Irregularity report

There is a new Irregularity report that is a successor to the old (and long retired) Regularity report. You will have seen on the Activities tab that a Diagnostic reading is available for most activities for which you recorded your heart rate. This can be especially useful as an early indication that your heart rate strap needs a new battery or is mis-performing or that there is an issue with your sports watch. If you a number of Check_Strap readings, this is likely to be the case.

For most activities that have a Diagnostic reading the value is Regular. You are also likely to occasionally see an activity flagged as either Irregular or Unclear. This relies on a Crickles algorithm that detects a particular kind of behaviour in the heart rate pattern. This is certainly not in any way a medical diagnostic nor does it aim to evaluate a range of potential cardiac irregularities. Nonetheless, analysis from Crickles survey responses show that respondents who report heart rhythm issues are more likely to have more “Irregular” readings in this specific sense than respondents who don’t, and the difference is statistically significant (p-value < 0.05). A large majority of Crickles users will see some Irregular readings but those with heart rhythm issues tend to see more.

The Irregularity report shows you how your “irregularity ratio” – the frequency with which Irregular readings crop up – compares to that for the all people who have responded to the Crickles survey. The report has the following elements:

  1. Box plots in black showing the distribution of irregularity ratios for all survey respondents. Crucially, these are split between those who report a heart rhythm issue (top boxplot) and those who don’t (lower boxplot). If you’re not familiar with box plots there’s a handy guide here. (Note that the boxplot on the report is horizontal whereas the link describes box plots shown vertically – this is purely presentational.)
  2. A diamond and vertical line in purple indicating your all-time Crickles irregularity ratio. The line makes it easy to situate the value relative to the two boxplots.
  3. A label next to the purple diamond giving your relative level based on the this ratio and the underlying statistical model.
  4. A blue diamond and vertical line showing your irregularity ratio over the dates chosen in the data range in the sidebar. This defaults to the past six weeks and can be changed so that you can explore how your ratio irregularity ratio has changed over time.
  5. An explanatory label next to the blue line/diamond – there is no relative level here akin to that for the all-time ratio.

This report is only available to users who have completed the Crickles survey. If you have completed the survey but see only an empty rectangle on this report it’s likely to be due to you having a high ratio of Check_Strap readings, suggesting that you have strap issues that mean your data may be unreliable in this context and is hence screened out of the analysis. If you haven’t taken the survey yet and do so in future be aware that there may be a delay, potentially of some days, between completing the survey and Irregularity appearing in your menu bar.

The box plot for all Crickles users (as opposed to survey respondents) is not shown but looks similar to the No box plot only with many more outliers at the high end.

There are a number of limitations to this analysis, including the fact that we only have a limited window of history for each subject and this may or may not overlap with any history of arrhythmia. Also there is a significant selection bias in our sample: people who are motivated to take the Crickles survey are more likely to have an arrhythmia diagnosis than the population at large. If you have any questions or observations about your data on the report please do drop us a line.

We would like to publish our methodology for open review in a medical journal with full anonymity of respondent data. This would enable any other parties with a research interest in this topic to examine our workings in detail and thus help us to validate and improve the methodology. To date, Strava have instructed us not to do this using a prohibitory right that they assert in their API agreement. We will continue to petition Strava for their permission to publish, probably in conjunction with an academic partner. Unless and until we secure Strava’s permission, this report is all we can offer.

Seasonal Heart Rate report

There is now a new Seasonal HR report that shows the relative amount of time you spent at each heart rate level quarter by quarter. This is a much more detailed version of the Seasonal report. For each quarter you get a mini density chart like this:

The x-axis represents your heart rate in beats per minute (BPM) and the y-axis shows the proportion of time spent over that quarter at that heart rate. Your current estimated lactate threshold heart rate (LTHR) is shown as the vertical dashed green line.

You may find that the charts are easier to read if you use the Autoscale tool in the upper right hand corner:

If you’d like to see how your heart rate distribution varies by sport, you can select or deselect all of the sports that you’ve engaged in using the multi-select Pick your sports: widget in the sidebar:

You can use tooltips to see exact values along each curve:

and you can also focus in particular parts of the curves using the drag/zoom feature, using the Reset Axes tool in the upper right corner too reset the display.

Unlike the Seasonal tab (which shows a maximum of 12 quarters), this report will show you a mini chart for each quarter for which Crickles has your history.

This report is only available to users who have completed the Crickles survey.

