Power Training Terminology Explained: What’s TSS?

By Martin Sigrist

Takeaway: Power based training introduced a variety of new concepts and acronyms. This is the first of an occasional series that will explain these in plain English. TSS or Training Stress Score is the first as it is fundamental. It is an objective measure of how much stress a workout causes. This is of importance because the essence of getting fitter through training is to put stress on you body so that it adapts and becomes fitter. TSS allows this to be planned and measured in a precise and effective way. With practice it can allow an ideal balance to be developed between workload and recovery.

“Training and Racing with a Power Meter” came out over 15 years ago (and was revised in 2019). It was revolutionary, Hunter Allen and Andrew Coggan came up with a new approach to training and because it contained new ideas it needed new ways and words to describe them.

The result was a plethora of TLAs (three letter acronyms). FTP is probably the most well known, but there are many more.

I’m a scientist so I’m comfortable with swimming in an alphabet soup if there is a payoff in terms of new ideas and precision. But I appreciate that a foreign language can be off putting.

This is a shame as I think there is value, in understanding power based training concepts because this can give insights that can allow more intelligent and focused training. That may result in better use of time or ensuring that input in terms of training is a best fit for the desired output, whatever ambition is being pursued.

And sharing a common language can help with communication and sharing understanding in, for example, RBR articles.

So this will be the first of an occasional series that will describe some of power based training’s concepts. The approach I will take is to try to describe in plain English what a concept is along with some suggestions of how it can be used in practice, rather than get bogged down in too much jargon.

Each will take the form of a few plain English sentences describing what it means and what it is used for. then some deeper explanation and finally some practical advice on how to use it, some useful even if you don’t own a power meter.

I’ll start with TSS

TSS – In plain English

TSS is Training Stress Score and is a number ranging from low 10s to multiple 100s that gives an objective, independent measure which represents how much stress (and so how tough) a workout was. As a rule of thumb a TSS=100 is the same as doing one hour as hard as you can sustain for that long.

TSS is used in planning and executing a training plan. Each day of training will have a target TSS which should reflect your ability to absorb and improve from workload and limitations in terms of training time.  

TSS – An Introduction

As its name implies TSS is a number that provides a score that measures how much stress a training session puts on your body. This cuts to the heart of what training is all about. It’s the paradox of doing yourself “harm” so that when you recover you get stronger. “Stress” is good. The more the better (with some caveats but I’ll deal with them later).

TSS is an excellent example of just why power based training is so powerful. It is an objective, independent measure of how hard a workout is.

There is nothing else that does this. Every other measure is any or all of inaccurate, dependent on the individual or not a measure of what you are actually trying to improve.

In order to understand why TSS is such a useful tool it helps to understand a bit of how it is calculated. TSS takes your FTP as a baseline and sets an arbitrary score of 100 if you ride at exactly your FTP for exactly 60 minutes.

This, in itself is revolutionary. It means that you can take two cyclists at extreme ends of the ability scale, a rank beginner and a world class pro. If they both do a workout and have a TSS of 100 then you know that both have experienced roughly the same amount of training stress and that it was the same as if they had done an hour all out at their threshold power. TSS allows apples to be compared to apples in terms of stress, which is one of the most important factors needed both the plan and undertake a training program.

The second key thing to know about TSS is that not all training minutes are equal. This is obvious, one minute all out is much harder than one minute easy riding. Indeed, it is much harder than several minutes of easy riding.  TSS measures every second you ride and compares the power for that second with your FTP. If you are riding under FTP then the TSS increases slowly, if you ride above then it increases much faster.

To give an example for an FTP of 300W below is the TSS for 5 minutes steady power

150=2 TSS, 200=4 TSS, 250=6 TSS, 300=8 TSS, 350=11 TSS, 400=15 TSS, 450=19 TSS, 500=23 TSS

(taken from https://www.formbeat.com/tools/tss-calculator )

So a hard interval session that lasts only an hour or so can result in a higher TSS than an easy three hour ride. Intuitively we know this and our legs will let us know the next day too. TSS makes it possible to be far more precise.

TSS Need to Knows

There are a few things about TSS that you need to know.

