Heart Rate Regularity

Mark and I quite often get asked about suspicious heart rate readings by people using Crickles. Often these are probably just Garmin/strap errors: the majority of our population occasionally see heart rate values that look wrong…


The chart shows the distribution of maximum recorded heart rate by athlete. 62% of athletes show a maximum HR over 200 bpm, for 36% it’s over 220 bpm and the maximum to date stands at 365 bpm. These values are dubious. Data cleaning is therefore an important part of Crickles algorithms.

While it is not an aim of Crickles to train algorithms to give a medical diagnosis of heart problems, we do flag when activity data looks unreliable for use in quantifying the cardiac stress score (CSS). The Activities page on the Navigator now shows a new column called Diagnostic. This is only populated for activities where a heart rate monitor was used – if not, it appears blank. (It may also very occasionally appear blank for other reasons.) Where a Diagnostic value appears it will be one of the following:

  1. Check_Strap – it looks probable that there was a recording error and the heart rate data for this activity is wrong;
  2. Irregular – the heart rate data stream looks questionable but Crickles cannot reliably ascribe this to a strap error;
  3. Regular – the heart rate data is good for use in the measurement of CSS.

This algorithm that produces this diagnostic does about as good a job as I can do by eye at identifying odd-looking data streams, and (unlike me) it can do this consistently on the hundreds of thousands of activity records in Crickles. However, it is not in any sense a medical diagnosis and the appearance of only Regular values is no guarantee of good health.

When Crickles athletes email us with concerns about their cardiac health I do sometimes opine on how relatively un/usual the data may look but the medical aspects of such questions are always addressed by Mark, who is a cardiologist. Mark can look at the data in the context of symptoms, such as chest pain or fainting, and the athlete’s medical history.

To explore any Check_Strap or Irregular activities you may have, on the Activities tab you can:

  • Change the Date Range in the side panel to select the time horizon you want to explore;
  • Use the Search box on the top right of the screen to pick out Check_Strap or Irregular values;
  • Use the small triangle next to Diagnostic to sort your activities by Diagnostic.

The Regularity page has had a make-over to show the frequency with which Irregular values occur. Previously only available as a beta feature by request, this page now has two charts. The one on the right is the chart that was present previously:


This shows whether your recent aggregate heart rate pattern is different from its historical pattern. Significant changes such as that shown can be due to an intentional change in your exercise regime – for example, reducing the intensity of exercise. If the gloss at the top indicates a significant change with sufficient data for a valid comparison (as here) but you haven’t knowingly modified your exercise habits it may be worth digging in further.

This chart responds to the three checkboxes in the side panel, as before.

The left-hand chart on the Regularity tab is new:


This shows quarter-by-quarter how often you’re getting Irregular as the Diagnostic for your activities on Crickles. As with CSS, there is no firm science on what constitutes a good value but what we can do is show how you compare to the (Crickles) crowd. Values above the two orange lines, and especially the solid orange line, are unusually high.

The size of each quarterly point indicates how many activities contributed to it. A high Irregularity Ratio is less meaningful when it is derived from only a few points. As a guide, 30 points can be taken to constitute a good sample. The gloss above the chart tells you exactly how many Irregular diagnostics you’ve had in the current quarter, and, for good measure, the number of Check_Strap diagnostics (which is not shown on the chart).

If you consistently see an Irregularity Ratio above the orange lines based on a meaningful number of activities, it’s worth changing your heart rate strap. If you continue to see a high ratio, we’d be interested in hearing from you.

While Irregularity Ratio is a useful measure for data verification, there is no science that establishes an association with cardiac health. Intriguingly, a number of our active athletes have filled in the Crickles survey and, amongst these, the average Irregularity Ratio happens to be 56% higher in athletes who report a diagnosis of Atrial Fibrillation than amongst those who don’t. However, to attain significance in a statistical test – or to find that it’s a coincidence – we’d need many more people to fill in the survey. If you haven’t done so yet, please do so here. The survey is super-quick to complete and all responses are equally useful, even if you have only good health to report.

Enhancement to the Timeline tab

There is now a new feature on the Timeline tab that enables you to see the name of the activity corresponding a point on the chart. When you look at the Timeline you’ll see a new “Click on a point to see the activity name” annotation in the top left:

Timeline activity

If you single click on the centre of one of the points on the chart that annotation will instead show the activity name. You have to be quick as the name will disappear after a moment – if you didn’t catch the name you’ll have to click again!