Colours on the fitness trend report

The colours on the Fitness Trend report have been changed to increase visibility for athletes with two or three years of activities loaded. For athletes with more years of data, or indeed for those with just one year, the display should be unchanged. Please get in touch if you have any thoughts about how the colours are working for you.

enhancements to fitness trend report

The Fitness Trends report has had a couple of enhancements. First, the colours are now easier to differentiate and the points showing actual fitness values behind the trend lines are more clearly visible. Second, a slider control has been added to the sidebar that enables you to choose the degree of smoothing for the trend lines. At the lowest level of Smoothing the trend lines follow the actual fitness values closely:

At the highest value of Smoothing a macro pattern of Fitness over the course of each year is plotted:

You can experiment with different values of Smoothing according to whether you want a general overall picture of your yearly Fitness trend (high smoothing) or a more detailed comparison of Fitness at each point of the year (low smoothing).

To compare the same day in different years numerically you can toggle the hover control that is represented by the two left-pointing bars icon at the upper right of the chart from its default value of Show closest data on hover to instead Compare data on hover:

When you do this and then hover over points on the chart you can directly compare the Fitness values for the same given day in every year:

The boxes that have a whole number for day_of_year show the actual Fitness value for that day whereas the boxes that have a fractional day_of_year show the corresponding trend value. For example, the screenshot shows that on day 179 in 2020 (blue box) the athlete had Fitness of 100 whereas in 2015 (red box) at the same time of the year the athlete’s Fitness was 81. In both cases the trend values were slightly below the actual values on that date.

COVID-19, the heart and exercise

Aside from the well-recognised effects on the the lungs, COVID-19 infection can affect the heart in a number of ways. Firstly, COVID-19 can make the blood more sticky leading to blood clots. This, combined with oxygen deprivation can cause a heart attack, which is where part of the heart becomes deprived of an adequate blood supply and dies off. However, it would appear that the virus can affect the heart directly, causing heart muscle damage. This can lead to heart rhythm problems and heart failure. When COVID affects the heart in this way, it is termed myocarditis. Damage to the heart at the time of COVID-19 infection is associated with a higher death rate. Many viruses can do this, and this one is no exception. The type of damage that has occurred can be determined by MRI scanning. 

It may be more common than is widely appreciated. COVID-19 infection is still a new infection and we are still at the early stages of understanding it. Although many people appear to have no or few symptoms, it’s clear that some people are severely affected and that some people have symptoms that persist for some time after infection. 

After having had COVID-infection, assuming your symptoms have not been too bad, once recovered it would be wise to wait a week to 10 days before resuming athletic activity. It is then a case of listening carefully to your body and easing back into things. It may take a bit longer before you feel completely back to normal. 

If you have had a more severe infection then you may go on to experience extreme fatigue, breathlessness and fast heart rates which can persist for some time. This “long-Covid” is poorly understood and may point towards more significant damage. In this case, it is probably wise to avoid sporting activity and seek further medical evaluation. We need to emphasise that we are in the very early stages of understanding this disease. Therefore, be aware that the advice may change frequently as more and more is found out.

Fitness trend analysis

There is a new Fitness Trend report on the Navigator that enables you to compare your fitness trajectory from year to year. Here’s what it looks like for someone with data going back to the start of 2015:

Each coloured line represents the fitness trend for a calendar year. The points behind the trend lines show actual unsmoothed Fitness values. For example, the yellow 2020 line on this chart shows that the athlete’s fitness throughout July and August was trending above all prior years except for 2018. Currently (mid September 2020, at the time of writing) the athlete’s trend fitness is at about the same level as in 2016 and 2019 and well above 2017 and 2018.

Zooming and hover tips are also available. Here, we zoom in on the same chart for the period around August and hover over the 2018 point near the start of the month:

Hovering on the trend lines rather than the points will show (non-integer) trend values rather than exact point values for an exact date.

The Irregularity report has been temporarily removed from the Navigator. A new and improved version of this important report will be re-introduced for users who have completed the Crickles survey in due course.

Timeline, lthr and ftp charts are now zoomable

The Navigator’s Timeline, LTHR and FTP tabs have been enhanced to operate similarly to Fit-Fat. By default, analysis for all of your available data is now shown and you can select a region of interest, such as the most recent time window, by dragging a rectangle over the desired area to select it. Double-clicking the chart then resets it to zoom back out and show all data.

If you have several years of data on Crickles and many activities, the Timeline tab in particular can initially look busy as this example shows:

However, it’s easy to select, say, just this year by drag/zooming to simplify the chart. Here’s how that same screen looks with only the 2020 portion selected:

Note also that there are now hover tips on this view showing the name you gave the activity together along with with key values:

The LTHR and FTP tabs also now operate similarly, defaulting to a view of the entire available date range with zoom and hover enabled, as this (unzoomed) example shows:

The lockdown in one chart

Using Crickles data we can get insights into how the lockdown has affected us and answer questions such as:

Did we do less outdoor cycling during the lockdown?
How much more time did we spend on the turbo trainer?
What else did we do more or less of?
Are we reverting to pre-lockdown behaviours yet?
Have changing patterns of exercise behaviour varied between countries?

