New Summary tab for the Navigator

The Crickles Navigator has a new Summary tab giving headline figures for the athlete and a comparison of each with peers. Currently, there are six figures shown in the Value column:

Period CSS shows the total Cardiac Stress Score for the period defined by the Date range. This period defaults to the last six weeks but can easily be changed in the side panel.

Period XSS extends this measure to cover also activities on Strava for which there is no heart rate data. The estimate of cardiac stress is less good than CSS, which  requires a heart rate monitor, but better than assuming that it’s zero. If you always wear a heart rate monitor CSS and XSS will be equal (though not for the peer group). If you never wear a heart rate monitor, CSS will always be zero but XSS will usually be positive.

Current LTHR is the latest Crickles estimate of your Lactate Threshold Heart Rate. (Occasionally this estimate may lag one activity behind your last effort.) This only appears if you use a heart rate monitor.

Current Fitness, Fatigue and Form are as described here. Since they are current estimate, neither these values nor Current LTHR change as you change the Date Range.

The numbers alongside these in the Crickles Percentile column show how you compare to the Group chosen in the side panel (by default, the entire Crickles population). If the Crickles Percentile is 100 you have the highest value. If the Crickles Percentile is 50 you’re on the median.

By design, this tab works particularly well on the iPhone.


Over time, we may add more information to this tab.

NB: There is a known bug that the Summary tab will be totally blank (i.e. no data) if you have included the character “(” in your Strava name. If this affects you and you’re interested in seeing your Summary data before I otherwise get round to fixing it, please let me know!


Improved layout for the Timeline

The Timeline (previously called CSS (Cardiac Stress Score) Map) on the Crickles Navigator has been overhauled to display data differently. Now, the x-axis is the timeline, which still reflects the Date Range on the side panel, and the y-axis shows the CSS for each activity. This makes it easy to pick out which activities have the highest CSS (those that lie highest on the chart) and when you did them (more recent to the right, least recent to the left). The composition of CSS into its elements is now encoded through size, which represents moving time – larger dots are longer activities – and colour – the least intense activities are green and the most intense are red.

Here’s an illustration – note that CSS Map now appears as Timeline as the tab name:


In this example, the activity with the highest CSS occurs half way along the chart at the top. The size (large) and colour (medium orange) indicates that the activity was long in duration but only moderately intense.

You will also see that there are some grey dots. This is because the Timeline now also includes activities for which there is no heart rate data and so Cardiac Stress has to be estimated from moving time alone.

Changes to the Navigator

There are a few improvements to the Crickles Navigator:
Athlete selection
It now remembers who you are (i.e. which athlete you selected) between sessions. This is achieved using a cookie (it simply stores the athlete ID); the first time you load the Navigator following this change there is a notification that pops up alerting you to the use of cookies. The cookie will periodically expire but in the main you’ll now no longer have to find your own name in the Athlete list.
The same has been done on Crickles Charts too.
Group selection
Group selection is now under Athlete selection so that you only have to select from the groups to which you belong. For the majority of athletes, this reduces to a choice between “All” athletes (the default) and Male or Female.
Lactate Threshold Heart Rate (LTHR) and Functional Threshold Power (FTP) are now charted on separate tabs. This makes changes in LTHR in particular easier to discern. Obviously if you don’t cycle with a power meter you won’t get an FTP chart.
Last loaded date/time
The notice of when Navigator data was last updated was previously given in the arcane UTC timezone beloved of computers. This is now changed to London time.
Please let us know if you have issues with any of the above.

Running a Marathon – Will I die?

There is no doubt there is a big difference between myself and Ian. He will be going off to Italy to cycle up a hill in October on a very nice bike. It will be sunny and there will be wine and olives. Later in the month, I am off to run a marathon in Dublin. I won’t bother checking the weather. It will be cold and wet. And there will be no wine at all, although hopefully some Guinness, so not all bad. There are times when I wish I had put a bit more effort into maths at school.

I do worry about running “long” distances, and what strain it puts upon the heart. But what are the risks of dying during a marathon? You can’t rely on newspaper headlines. They only report the bad events. They don’t write headlines along the lines of “Marathon run today, nobody died”. It’s therefore important to look at studies where it has been planned to study the outcomes, or where outcomes are tracked over a long period. But finding raw data is harder than you might think.

I thought I would start with the Berlin marathon. It’s on soon – typically taking place at the end of September. And it’s fast – a place to set world records. More importantly it’s run by a lot of people – 46,950 people in 2016. When there are big numbers there can be good data. Unfortunately, after emailing them, they don’t keep statistics. So that’s no good.

