From the Coaches: Signs and Symptoms of Fatigue

With the final 2 stages of this year’s Tour of Sufferlandria fast approaching it’s the perfect time to dive into the physiological and psychological components of fatigue, and what to expect.

Fatigue: extreme tiredness resulting from mental or physical exertion or illness.1

While generally viewed in a physiological sense, especially around those who workout/train frequently, the impacts and causes of fatigue are not limited to the body.

One of the modern models of fatigue is referred to as the Psychobiological model. The general idea is that the limits of endurance performance are not rooted in physiological barriers, but mental ones. Going into a workout with excess mental fatigue reduces your physiological performance(2 3). If you’ve ever struggled with a workout after a long and stressful day of work, but were otherwise off your feet and properly fueled you have experienced this phenomenon.

For many people training every day is not practical due to time constraints. Completing the ToS not only means riding every day, but forgoing tasks you normally can’t skip. Without even looking at the physiological demands of the ToS, we can see that for most people the time commitment alone will add stress to your week.

Excess stress can negatively impact your quality of sleep(4 5), and many have carved out 30-60 minutes of sleep to accommodate every stage. Sleep is your number one recovery tool. Outside of events, it’s usually better to get an extra 30 minutes of sleep instead of an extra 30 minutes of riding.

Now that we have clarified that you’re probably sleep-deprived and carrying more stress than normal, let’s dig into the physiological side of things.

For those tracking heart rate, you might be surprised to see a lower heart rate for a given power later in the ToS compared to the start or during the weeks leading up to it.

I’ll keep this brief (you can read the long version here).

Your body is controlled by two branches of the Autonomic Nervous System: Sympathetic and Parasympathetic, SNS and PNS respectively. When your body encounters more stress than it’s accustomed to your SNS and PNS respond. For the heart, this chronic stress response causes your heart to respond slower to changes (it’s slower to increase during an effort and slower to decrease during recovery) and reduces how fast your heart can beat at max effort(6).

Even without a heart rate monitor, you can track your heart rate response to fatigue. You’ll get the most useful information out of RHR by taking your measurement in the same position at roughly the same time of day, ideally first thing in the morning before even getting out of bed. All you need is a 15-second timer and the ability to lay in bed for an extra 30 seconds after waking up. Your resting heart rate is a great sign of aerobic fitness and an indicator of fatigue. As your fitness improves your RHR will decrease. During periods of extra fatigue, you’ll notice your RHR is higher than normal.

Many of you have heard about Heart Rate Variability (HRV) and it’s used to detect signs of fatigue. HRV has been measured in medical conditions for well over 20 years(7), but it’s only very recently that it’s been used in healthy individuals to predict physiological performance(8).

While you look at your heart rate as straightforward beats-per-minute, HRV requires the precise measurement of every heartbeat and how the gap-between individual beats vary. That’s why HRV is measured in milliseconds. That value represents the range of time differences between heartbeats. This variation has been directly linked to the activity levels of the PNS and SNS. High HRV indicates increased PNS activity (which tends to mean lower levels of stress) while a low HRV indicates increased SNS activity.

While there are several commercially available devices on the market now, the accuracy of those devices must be taken into consideration. Most use light sensors to detect heart-rate, and therefore HRV, however slight changes in position can significantly change those readings, only direct measurements via ECG have been proven reliably accurate(9 10). Many of these devices will also automatically take an HRV measurement for you, which can lead to its own set of issues when considering how your circadian rhythm among other systems, (wake/sleep cycle) impacts your heart rate (11). This is why HRV should be measured at the same time each day under the same conditions, just like RHR.

I’m not saying you should stop measuring your HRV, simply that you need to look for YOUR unique response in HRV. We all look different on the outside, so it’s not surprising we all function slightly differently on the inside(12). Understanding your response comes down to noticing, recording, and looking back at all the data you have available to monitor fatigue.

I have probably lost many of you at this point, the question of “well how is this article helpful for the last two stages of the ToS!?). If you have never hit high levels of chronic fatigue before, or have never paid much attention to what happens when you do, this won’t help you. BUT this becomes the perfect time to notice and record how you are feeling for the very fact that you SHOULD be hitting higher levels of fatigue in the final two stages.

Here are some questions to ask yourself and bits of information to record.
What’s your RHR / HRV when waking?
What was your peak heart rate today, and how did your heart rate compare to your power output?
How did you “feel” today?
What was your mood this morning when you woke up? Chipper, sad, dreadful, excited?
What’s your mood as you are putting your kit on before the final stages?
How did you feel DURING the stage?
How is your appetite, is it suppressed? Is it out of control and you are worried you might bite the fingers off of a loved one if they reach in for a serving at dinner?
Do you feel hotter than normal? Feel like you are running a low-grade fever(but you aren’t because you checked?
Has it been increasingly difficult to fall asleep at night despite feeling physically drained?

Now is the perfect time to record the answers to all, some, or even one of these questions. And just as importantly, the next two weeks are the perfect time to continue to record your answers to the same question. You’ll get a fantastic look at how you as an individual respond to fatigue. While you can monitor this stuff for the rest of your life, you certainly don’t have to!

HOWEVER, you have already put in tons of hard work getting to this point of the Tour. You can make that hard work even more valuable by squeezing every bit of info you can out of how your body reacts to fatigue, and how it “bounces” back.

You’ll notice that the Post -ToS training plans don’t have traditional Levels, but are “fatigue” based. Chances are you’ll “know” how fatigued you are come Sunday, even if you don’t have the power/heart-rate/RPE values anywhere to reference.

I know all of that sounds like a lot to try and track. You might have a spare notebook laying around or you might already be tracking all of this in various apps. If you’d like a simplified way to record all of this information we’ve created a Google Form that covers all of the above questions.