Here’s a single chart that addresses all of these:

Each column represents a geographical zone – the UK, the EU except the UK, the US, and the rest of the world. Each row depicts an activity – outdoor cycling (Ride), indoor cycling (VirtualRide, including all turbo trainer rides), running and walking; there is also a row for all other activities. Each point shows the average hours over a month for which people in each region engaged in each activity. The blue line shows January to August last year and the pink line shows the same period this year.

Looking at the UK (the first column), we see that the amount of outdoor riding was down on last year in February, March and April but recovered to 2019 levels by May. On the other hand, the amount of indoor cycling has been markedly higher this year since February, especially in the period from April to June. We’re also doing more walking and more of other sports, the most significant of which are workouts and weight training.

The picture is broadly the same elsewhere but there are differences. Europeans were back cycling outdoors at or above 2019 levels by May and were only notably down on their 2019 levels in April. They took to their turbos with equal gusto but got off them a month or so earlier than we did. The majority of their large number of Other hours recorded in January 2020 are unsurprisingly accounted for by skiing,

Europeans – at least those on Crickles – do more running than Brits and increased their 2020 levels relative to 2019 in May and June. Our US cohort does even more running than the Europeans, and less cycling. Their indoor cycling levels were already higher than in 2019 from the start of the year – perhaps because Zwift and other indoor platforms have been well marketed in the US, where more extreme winter weather in much of the nation may be expected to generate a receptive home market. Other than that, the most marked change from last year in the US is an increase in walking and hiking in the Spring.

In the rest of the world the most conspicuous change this year has been a dramatic switch from outdoor to indoor cycling in April and May, with the momentum on indoor platforms persisting beyond that.

Overall, the chart seems to show that, at least for now, most people have reverted more or less fully to their former exercise behaviour, perhaps with more walking.

Seasonal report can now be analysed by Sport

The Seasonal tab enables you to see how much time you spend in each heart rate zone by Year/Quarter. The heart rate zones are estimated adaptively and change in line with your prevailing fitness. This report has been in place for a long time. What is new is that you can now break it down by Sport.

Sport defaults to TOTAL, and so long as this is selected the report is unchanged from how it has always been:

However you now pick a single sport from all of those that you have recorded on Strava for which you have heart rate data:

This will then show you the time that you’ve spent in each heart rate zone for that Sport. You may see that there are fewer Quarters showing if you only occasional engage in that sport or if you often don’t use a heart rate monitor for it.

This new feature gives you the ability to see the differences in the nature of your training effort across different sports. For example, you can isolate and compare Rides or Runs and ensure that the amount of Zone 1 time shown on the charts doesn’t include any time you spent doing Yoga or Walking.

(Note that this tab also still has controls to select a Date range and a Group but these have no effect on this report.)

CSS Factors

This is a new page in the Navigator that gives you a comparison of how your cumulative Cardiac Stress Score compares to that of your peers on Crickles. By default, the period over which the sum is taken is the last six weeks and your “peers” are those who are closest in age – both the period and the comparison group can be changed in the sidebar.

Here’s what it looks like:

The uppermost bar, labelled Total_CSS, shows where your summed Cardiac Stress Score ranks relative to peers. The midline represents the median value; values to the right are relatively higher and to the left are relatively lower. If you hover over one of the bars you can see your value alongside the highest and the lowest from your peers:

In this example, the athlete’s CSS is amongst the higher ones. The hover tip shows that at 4,217 it’s well above the median of 2,305 although far lower than the highest value of 7,715. You can see the exact distribution of the CSS values for all athletes in the peer group by looking at the Relative CSS tab. You can see which of your activities contribute most of the CSS from the Activities tab and the Timeline tab. If you do more than one type of sport, you can get a breakdown of the CSS total as well as insight into the hourly cardiac stress rate on the CSS by Sport tab.

The other three bars on the chart above show the relative levels of the factors that go to make up CSS, which are:

  1. The weighted average cardiac intensity for your activities over this period
  2. The number of activities that you’ve logged in the period
  3. The average duration of those activities.

In this example, you can see from the chart that the athlete has done many more activities than most peers, although the activities are, on average, shorter. The exercise intensity is just a shade higher than the peer average. In all cases, the hover tips show the relevant values, so, for example, the athlete’s average activity duration is 1.3 hours, which is below the median value of 1.5 hours and well below the maximum average value of just under 4 hours. (Duration actually captures moving time, not elapsed time.)

Lower values are coloured to be progressively more blue and higher values are progressively more red.

As with much of the analysis on Crickles, the purpose of this tab is to enable you to understand how your exercise load compares to that of other keen endurance athletes. In the absence of established levels for how much exercise might be “too much”, you can at least see whether you’re doing more or less than other people of a similar age, using a methodology that is consistent across different sports.