What about London? In 2001, I “ran” the marathon. It turns out that not running at all in the previous month because of a knee injury and drinking wine each night doesn’t make for a good marathon. Being overtaken by a tree is pretty galling.

The first London marathon was staged in 1981, and since then over 1,000,000 people have completed the race. There have (probably) been 14 deaths since then, although it depends on how things are counted, and there are discrepancies between reports.

From 2007, race statistics and details of deaths are pretty secure. David Rogers, aged 22, died that year from hyponatraemia (water intoxication). In 2011 Claire Squires, aged 30, died of heart failure in front of Buckingham palace. It was felt that DMAA, a now banned amphetamine stimulant, contributed (it wasn’t banned at the time). In 2014 Robert Berry, aged 42, died from heat stroke. In 2016 David Seath died from heat stroke (probably) aged 30.

258,911 men have completed the race since 2007 (including 2007 and 2017) and 140,271 women. So, the death rates are 1.2/100,000 for men and 0.71/100,000 for women.

If you accept that 14 have died over the course of the race, and that 1,039,225 people have completed it (a combination of race reports from the London Marathon website,, and a page on peakendurance then the overall risk rises to 1.5/100,000 for both sexes.

Boston is another famous city with a famous marathon, unfortunately for sad reasons at present. I’ll be looking out for Stronger when it is released in the UK. There is a professor at Harvard who has collated some data. When it arrives in the post, I will update the blog with the key points.

The New York Marathon is the world’s largest. It started in 1970. They have a great analytics page ( Tata Steel aren’t popular in the UK, but Tata Consultancy Services are my new friend. 1,070,784 people have participated in the NY Marathon since 1970 – 764,609 men and 306,175 women. The average man aged 40-49 completes the distance in 04:15:57. Finding the deaths is a little harder. 3 died in 2008. They don’t keep those stats on the website, and more data trawling is required. I have emailed them, but won’t hold my breath.

What have I learned? Finding out accurate data is hard. I still have more stones to look under. And marathon organisers don’t want to hear about deaths or advertise them (odd that…). If you have access to any data please let me know. But one thing is certain: deaths running a marathon are mercifully rare. It’s about the same risk as spending an hour on a plane (

I’ll book a return ticket back from Dublin. The flight is quite short.


“All-in” analysis on the Navigator

CSS is a great measure of Cardiac Stress and, quite naturally, it relies on the athlete wearing a heart rate monitor (HRM) during exercise. However, sometimes we exercise without a HRM and sometimes we want this to “count” towards our overall accrued CSS. This is recognised in the Fit-Fat tab, which makes an estimate of CSS even for activities in which a HRM is not used.

This same estimation methodology has been extended to give an estimate of CSS its components; this is shown on a new All-in tab. Here, you can see four charts:

First, an estimate of CSS that takes into account all activities recorded on Strava, even those where an HRM was not used:


Here, the purple mass (technically, a density plot) shows the distribution of estimates amongst all Crickles athletes over the chosen period. We can see in this example that the most common value is at about 2,500, there are quite a few athletes (around 1/5th of the number at 2,500) at 5,000 and even a blip indicating one athlete over 20,000.

The vertical black line picks out the value for the chosen athlete (me in this example), and you can see that in this case the athlete (me) is bang on the most common value.

If an athlete wears an HRM all the time the estimate of CSS will be as good as we can get. Conversely, to the extent that an HRM is not used the quality of the estimate will decline. The second chart shows this quality for the given athlete over the chosen period:


Again, the purple mass is a density plot showing where Crickles athletes overall lie on the quality chart. Happily, the most common value is at over 90%. About 1/6th of the number at this high value are at zero, indicating that they didn’t use an HRM at all over this period. Again, the vertical black line represents the chosen athlete and again it’s me. I’m at about 87.5% usage. To verify consistency, you can multiply this percentage (87.5%) by the CSS estimate (2,500) we just saw and that will show the CSS that you see on the Relative CSS tab (about 2,188).

Very thoughtful readers may correctly spot that when you’re on a bike with a power meter Crickles is able to give a high quality estimate of CSS even in the absence of a HRM. This is indeed true but this is not reflected on this quality chart.

The third and fourth charts show the components of the full CSS estimate. These are Intensity:


and average weekly exercise hours:


The Intensity estimate is subject to the same estimate quality as the full CSS estimate (more HRM usage -> a better estimate) whereas the weekly exercise hours are a simple sum of “moving times” and are unaffected by HRM (non-)usage.

