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.