowned arduous climb when at almost two hours into the ride his heart rate rapidly rises and stays in a range of around 200-220 bpm before rapidly falling again. While nothing is certain with sports equipment, this does not have the appearance of a strap error and merits attention from the athlete.
When we first started Crickles we classified heart rate spikes by coding rules that encapsulated the patterns that we saw. Now that we have much more data we can use techniques of data science. The original rules have been decommissioned and now heart rate spikes are classified fully algorithmically. Does it work? It’s a developing art but already the algorithm can pick out the most concerning spikes, group together the spikes that look like contact errors and identify that the complete strap failure of our first example stands apart from all the other spikes. It also groups together other patterns that I haven’t covered here reasonably well. In short, it can analyse well over 10,000 activities, find the sustained heart rate spikes and group them as well as a lay human eventually could – all in a couple of seconds.
The work currently in hand is to improve the machine classification of spikes to capture more of Mark’s expert insight and fully utilises all of the data available in the Strava records. If everyone was a cyclist with a power meter and a reliable heart rate strap that would be much easier, but we cater for runners and rowers too and sports straps just don’t come with medical-grade quality. We can already see that algorithms are better able to disentangle these factors than humans, especially as the volume of data increases.
It would be great to have more athlete data. For example, we so far have only one complete strap failure like the first case above. While the algorithm can easily identify it, if we had five times the amount of data and five complete strap failures we could be more confidant that the machine would correctly identify them every time. The best way you can help us is to encourage more people to sign up, either from the sidebar on this site or directly via signup.crickles.org.
When high heart rates matter
A different kind of question is how we should alert Crickles athletes to spikes that merit further attention. Currently I do this informally – but I don’t even have contact details for everyone who has signed up to Crickles. I cannot foresee that we will post such information online, at least while we have a fully open platform. It’s an important question because this analysis may potentially flag the occasional issue at a stage when it can be addressed through a reasonable change in the athlete’s exercise programme but that may later require a more dramatic decrease in exercise and/or a medical solution.
Until we have a way to communicate information about spikes, please feel free to get in touch through the Contacts page (or directly) if you have any concerns about your own high heart rate readings.
For the large majority of athletes we’re likely to find no cause for concern in most high reported heart rates. Health issues aside, continually improving the Crickles data cleaning logic will help us to keep producing better quality training metrics than are available from all the platforms that overlook the problem.