If you never name your activities on Strava then the names you see here will be generic – “Morning Ride”, for example. The feature is only really useful if you’re in the habit of giving your significant activities meaningful names.

This feature does not, of course, work on the aggregated monthly view of the Timeline.

Enhancement to Relative CSS

When you now look at the Navigator you’ll see that the colour scheme on the Relative CSS tab (where you normally first land) has changed: the bars other than the one representing you are pink rather than blue. This reflects a change in the default methodology to include all activities and not just those for which heart rate information is available. In the absence of data from a heart rate monitor, Crickles estimates cardiac stress from a power meter if one has been used (this is a good estimate), and in the absence of both heart rate and power data Crickles falls back on an estimate based on observed averages (this a poorer estimate, but better than ignoring those activities altogether).

CSS pink

If you want to go back to the old style, giving you analysis based only on activities with heart rate data, just tick the new Require heart rate data? checkbox in the side panel. This will revert to the previous methodology and the bars depicting other athletes will once again be blue.

HR checkbox

If you use a heart rate strap less than the general Crickles population, the new (pink) methodology will tend to move you further to the right of the distribution. Conversely, if you use a heart rate monitor most of the time you’ll tend to move to the left as the activities of non-monitor wearers are added in.

You can see the numerical impact of the change by looking at your change in Cardiac Stress value on the y-axis.

This does not affect any tabs other than Relative CSS.

When will someone run Sub-2 in London

Firstly, a tragic death in London this weekend, widely covered in the press. It will likely be either hyponatraemia (too much fluid and too little salt) or heat stroke, given his age. Time will tell.

One of the other questions was whether or not someone would run Sub-2. The answer was no. Firstly because it was too hot. And secondly because the data said not. It’s not likely to be before 2030 at the rate it is going. I haven’t plotted a 95% CI, but perhaps with a few more technical and training examples, some competition, and optimal conditions, it may be sooner.

See what you think. I have updated some charts I have with the 2018 finish times. I won’t be reading articles about Sub-2 times in London for a while, but on a track in Italy, maybe…





The other week one of our Crickles members recorded something odd. He was cycling on Zwift (Zwift Fondo Wk1 Wo2), and is a keen cyclist, typically putting in 3-4 sessions per week. It’s ideal for the time-crunched, particularly over winter.

He had been noticing something odd for a while, but he and his doctor had dismissed the symptoms. He would notice that his heart had gone “mad” and that he had to slow down or sometime stop. The symptoms would last for 10 minutes at most. He could then carry on.

In recent months he has been wearing a heart rate chest strap more regularly, but still sporadically, and then this happened:

Slide1There was a sudden jump in his heart rate. Most importantly he felt odd with it too. It came at the end of the ride. The heart rate was out of kilter with his power output. It wasn’t “geometric” – that is there was variability in the heart rate. It fell slightly as his power output fell. Naturally he finished the ride.

For all of these reasons, it looked like a genuine heart rhythm problem. So, he got an AliveCor. This is a small device which pairs with a smartphone or tablet and can record a single lead electrocardiogram. You can buy them from the manufacturer, or Amazon.

A few days later, whilst running, his heart rate jumped again, and this time he caught it on the AliveCor:

Slide2This shows a supraventricular tachycardia, with a heart rate of 220bpm or so. It’s just gone back to normal at the end of the trace. Although you can’t quite see a “QRS” complex (a sign that the bottom part of the heart, the ventricle, has activated), you can see a pause and a “p wave” (a sign that the top part of the heart, the atrium, has activated).

This is a common, not life-threatening, rhythm problem. Most people have a single connection between the atria (at the top) and the ventricles (at the bottom, the pumping chambers of the heart). Some people have two (or more), and then, under certain circumstances, the electrical signals can pass down one of the connections and back up the other, looping round in a small circuit and stimulating the heart to go quickly. This is technically known as an atrio-ventricular (nodal – if the pathways are in a structure called the atrio-ventricular node) re-entrant tachycardia. In this case, it’s most likely that both connections in the node.

The definitive treatment is an electrophysiology study and ablation. This maps out the pathways and burns or freezes one of them. It has a good success rate, and is usually curative (about 90-95%), and a low (but not zero) complication rate.