These charts work the same way as the others: for example, the most common weekly exercise time amongst Crickles users over this period is shown by the last chart to be five hours (the peak of the purple mass) and I did fractionally more than that (the vertical black line).

Death During Exertion

“Enduroman Events‏ ‪@EnduromanEvents Aug 7

We’ve put lights on #DougWaymark at 2000 on last feed. Sun is setting. Calais is lit up as we head down with the tide. Wind has dropped.

Enduroman Events‏ ‪@EnduromanEvents Aug 7

2030 water taken. Moon is rising behind a cloud over Calais. Air temp dropping, light fading. ‪#DougWaymark swims on. ‪#Arch2Arc

Enduroman Events‏ ‪@EnduromanEvents Aug 8

Our friend Douglas Waymark sadly passed away during his Solo Arch to Arc. Enduroman community miss him. Short tribute ‪”


It’s impossible not to be moved by this series of tweets.

Many of you will have read of the sad death of Doug Waymark this week, as he attempted to complete the Arch to Arc challenge. This is a run from Marble Arch in London to Dover (87 miles) followed by a swim across the channel (21 miles) followed by a cycle to Paris (180 miles). Only 25 people have completed it. The record is 59 hours and 56 minutes.

Doug got into trouble during the swim, 12 miles off the coast of Dover. He could not be resuscitated. He was an able athlete who had completed ultra-events before. It’s impossible to know at this stage exactly what happened.

Phidippides is said to have run from Marathon to Athens to deliver news of a military victory at the Battle of Marathon. On delivering the news he died suddenly. Death during exertion is mercifully rare, but always shocking. How can it be that someone who is fit and well can die so suddenly?

The most common cause of death during exercise in men over 40 is coronary artery disease – a blockage of one of the coronary arteries. These arteries supply your heart with blood. When one blocks, an area of the heart can’t function any more. If it is a branch of a small artery you may not notice. If it is one of the larger arteries you will typically die very rapidly. What people don’t understand is that an artery can go from open to blocked very quickly. And therefore, you can have no symptoms at the start of a race. As you get older you build up deposits of fat, covered over with a thin layer, in the arteries. This thin covering can rupture and then a clot can rapidly form, blocking the artery. Furthermore, because the human body is amazing, it is possible for the body to compensate for quite significant problems in the coronary arteries before symptoms arise.

An alternative (there are many) is that he could have torn one of the coronary arteries – coronary artery dissection – or the aorta itself. This can happen under periods of intense strain, although it is less common. Some people have coronary arteries that arise from slightly different locations (anomalous coronary arteries) and these seem to be the cause of sudden death during exercise in some people.

In younger people, hypertrophic cardiomyopathy seems to be the most common underlying condition which causes sudden death during exercise. This is a disorder of the heart muscle. Normally the heart muscles are laid down in neat sheets – the muscle cells are aligned. In hypertrophic cardiomyopathy (HCM) the muscle cells look like they have been scattered and the term used is disarray. People suffering from HCM are more prone to heart failure and heart rhythm problems.

There are other possibilities too – such as problems with the right ventricle (arrhythmogenic right ventricular cardiomyopathy) and problems with the electrical systems (Long QT syndrome, catecholaminergic polymorphic ventricular tachycardia – they all have obscure names). More on these in future articles.

But the reality is that death during sport is rare. About 1 in 1,000,000 young people die during exercise each year and about 6 per 100,000 middle aged people. And that is why Doug Waymark made the news.

More lives are saved by exercising than caused by it. But as with all things in life, nothing is completely safe. Reading the news suggests that Doug was someone who helped and inspired others to achieve their goals. He will have saved many lives, although tragically lost his own.










Coronary Artery Disease

On Tuesday night, I ran 10K. It took just under an hour. My heart rate went no higher than about 130bpm. I stepped off the treadmill, had a quick shower and carried on with the day. I didn’t have any pain. It felt good.

Perhaps this shouldn’t be a cause for celebration. It’s not an exceptional time and I am firmly middle of the pack at my local Park Run on Saturdays. But it was for me. 16 years ago, I stopped running. A year ago, or so I started again on holiday. It was awful and I could barely run a mile with the kids.

Since then there has been a battle with iliotibial band syndrome, Achilles tendonitis, shin splints and a slipped disc. I have had physio and after several insoles, I am now on my third pair of shoes (Mizuno Running Solution selected – it worked!). I am best friends with a foam roller. I am also 20Kg lighter.

I am now edging towards 50K a week. Most of it is pretty low intensity and in Zone 2/Zone 3. But, what also went through my mind in what was a pretty boring hour on the treadmill was the nagging question as to whether what I was doing was healthy and good for me.

