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Training Stress Score – what does it mean?

As a starting point, all this jargon makes an assumption that you measure all your effort using power. Yes, most of us don’t have the luxury of having a power meter on our bike and the closest we get to a power meter is by doing interval training on a power trainer in the gym or at one of our Kickr studios.

Training Peaks has a formula through which they assume what your Training Stress Score is by looking at your heart rate data if you don’t have a power meter and it is shown as hrTSS on your Training Peaks app.

I know there are many people we coach who compare their TSS numbers with their friends and through this they want to compare how hard they train.

Let me say that what I have seen is that your friend’s Threshold Value was either calculated incorrectly, or they are not always honest with you. Why do I say this?

Training Stress Score (TSS)

TSS is your guide towards fatigue and fitness building.  TSS is based on Andy Coggan’s idea that a 100% FTP effort for 1 hour will equate to 100 TSS. (Just think about this for a moment … we are not talking about a 20 min FTP test, we are talking about an 1hour long FTP Test!) If you complete a workout that is 90% FTP for 1 hour (a time trial for example) then you would accumulate 90 TSS points. You can also tie into the RPE (Rating of Perceived Exertion) scale by assigning 10 TSS points to each RPE, per hour.  So, for example if that 1-hour time trial felt like a 9/10, you would rack up 90 TSS.  Note that these values are the same if you’re a Pro or a novice: TSS is based upon YOUR functional threshold and the time spent at a fraction of that threshold.  In this respect, you can see that using a power meter and determining your actual power outputs, interval times and rest times gives you a much more precise value for your TSS.

So, if a friend tells you he or she accumulated 150 TSS points and he or she has only been riding for 1h30 it means that they were riding at equal to their threshold for the full time!! I don’t know many people that can do this if their threshold was calculated at maximum effort. Therefore, my assumption that their threshold is either to low or they are not truthful.

Ultimately, TSS values are the most useful when using them to gauge fatigue and gauge fitness increase (through use of a performance management chart.)  These charts are available in TrainingPeaks and we use it extensively when we calculate your program for the following weeks and planning your race form.

 

 

Note that you may need more or less recovery depending upon the amount of fatigue your body was dealing with prior to undertaking a specific workout.  You know that doing back to back hard workouts leaves you more tired the following day, and that’s a result of accumulated TSS and fatigue.  Your body needs time to adapt to stimuli in order to recover and improve, and that’s why rest is so important and timing of rest days is so important.

So, let’s get back to your program and why your actual TSS is sometimes less than what we predicted when we build your program.

Most of the discrepancies we see are with people who ride without power on their bikes (assuming that they followed the prescribed program) and the main reasons for this is that heart rate is a reactive measurement and if you are tired, the weather is either very hot or very cold, you are stressed or ill your heart rate will not respond exactly in the way that we could have predicted when you used power. So, if you use heart rate, and your hrTSS Score is within 15% of the predicted hrTSS score you are within the band that we expect and you should not worry about it too much. If your hrTSS is outside of 15% of the predicted hrTSS, we need to consider whether your LTHR was determined accurately or that the device you use to record your data, might be faulty.

 

If you use power and your TSS score is different to the predicted value there can only be 3 reasons;

  1. Your device is not recording the data accurately,
  2. Your FTP was calculated incorrectly, or
  3. You are not following the program.

Power is a wonderful thing and there are not many places you can hide.

 

It would be wrong to talk about TSS without discussing its cousin; Intensity Factor (IF).

Intensity Factor (IF)

Intensity Factor is a simple calculation comparing normalized power to Functional Threshold Power (FTP).  (Normalized power is “an estimate of the power that you could have maintained for the same physiological “cost”, if your power output had been perfectly constant rather than variable.”  Basically, if you pedaled the entire ride at a steady pace, with no variations for climbs, descents, etc, this is the average power you would produce.)  What’s important to note about IF is that it helps you to determine how difficult a particular ride or workout has been, and helps you to gauge how specific your training has been.  Take a look at the following IF scores:

Intensity factor Zone Type of exercise
<  0.75 Power Zone 1 recovery rides
0.75-0.85 Power Zone 2 endurance-paced training rides
0.85-0.95 Power Zone 3 tempo rides, longer (>2.5 h) road races and MTB marathons
0.95-1.05 Power Zone 4 shorter (<2.5 h) road races & MTB races, criteriums, etc.
1.05-1.15 Power Zone 5 shorter (e.g., 15 km) TTs, track points race
> 1.15 Power Zone 6 prologue TT, track pursuit

 

As you can see from the values, IF roughly follows power training zones, and you can use this to determine if your ride/workout was within your requirements by looking at the IF.  For example, if your training plan calls for a Tempo ride with muscular endurance intervals and maybe a few threshold intervals, you would expect to see and IF between .85 and .95 (probably closer to .95 due to the threshold intervals.)  If you see an IF of .78, you know that your training was decidedly not hard enough that day (or if it “felt” hard but still resulted in a .78, perhaps your body is excessively fatigued and you’re unable to perform at a higher level without some rest.)  Consequently, if you have a day scheduled that should be endurance work with spinups or single leg drills, yet results in an IF of .88, you’ve trained too hard that day.

By using these IF values, you can temper your training intensity on a day to day basis and keep your training on track.  You can also use your IF scores to determine if it’s time to re-test your threshold.  Consistently breaking into IF scores over 1.0 (for longer training and racing efforts, of course) generally means that your FTP is set too low, and it’s time to go out and test again.  While it’s true that these “normalized power busters” can occur with a properly set threshold, it’s extremely tough to do.

So, if you want to compare how hard a training session was, IF is a better gauge, again assuming that the threshold value was determined correctly. As per TSS, it is much easier to accurately compare these numbers using power. As you can imagine at the end of the Cape Epic your heart muscle will be tired and an IF value based on heart rate will be much lower than what it was at the start of the race, even though your power could still be the same.

To summarize:

  • Make sure your threshold values are calculated accurately
  • Follow the program as closely as possible
  • … as a coach, we look at what kind of TSS score we would like you to achieve for a given period, but we are continually re-aligning your actual TSS with your long-term goals. So, it’s not life-or-death if you do not hit your TSS numbers every training ride.

Johann Wykerd – Head Coach @ Absolute Motion

Email: life@absolutemotion.co.za 

 (Reference: http://tailwind-coaching.com/2016/04/13/training-stress-score-fatigue/)

 

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