He is on the list for this procedure (thanks Graham!), and in the meantime is on a drug called flecainide, as he will have to wait a little while. The drug is working. But drugs aren’t ideal when there is a procedure that can cure the situation.

The irony is that it’s my son. I never thought that when we started this project, the work would help me directly.

Good luck to those running the marathon today. I’m out for a ride. With my son. It will be his longest to date at 100K. I’ll be honest to say I am a little nervous.



Michael Goolaerts – Part 2

I am sure many of you will have seen the tragic footage by now. He was dead on the bike. He came around the corner and went straight on into the bank with no effort to protect himself or steer. It was shocking.

There was this statement, widely reproduced:

“The autopsy confirms the previous hypothesis that death was due to a heart attack and not a crash. He suffered an attack while racing. His heart stopped, and that’s why he crashed”

Remy Schwartz, the state prosecutor for Cambrai

The slight issue I have is with the word heart attack. A heart attack is a specific term for when a blood vessel in the heart becomes blocked and part of the heart muscle dies. This can result in death. Heart attacks are possible, but vanishingly rare. He could have dissected a coronary artery – that is where an artery splits. He could have a coronary artery anomaly – that is where an artery takes an unusual course in the body and can get compressed during extreme exertion. Finally he could have typical coronary artery disease, but the chances of someone like him having typical coronary artery disease (which normally takes decades of smoking, diabetes and high cholesterol levels to provoke) must be vanishingly rare.

What is more likely is that they meant heart arrhythmia – that is the heart beating too quickly – ventricular tachycardia or fibrillation. It is common to call a cardiac arrest (where the heart stops pumping blood effectively) a heart attack, and the two are very different. Let’s see what further tests show.

I guess what has shocked me the most is how most coverage focused still on Sagan (who, to be fair, rode amazingly), and how the world moved on to the Amstel Gold race. I don’t think that life will have moved that quickly for his family, friends and team-mates.


Aggregate Monthly Timeline

The Timeline in the Crickles Navigator shows your Cardiac Stress for each activity in the selected Date range. There is now a new feature that enables you to see your aggregate Cardiac Stress month by month. To select this visualisation, when you’re on the Timeline tab check the Aggregate monthly timeline? checkbox in the side panel. Then you’ll see a chart like this:


Each point on the chart now represents a whole month rather than a single activity. Also, the x-axis here doesn’t depend on the Date range but reflects the full extent of your history loaded into Crickles. The first point of every year – the one that sits exactly on the vertical year line (e.g. the first point in the figure, which lies on the 2015 line) corresponds to January and the last point, which sits before the start of the next year, shows the December value.

The points are still coloured by Cardiac Intensity and sized by Hours of moving time, as on the normal Timeline. However, since aggregating by month tends to even out differences, the size scaling is emphasised on the Monthly display.

This new chart gives you the ability to identify your easier and harder months, and to see at a glance how the Cardiac Stress accrued in a particular month arose from duration   versus intensity of exercise. For example, in the figure you can see that after a month of very low Cardiac Stress in October 2016, the two months following saw a return to higher levels, generated by greater intensity – this was due to the increased difficulty of achieving previously normal performance after a period of de-training.

Obviously the last point on the chart will normally reflect the current month so Hours (indicated by size) and also the level of Cardiac Stress will tend to be lower than normal until the month comes to an end. There is no correction for shorter/longer months.

To compare your results with others, use the Compare Groups? checkbox. This brings the Group dropdown into play, giving you the ability to compare your monthly Cardiac Stress to all other Crickles athletes, or to sub-select based on your gender or age:


The larger the group you compare to the more Intensity will tend towards mid orange and the less variability there will be in Hours. You will also notice a seasonal trend with a high in Summer and a low in Winter (so long as the Crickles cohort remains heavily weighted towards the northern hemisphere!).

Michael Goolaerts

I was going to write about something else this weekend. But then I read that Michael Goolaerts had a cardiac arrest at Paris-Roubaix.

He reportedly had a cardiac arrest after a crash and received CPR at the roadside.

We don’t know much more at the time of writing.

He may have simply crashed and struck his chest. He was on the cobbles at the time, and they are notorious. Commotio Cordis is the term given when a blow to the chest wall put the heart into ventricular fibrillation. It’s most common in boys/young men when they are playing sport. It’s more common than you might think. According to Wikipedia there were 188 cases in the US between 1996 and 2007. 4 in 5 died.