Coronary heart disease – the narrowing of the coronary arteries which supply the heart muscle – is bad. When the narrowings reach a certain point, then on exercise not enough blood can get to parts of the heart. This typically (but not always, nothing is ever always in medicine – some people get breathlessness or undue fatigue) causes pains in the chest. The pains are usually described as an ache or pressure – angina. If an artery blocks suddenly then part of the heart muscle can die – a heart attack (myocardial infarction). This is usually painful – people get severe and prolonged pain, they are often pale and sweaty. They can feel nauseated and vomit.

Coronary heart disease is more common as you get older, if you are a man, or if you have high blood pressure, diabetes or a high cholesterol. It runs in families too. If you want to get an idea of your risk then follow this link:

A marker of coronary artery disease and risk is coronary calcium. This gets deposited with age, along with cholesterol. You can see it on CT scans particularly clearly. Typically, if you take a group of ordinary individuals, the more calcium that is there, the more likely you are to have a heart attack.

Athletes have more calcium in their coronary arteries than non-athletes. And coronary artery disease is the most common cause of sudden death in athletes. I can recall a couple of people on the ward recently who “died” and were then resuscitated during exercise. It’s not uncommon.




So, exercise is bad then?

Not so fast. In fact, generally, the more exercise you do, the less likely you are to have a heart attack. Some articles suggest your risk is about 50% less (but NOT zero). This is one of those annoying paradoxes that crops up in medicine all the time. It is probably down to the composition of the plaques that are seen – the plaques in athletes are more “stable” – less likely to rupture and cause a heart attack. More work is required to understand this though.

So, keep exercising – but listen to your body. If you are doing the same route and you are struggling more than you would expect then be careful, although everyone has good and bad days, and everyone ages. If you are getting chest tightness when you exert yourself which eases off with rest, then seek medical attention.

Post Script: I ran 24K on Saturday. It felt good. But, of course, the jump was too much and now my knee is sore and swollen. I really should know better…

The Basics…

So, I’m intending that this blog should be a basic course in the heart and how it adapts to exercise. It’s fair to say that this is something of a complex topic, and there is much controversy and debate. We have not got it all worked out by a long way, and I reserve the right to completely change my mind about things over time. That is the nature of medicine.


The heart is only one part of the cardiovascular system which helps you exercise. It includes the heart, the lungs, the blood, the muscles and of course the brain. My PhD touched on how the nerves and brain react to exercise. It was 3 years of pure frustration, as it turned out to be quite hard.

The first thing to understand are some basics of the heart itself. You can skip this if you already know all about it, but I will assume some sort of basic knowledge in future posts. You will have covered this in GCSE biology, or for those of us who are old and decrepit enough, O level biology.

Have a look at this picture.

Blood comes back from the body having been “used” into the right atrium via the superior vena cava (from the arms, chest and head) and the inferior vena cava (from the rest of the body). It’s important to realise that there is vast variation in the precise distribution. The right atrium is a thin walled chamber which discharges its blood into the right ventricle via the tricuspid valve. Valves are thin-walled structures that are elegantly complex pieces of engineering that keep blood going in one direction through the heart. People write entire books on valve structure and function. Valve disease can be important when considering exercise. 1-2% of the population have a “bicuspid” aortic valve, and exercise can accelerate it narrowing – it then usually requires replacement which is a major operation.

The right ventricle is the pumping chamber that forces blood into the lungs. The system is at low pressure, and the muscles of the right ventricle aren’t as well developed as those on the left side of the heart – the right ventricle is a bit thinner, and probably a bit more vulnerable to stress. This is thought to be important in the development of conditions such as ARVC (arrhythmogenic right ventricular cardiomyopathy) – more on this later. Blood flows out of the right ventricle and into the pulmonary arteries and the lungs themselves.

Once all the business of gas exchange has been done in the lungs (oxygen in, carbon dioxide out) then the blood comes back via the pulmonary veins into the left atrium. During most of my training the pulmonary veins were possibly one of the least exciting anatomical structures you had to learn about, but then it was discovered that AF starts there quite often, and now many people spend entire lives studying them.

The left ventricle is considered to be the main structure of the heart. Blood enters this from the left atrium via the mitral valve. It leaves the left ventricle via the aortic valve and passes into the aorta and from there around the body. Cardiology has traditionally focused on the left ventricle and its function.

