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The Tails and Turmoils of TSS®

With winter training load typically high around this time of year, particularly as we enter the start of the new year, the shortest day is now behind us. Motivation has started to creep in as we can smell the start of the racing season.

I have had many conversations about TSS® with many athletes. Many seem to chase it through the lens that it is the elixir of performance, the holy grail of performance metrics, asides from your threshold power of course. With this notion that it represents their physical capacity is. With the mantra that more is more and higher means better.

"Mine is not high enough"

"It isn't moving"

"I want a score of X"

I'm sure all the sounds familiar, I've been in that very situation where I was purely focused on the metric rather than the bigger picture, i.e. the context of what I should be aiming for.

"Context in terms of the Performance Demands of my event"

This little article isn't a case of a shining a negative light on TSS. It's more about context, it is a tool, it's about understanding what it means and how to use it. Particularly when it comes to the performance management chart. There isn't much research looking at TSS, there is continual debate amongst physiologists and coaches about definitions of threshold particularly between functional threshold power and CP. Particularly situations about what they represent, how to measure them and why one is superior to the other. I'm biased for CP but we have to also respect that cyclists have been familiar with FTP for over the last two decades. Both have pros and cons, but we will go over this at another time.

But these articles aim to simply point out the nuances with these metrics, If you don't agree, drop me an email, as I love a good discussion.

First, TSS is that it is based on FTP, but you could replace it with your CP, I won't tell anyone if you don't! Next, it is then formulated from your normalised power. during a ride. Essentially a weighted 30s rolling average, see below.



Your normalised power is divided against your FTP, giving you an intensity frequency. Which is below. Essentially what % of your FTP was your ride at.


Then the next part is how TSS is calculated.


So there we have it. If you want to take a look at some research, have a read of the PhD Thesis by Teun Van Erp - 10.13140/RG.2.2.26089.44643 on "Load, Intensity and Performance in Professional Road Cycling"


This then goes into how other measures are calculated, which is simply a 42-day weighted rolling average [CTL], 7-day [ATL] and the difference between the two known as [TSB]. Chronic training loads, acute training load and training stress balance respectively. These form the performance management chart. see here

It was originally developed/inspired by the work of Eric Banister,


Here is a long article surrounding the performance management chart.

With the Maths out of the way for the most part, most are under the assumption that a higher TSS represents a better session, i.e. the higher this value is the more I gain from it. Similarly, if my CTL is higher I'm getting stronger and will be fitter.

This is where context is key. This is one metric, it promises a lot, but in reality, it says very little.

Rider A has a CTL of 100 and Rider B has a CTL of 75 who is stronger?

Simply, you don't know. All you know is their individual CTL value, attained in every way their training evoked that number. In my opinion, I see and view it as a stress guide, how much stress in your lifestyle, with your time commitments can you cope with. CTL is an arbitrary unit, it has no value, whereas power has a value of watts (W) speed has kmh etc.

Let's say two riders over a week have two full rest days and one attained a weekly TSS score of 500 and the other 650.

Athlete A Athlete B






















Again, who will be stronger? let's say they repeat this for the next 12 weeks, with two recovery weeks at 1/2 their load for example.

Again, just off CTL, we can't tell. The athlete with the higher weekly TSS, you could argue can have a training load. Well maybe. Let's for argument's sake say the one with the lower weekly TSS has intense sessions close to the threshold, and the other one simply rides in zones 1-2 all the time.

We are likely to think of athlete A, which may be right. You also need to consider how they accumulated their TSS. For a steady endurance rider 3-4 hours of around 180-200 TSS will be very different to 2.5 hours of intervals of a similar TSS value, this is where it IF can come in handy to look at the relative intensity of that session and it will be more appropriate to also factors in kJ (total work) and kJ/kg to normalise against body weight.

Another metric to track, particularly when more intense work is present is work done above threshold, as this intensity often comes with high fatigue and this may not be that well reflected in TSS you could have a week of 500 from steady efforts and conversely a 500 work from some hard intensity. weekly values are the same but you will accumulate more fatigue from the intensity, this will all feedback into CTL.

Get to the point please

This value on its own isn't all that useful, particularly not a useful one to chase. particularly for riders with less than 12 ish hours. Your limiting factor here will be time and how much you can cope with given everything else going on in your life. Training is just one stress, and each of us can cope with a different amount of training stress and total stress from things such as work, life, and social events. Your ability to fuel with sufficient nutrition and sleep will also determine this as well. But your ceiling will be volume so CTL will be slow to move at one point if you have saturated your training volume.

But, that is fine, you can make a lot of gain on 10-12 quality hours. Full-time riders will naturally have a high CTL as they do a lot of volume around December/January. It is not uncommon to be on 20-30-hour weeks.

Often winter aims to develop a strong aerobic base, but let's say an intense long zwift race of 180+. This will have a larger interaction across the energy systems and you will think this is a good 'winter base ride' as it was long and hard and may be doing more damage than good. I will add each situation is different. While a low TSS zone 1-2 ride might not seem appealing, it's such an important part of the process.

The aim for many, in a physiological sense, is to put the aerobic adaptations in place such as a rightwards shift on your first lactate threshold, capillary density around type 1 muscle fibres, mitochondrial biogenesis etc. It often takes a while for you to 'feel' these changes, and many prefer the more intense session as you 'feel' stronger sooner. but these gains go as fast as they come, intenseity too early often leads to burnout and a lack of progression through the season. See below a nice lactate profile. Essentially we want to push the curve to the right. LT1 is a key performance factor, we have a manuscript with evidence suggesting its importance. Also, look here

TSS use

Despite the above, it can still be a useful tool. But think of it as your score, you can look for trends, and understand how much stress you can cope with. Do you see more fatigue appearing after a particular type of week? How many days does it take you to feel good to go after a 200, or 300 TSS day? Forget the meaning of 'fitness' in its crudest sense but consider it as a load management tool to help you manage and prescribe training.

Racing & Recovery Weeks

It can be a great way to have a good estimate of how to reduce the load in a recovery/de-load week and how to conduct your taper for an event.

it is about context

As is with most things. Use it as a tool, in your coaching or athlete toolbox to help guide your training. But it should be in the context how, your aims, your coals, your training time, how much you can cope with, and your training history.

It isn't just about the training, it's about the quality of it, its the consistency of it all together. Are you getting enough sleep? Athletes often undervalue sleep but are quite happy buying the latest bit of tech. The other priority is sufficient fueling, are you feeling enough?

I can honestly say, that two huge improvements anyone can make in their training is to sleep more and train for the work required, particularly in those longer training sessions.

Use it wisely

It can be a really handy metric if used appropriately, but it is not the be-all or end-all. Consider what your performance demands are. where you are now and thus training is about bridging that gap.

Keep it simple, don't neglect the basics

Performance demands will overlap, but consider, power demands, duration, technical and skill elements etc.


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