There are a few conditions which he might have had. I thought that cycling at this level would require a basic history, exam, electrocardiogram (which looks at the electrical system) and echocardiogram (echo). An echo is not necessary it would seem (see here). Echocardiography looks at the structure of the heart and is a very common test that is requested on most patients a cardiologist would see. If I was competing at such a level (which I never will) I would want one. Therefore the medical exam has to be considered as pretty cursory.

Nonetheless, the screening as it is might be expected to exclude conditions such as hypertrophic cardiomyopathy (the muscle layers of the heart become disorganised), possibly arrhythmogenic right ventricular dysplasia (fat replaces muscle in the heart), and significant valve disease such as aortic stenosis (blood can’t get out of the heart properly). These are structural problems with the heart which can result in sudden death. Problems with the electrical system such as long QT syndrome or Brugada syndrome (these can predispose people to abnormal life threatening heart rhythm problems) could also be picked up.

Aside from an echo, an exercise ECG might help too – that is an ECG recorded during (and shortly after) exercise. One of the most common causes of death during exercise in young people are aberrant coronary arteries. The coronary arteries supply the heart with blood. Sometimes they take odd paths through the body. There is one route which they sometimes take when one of the runs between the aorta (the tube that takes blood from the heart around the body) and the pulmonary artery (the tube that takes blood from the heart to the lungs). At times of physical stress the coronary artery can become compressed and blood can’t get to the heart, resulting in cardiac arrest. You can see the early stages of that on an exercise test.

There is always the spectre of drug use too. I hate to say it, and I hate to think it, but I am still suspicious of what goes on in professional cycling (and other sports).

Sadly the outlook from “out-of-hospital”, and indeed “in-hospital” cardiac arrest is still poor. But I hope he will be ok. He will have been spotted quickly and had good cardiopulmonary resuscitation early, which will improve his chances. He’s also young and fit, which again stands in his favour. Fingers crossed.


Closest in Age

To view results on the Crickles Navigator you are now required to provide your Date of Birth. This enables us to run heart rate analysis based upon age and is needed for some of the features that we plan to introduce.

More immediately, it gives you the ability to compare your Navigator analytics with those of people who are close in age. To do this, simply pick Closest in age from the Group dropdown. This then compares your results to those of the athletes who are are closest in age to you:

Closest in age

The number of athletes who appear in light blue will depend upon the number who have signed up and disclosed their dates of birth at the time (as well, of course, upon the selection algorithm, which may change). The label in the top left of the chart shows the percentage of the Crickles population that are included in the Group selection. This now appears for all Group choices apart from All.

The Closest in age comparison applies to all of the tabs for which the Group choice is generally relevant. At the time of writing this is the first four, viz: Relative CSS, Relative profile, All-in and Summary. For each of these you can now compare your values with those of age-similar peers on Crickles.

For example, on the Summary tab when I select Closest in age I can see that my Current LTHR is at the 81st percent for my age group, whereas it’s only at the 59th percentile for the overall Crickles population (not illustrated here but can be seen by setting Group to All):

Closest in Age Summary

The identity of the athletes who are picked out as close in age is not disclosed on any o the tabs, nor is your identity disclosed to others when you appear as a comparison for them.

Change to the Fit-Fat charts

The Planner introduced a version of the Fit-Fat charts that, rather than looking backwards, projects forward into the future. Since its purpose is to assist with fitness planning, the Planner introduces High Fatigue warning lines to show when a proposed training load would push the athlete to a level of Fatigue that would be high for the athlete and/or high for the entire Crickles cohort.

This presentation of Fitfat charts is now available on Fit-Fat itself. Here’s an example with a Date range from 1/Nov/2017 to 7/Apr/2018:


This works well with short to medium Date ranges. Over a longer Date range the Fatigue, Form and Fitness lines can become unhelpfully overlapping. Also, the High Fatigue lines become somewhat redundant: in the limit, if you sample all of your available data by pushing the start of the Data range back to 1/Jan/2015 you get a very good view of how your current Fatigue compares to its historical levels without the need for the warning lines. Accordingly, for longer Date ranges the Fit-Fat display reverts back to its previous form. The cross-over occurs at around six months. In the example above, we can see this happen if the Date range is nudged one month further back:


Over this time horizon of around six months there’s not much to choose between the two views. The more stripped down format works better as the length of the Date range increases and the new format taken from the Planner works better over shorter horizons at which you lose the long-term picture.