One of the key concepts when understanding how the left ventricle works is the “ejection fraction”. This is the proportion of blood ejected from the ventricle each time it beats. Cardiologists, and patients, get very hung up on this measure, and it is important, but there are important limitations. The normal volume of the left ventricle is about 140ml in a typically sized person. Typically, around 2/3rds of the blood is ejected each time the heart beats (about 90ml). Anything over 55% or so is considered normal. But really, what the body needs is not for the left ventricle to have a particular ejection fraction, what the body needs is enough oxygen delivered to the tissues. That depends on how much blood is pumped around the system each minute and how much oxygen it is carrying. Doctors often forget this. I’ll talk more about this in another post. Disease of the heart muscle is termed cardiomyopathy. When people talk about “heart failure” they are usually referring to disease affecting the muscle of the left ventricle. Exercise, particularly endurance exercise can affect the heart muscle in both good and bad ways.

The aorta branches many times when passing blood around the body. The first are the coronary arteries. In most people, there is a right coronary artery and a left coronary artery – the first part of the left coronary artery (the left main stem) branches early into the left anterior descending artery and the circumflex. Narrowings in these arteries cause angina – a pressure or discomfort on exertion (usually) felt across the chest. A sudden blockage can cause a heart attack. There is a lot of debate about whether or not exercise causes changes in the arteries, and whether or not those changes are harmful. Again, a subject for a future post.


So that is the whirlwind tour of the heart structure. In future posts I will touch on valve disease, diseases of the heart muscle and coronary artery disease. Then having finished with the plumbing I will move onto the electrics. It will become clear that in fact as doctors we probably know less than you think. The world of sports medicine is in its infancy really.




Seasonal time in Zones

The Seasonal tab has now been re-introduced to the Navigator. Now it shows you your time in each heart rate zone for each of the last eight Quarters (subject to your Strava history going back that far). This enables you to see whether you really were base building over the winter and adding intensity in the early season – or doing whatever your training plan called for. It also makes it easy to compare your quarter-by-quarter efforts with those from a year ago.


The definition of the zones (Z1 to Z5c) are essentially the same as those defined by Joe Friel in articles that can be found online. The main difference from those and similar methodologies is that the Crickles estimate of your Lactate Threshold Heart Rate (LTHR) is calculated adaptively from your Strava data and applied consistently.

You’ll also notice that we have reverted to a light colour scheme for the Navigator and Crickles Charts. The Activities table on the Navigator works much better this way, and sometimes it’s just good to have a change.

3 quick ways to use Crickles

If you’re new to Crickles you can begin by using it for these three quick checks:

Check 1: Gauge your cardiac stress

On the landing page [Relative CSS] of the Navigator select your name in the Athlete: dropdown to get a screen like this:


The green bar shows you (me in this example) and where you rank amongst Crickles athletes for accrued cardiac stress over the past six weeks. This is based on activities you’ve entered on Strava with a heart rate monitor. If you’re way over on the right hand side you should be aware that you’re taking on a higher cardiac load than most other Crickles athletes. If you’re towards the left hand side you’re taking on less than the others (assuming that you regularly use a HR monitor and upload your activities).

Personally, I aim to be about where I am here: towards the right but not bang up at the end.

Check 2: Gauge your event readiness

If you have a race or special event coming up in the next few days, go to the Fit-Fat tab on the Navigator to see a page that looks like this:


Focus on the black graph: this shows Form. If you’ve been holding at or above about 10 for a few days and you’re now hitting 20-25 you’ll be in great shape for your event. If you’re in negative numbers you’re under-recovered. It’s normal to have negative Form numbers during training but tapering prior to an event enables the Fatigue (the red line) to fall away while Fitness (the green line) can remain high. Form is the difference between the two.

Obviously, if you’ve haven’t been doing any training a taper period won’t help!

Check 3: Compare a specific activity with a friend

If you have someone you exercise with who is also on Crickles, whenever you do the same activity together you can compare your efforts using Crickles Activity Charts.

Again, select yourself from the Athlete dropdown then select the Activity that you did with your training partner. Next, check the Compare another? box and choose your training partner and their record of the same activity. At this point the Metric dropdown will be populated with the set of metrics that you both have available.

chartsIn this example, Sean and I both used HR monitors and power meters so I could select altitude, cadence, kmh, heartrate or watts. Here, I’ve selected heart rate.

You may prefer to choose Distance rather than Time for the x-axis if you didn’t go round together. Here, I’ve checked the Smooth? box too to give a clearer picture.

This enables you to see where you and your partner were putting in relatively more/less effort. (In the example shown, I started off harder then my ride partner, Sean, put in a big effort on the hills in the middle of the ride while I took advantage of a pace car.)


If you’d like more info on any of these topics or if you have any questions or difficulties, please get in touch through the Contact page.