If you’re willing to fill this form out (most days) for the next 18 days we’ll send you an organized Google Sheet with all of your information so you can continue to track everything on your own. We won’t be sharing any of this information outside of the Sports Science department, and won’t use it for anything other than trying to help improve the SUF app and your training experience with it. Technically we can’t even link your SUF account with this information if you use a different email for your SUF account.

Our (especially my) passion is helping people get fitter and healthier. Tracking your response to fatigue will help you make better training decisions in the future. And if you’re willing to share some of that information with us, we can automate more of those decisions for you, so you can go back to focusing on riding!


-Your likely sleep deprived and extra stressed, causing increased mental fatigue and therefore reduced physiological performance.

-You’re likely to see changes in Heart Rate when you become fatigued.

-Resting Heart Rate, Peak Heart during Exercise, and Heart Rate Variability can all give you useful quantitative measures to track fatigue, but you must look at your metrics relative to yourself/past measurements.

-Since you are likely at above-average levels of fatigue at the end of the ToS, now is the perfect time to track how fatigue impacts you.

-You‘ll benefit in the future from tracking how you feel now, and if you are willing to share that information with us we’ll be able to do a better job of helping you and others in the future.

With all that in mind, go smash these last two stages!


Hi Sir Mac,
Great post as always.
Have you ever heard of this study A pilot study on quantification of training load: The use of HRV in training practice
What can we expect from a “Training Load HRV” ?

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That’s a great post, Sir Mac. Very important to understand the signs of fatigue and learn to both cope with it for pushing yourself further but not injure yourself.

I will complete the google form and tracking my recovery post tour as i do with the recovery and strain, during. It will only help me better understand my body and mind for endurance events and that will help better planning and recovery strategies.

Looking forward to read how others are experiencing fatigue and recovery.

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Great, filled out the form. If my e mail is the same as the SUF app can you link the Google form ? @Coach.Mac.C


Thank for that Sir Mac.

Really helpful and informative.

As a noob to ToS, the only times I’ve been this fatigued is during an event. So I’ve not really had the awareness to worry about how I’m feeling, only to take the next step!

And I’ll get right onto that form, does it help you guys, if the email is the same? i.e. Happy for you to cross ref my data.

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Thanks for the information Sir Mac, it is great to get a detailed insight about this!

Just completed the form and will try and remeber to do it over the next couple of weeks

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Thanks Coach Mac. As much as I want to train and get faster, my body doesn’t seem to recover as fast as most of my Strava friends. I’ve been enjoying monitoring my recovery more often and using that information to guide my training, tho it’s meant some significant deviation from the Suf training plans.

While I’ve gotten better at monitoring my fatigue, I’d enjoy if you write a follow up on how to use that information (changes in RHR, HRV, etc) to guide training decisions (continue with planned workout, easy day, rest day, etc). Thanks again, love the write ups.


Very interesting read thanks.
I only started tracking my HRV 2 weeks ago. This weeks Tour has shown interesting readings.
Wednesday the 17th was my lowest day for readiness and HRV score, being on the sympathetic side, not helped by stress at work on the Tuesday. It then picked up for me Thursday as though my body has absorbed the load.
I found similar 10 years ago on John O’Groats to Lands End cycle event. Although I didn’t have the numbers to show but the body starts to get used to things.

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One interesting sign of overtraining (or extreme fatigue after hard training blocks, at least) I’ve observed in myself is having difficulty swallowing. I seem to have this problem more with drier foods, so maybe it has something to do with dehydration as well?

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This is a really great post, thank you.
I started tracking my hrv (plus rigorously recorded hr and bp) about a month ago, with the expressed goal of trying to get a better handle on fatigue and in particular to try and prevent overtraining.

Thus far I am not getting much from it, but I intend to persevere and see what I get out of it. Even though tss has its foiibles when it comes to HIIT I still find the form measure in TP to be an excellent guide. Looking historically I have an idea of a range for Form that I seem to respond well to and a level below which I’ve traditionally thrown in the towel in sessions. So far, managing my exertion around this has been successful.

Keep it up Coach Mac and thanks again. I’ll be filling the google form in.


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This was super interesting, thanks for all the detail – I absolutely noticed my heart rate being lower during the hard efforts than earlier in the week.

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Mine is inability to stay asleep even when very tired. This is the first thing, and it happens before power starts to drop off


I’ve found exactly that this week too. Combined with having almost no appetite after the ride which is bad when I need to eat to recover for tomorrow!


From my experience that is a pretty normal part of the autonomic stress response from high intensity. Using recovery shakes can really help there as it’s cool and goes down easy.

Any number of brands work and you can also just throw stuff in anf make your own

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Great and timely post. I’ve been tracking my RHR for years and the last 3 days my RHR has been climbing. I’m up from 49 to 53. Not huge but definitely a sign I’m getting fatigued. Only one more stage!

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Sir Mac. Very happy to do this. How do you want me to report on Hrv? I am using hrv4training and I normally just look at the recovery points but, from I can see, also gives me rMSSD?


Cheers Mac, great information, and great to see the thirst for knowledge to make our training better (suffering harder? )
I’ve noticed the lower heart rates in a tough sesh, lie awake till late even though I’m toast, and my watch is laughing at the HRV and sleep results.
I love training data and numbers I don’t yet understand, looking forward to this study.

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Sir Mac - I have lots of data in my garmin connect files that cover all day, including rides before and during the TOS. I don’t mind sharing it, but I have never tried to export it. Would it be useful?

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On here with the same account as SUF, happy for you to get any info you want from there. If you need anything signed happy to do that, otherwise help yourself.

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