1. People differ, some are better at short sharp efforts, others a long steady ones (these are called “phenotypes” in power based training). TSS does not take account of this so it is possible that two individuals could do the same training session with the same TSS and the effect on each would be different. So TSS is a measure but it is not a magic measure. Just blindly aiming for high TSS is not a training plan. The TSS must be appropriate. So a sprinter would aim to get high TSS scores by doing sprint training and a TT rider by doing longer intervals. Provided they do that then if they can increase the TSS they can handle in each training session they will be likely to improve.
   
2. If your FTP changes then your TSS for the same power will change. This is obvious given the method by which it is calculated and the way training zones work but it does mean having to recalibrate expectations if, as hopefully will happen, you get better and your FTP goes up. The plus side to this is that TSS helps check your FTP is correct. How “hard” you find a session should remain constant and corelate to TSS. 100 should feel like 100 regardless of whether your FTP was 200W as a beginner or 400W now. (Note: it may not be sensible to change FTP used for TSS calculation every time it changes. I’ll explain why in a future article.)
   
3. TSS can be gamed. It is possible to get high TSS scores by riding in a certain manner. The actual training benefit of these may be less than the score indicates. Again the message is that TSS is not a magic bullet, getting full use out of it requires an intelligent training plan not just chasing TSS scores.
   
4. Recovery for the same TSS may vary between people. If two individuals do a training session of 150 TSS it does not mean they will react in the same way. TSS is an objective measure of input into the adaptive process, but the output (i.e. what you are training to improve) will differ by individual for all sorts of different reasons. Still, just having a consistent measure of input is a great leap forward.

In summary, you want your training sessions to produce as much TSS as possible in the time you have available, but done in a way that fits you as an individual, in terms of time available to train, rider type and how you react to training load. (I’ll return to this point later in future articles that deal with long term measures of training load.)

Suggestions on how to use TSS

TSS is an essential building block in power based training so will crop up again in other topics. Some suggestions that I would make now are

1. Plan your workouts using TSS:  The purpose of a training plan is to schedule time where you will stress your body. It makes sense therefore to know in advance how much stress you want to do so a plan should include an estimate the TSS of each workout. (While respecting the point made above that the TSS should be “good” TSS, relevant to your personal training needs.) There are tools that can help do this but a spreadsheet or even a paper plan is better than nothing.  Planning is an iterative process, they key thing to do is make a first pass then see how it goes in practice and revise accordingly. If totally unsure just start by assuming you will do 60 TSS per hour of training then see what actually happens. Is 60 too much or too little?
   
2. Gauge how you recover based on TSS: Everyone is different and one very important difference when training is recovery post workout. Recovery time will correlate to TSS in some way. So over time get used to seeing how much time it takes to get over a training session. Does, for example, a session with 100 TSS take much less time than one with 130 TSS? This will help in planning future training.
   
3. If you can hit your TSS target then you don’t need to worry about “overtraining”: A follow up to the two points above is that you can use TSS to judge how you need to recover. If you plan workouts based on TSS and can hit the target TSS score without difficulty then it’s a sign that you can increase your expectations in how hard you can workout and/or reduce your recovery time. On the other hand if you struggle to hit TSS targets then it may be that you need to either reduce them or schedule more recovery.
   
4. If you are time pressed aim to maximize TSS in workouts: If training time is limited then it can become difficult to stress the body sufficiently to cause adaptation. My personal opinion is that unless you have 15 hours of more to spend training each week every hour spent training should be looking to generate as much TSS as possible while respecting the workout target in terms of training zone. So for short interval sessions only do a short warmup before getting into the first set, keep rest intervals short and only do a minimal cooldown. For longer steady efforts aim at the highest power you know you can sustain. The higher in the target zone you go the more TSS will be generated, which should be a good thing.
   
5. Guesstimate TSS for other activities which may cause stress. If you have to do tasks that are physically demanding or if you cross train and do sports other then cycling then you can estimate TSS and include it in your plan to help gauge your workload and give you a feel for how much recovery you need. This can be done by simply using effort or a HR monitor. A simple table that uses both can be found here https://www.trainingpeaks.com/learn/articles/estimating-training-stress-score-tss/

Email me on [email protected] if you want more info on this or any topic I have raised. I make take a while but I will get back to you.)

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Now among the world’s fittest sexagenarians Martin Sigrist started riding on doctor’s orders in 2005 and had to push his bike up his first hill. Next year he soloed the Tour de France. He has since experienced every form of road cycling from criterium to ultra endurance. His ongoing mission is to use the latest in science and technology to fight a, so far successful, battle against Father Time.