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About Training Stress Score


What is TSS Training stress score

You might see all these abbreviations like TSS, IF, CTL, SC, FTP.. on wither your training peaks and strata or even head unit. They can get pretty confusing and make you wonder what they really are. Well today we are going to get familiar with TSS and IF… Training stress score and intensity factor. These go hand in hand when it comes to training and building to be stronger.

First lets explain what exactly TSS means…

When it comes to training metrics, most programs will calculate this using TSS or the Training Stress Score. There are many things TSS represents in a workout and many misconceptions within the endurance community about this metric. So what does it all mean?

TSS is an estimate of the training load created by a workout based on intensity and duration. TSS is calculated by using both IF (intensity factor) and time, to determine how “hard” a training session was based on the magnitude of the physiologic adaptations to training. In simplest terms, TSS determines the “cost” a workout has had on your body. Typically the higher the calculated TSS score, the more fatigued you will feel.

So first what is intensity factor (IF)?

Intensity Factor (IF) is an indication of how hard or difficult a ride was in relation to your overall fitness. IF values are calculated by taking your Normalized Power (NP) and dividing it by your Functional Threshold Power (FTP).

Typical IF values can range from 0.75 to 1.15 with 0.75 being the easiest and 1.15 being the hardest.

Now dont confuse normalized power with average power. These two are a bit different.

let’s take two different efforts of 1 hour. First, a steady 1 hour ride on a trainer with little to no variation in output at an average of say 200 watts might be a fairly easy ride for a particular rider. Next, consider a 1 hour ride on a hilly course, and insert 10 to 15 short intervals where the same rider is putting out 300 to 400 watts for 15 seconds to 1 minute at a time followed by easier pedaling below 200 watts for recovery. With all the higher highs and lower lows, the athlete may still average 200 watts.

Normalized Power is calculated using an algorithm that is a little complex, but in a nutshell takes into account the variance between a steady workout and a fluctuating workout. The resulting value is an attempt to better quantify the physiological “cost” of the harder “feel” of the variable effort. For a highly variable workout, NP can be much higher than average power, where for a very steady workout, NP and average power are equivalent or very close together. A relatively high NP is showing that the workout had a lot of variation, and was harder physiologically than what average power may reveal.

So back to intensity factor:

The IF system compares the energy exerted from one training session to another and lets you check for changes in your FTP. A ride of 1.0 would be equal to your FTP. An IF value of more than 1.05 for a one-hour race typically means that a rider's FTP is now higher. Therefore, changes in FTP can be revealed without the need for frequent formal testing.

Your NP is 300 Watts. Your FTP is 310 Watts. The IF for that ride would be 0.97.

If the same ride is performed later in the year and your FTP had risen to 320 Watts, your IF would be 0.93. This would mean the same workout required you to exert less energy

Typical IF values for various training sessions or races are:

  • Less than 0.75 recovery rides

  • 0.75-0.85 endurance-paced training rides

  • 0.85-0.95 tempo rides, aerobic and anaerobic interval workouts (work and rest periods combined), longer (>2.5 h) road races

  • 0.95-1.05 lactate threshold intervals (work period only), shorter (<2.5 h) road races, criteriums, circuit races, longer (e.g., 40 km) TTs

  • 1.05-1.15 shorter (e.g., 15 km) TTs, track points race

  • Greater than 1.15 prologue TT, track pursuit, track miss-and-out

So with that lets get into what TSS is… 

How is TSS Calculated?

TSS = (sec x NP x IF) / (FTP x 3600) x 100

sec: the total number of seconds in the session

NP: Normalized Power (more on this in a bit)

IF: Intensity Factor (more on this in a bit)

FTP: Functional Threshold Power (power you can hold for the 60-minute duration)

3600: total number of seconds in an hour

For example, a 60-minute ride at FTP (functional threshold power) would yield a TSS score of 100.

it is also important to distinguish that NOT all TSS scores are the same.

TSS is a good tool to use for analyzing trends in your training. Whether this is weekly, monthly, or within a training block. Following and analyzing your TSS scores can help get a glimpse into the fatigue levels your body is going to experience. Being able to recognize when your fatigue levels are accumulating and staying at a sustained high level for weeks at a time can help you avoid overtraining.

If you continue to train with increased fatigue for long periods of time, your body will be begging for rest. This is why it can seem easy to perform a difficult interval workout during the first week back post-recovery, versus performing the same session at the end of a three-week training break – accumulated fatigue has set in.

When you are able to track and recognize these patterns, you can then recognize when it is time to take your foot off the gas pedal and take some rest.

While metrics can oftentimes be confusing and make us stress over “hitting the right number,” it is important to remember that there are pros and cons to always relying on metrics. TSS is a great tool to get a gauge of how hard or easy an effort should be, but it is not concrete or set in stone that this is in fact, how your body perceives it. Having the knowledge of understanding metrics like TSS can help us as athletes make better-informed decisions when it comes to our training than relying on the data alone. TSS can help us track trends that ultimately help us learn when our body needs rest more than anything else. Pushing past our body’s limits is a good way to gain fitness, but too much for too long is when we get ourselves into trouble.

Now This can seem like a lot of information and can almost be too much to want to grasp, But I believe that the more knowledge you gain abut yourself and the measure of your training, the better you can understand the reasoning to how and why to get stronger and why might a coach (me) prescribes those killer workouts or these easy weeks. It gives YOU a better understanding of how you can be aware of your training rather than thinking to go by a lan you saw.. Everyone is different and different ways things work for different people.

So TSS is a great tool for catering training to your goals and getting stronger. Done properly, you will be well on your way to success! Now this is where I emphasize having a coach. From my years of experience as both a professional athlete and coach, It helps to have guidance and someone to manage your TSS and other metrics to make your training SPECIFIC for you. Thats Why I am here. Please sone hesitate to sign up today or reach out to me with any questions. I also have consultation calls to tackle all questions and create a base program for you.

Happy Training!

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