Of the great variety of data that powermeters provide for the training of an athlete, the TSS® is one of the most important, is one of those that the triathletes and cyclists must know to be able to understand their feelings perfectly and that at the time indicates a key data that has been scientifically well contrasted.

As a reminder, the TSS (Training Stress Score®) indicates the stress (load) to which the body is subjected in a certain period of time. In other words, it would indicate the physical requirement that a stimulus would imply for the athlete, a key information to plan his or her season, training and races.

The TSS is obtained from other individual parameters among which the FTP, the NP® and the IF® have to be measured. In addition, time also intervenes in the equation. Once calculated, the TSS yields a figure that the higher it is, the more stress it indicates. Thus, a session with a TSS of 300 informs us that the organism has been subjected to more demands than in a session of 100.

The exact formula is presented like this:

TSS = (seconds * NP * IF) / (FTP * 3600) * 100.

This number has resulted in one of the key variables ​​to take into account the two major variables of training: the quality (intensity) and the quantity (time) of a stimulus. Therefore, the more intensity and/or more time, the more the TSS grows. And this is where it is important to stop, analyze and relativize.

The coach or the athlete must know how to properly assess each TSS data since there is a lot of information to interpret. For example, if in two workouts a TSS of 90 is reached but those sessions have been one and two hours of pedaling respectively, it is necessary to analyze another variable that allows us to relativize that TSS reached.

As in everything that happens around the powermeter, the great wealth of information it provides is based on the need to cross several data to obtain a final conclusion. For this reason, to correctly assess the TSS that serves as an example (90), the intensity factor (IF) is used, that is, the data that indicates to what intensity the effort has been made in comparison with the FTP (Funtional Thresold Power) of the athlete.

Thus, in a session with a TSS of 90 that has been prolonged 60′, the IF will be high, around 0.95 (which would indicate a training in Zone-4) while in the session with the same TSS (90) but which has been two hours long, the IF will be around 0.67 (that is, a training in Zone-2).

But besides being able to use the TSS in a precise way to plan, control and analyze training loads, another great advantage is that it allows to know exactly the demands that a competition supposes. For example, in the 180km of the IRONMAN bike course, the ideal TSS that a triathlete must reach in order to complete his or her best marathon and thus achieve his or her best final time in that event has been well described. That number varies (depending on the qualities of every athlete and the time he or she spends in the bike course) between a TSS of 227 and 309 (data published by Joe Friel in his book Going Long).

However, if we talk about road cycling, a long distance race like the Quebrantahuesos, can lead a cyclist to accumulate a TSS of more than 400-450 at the end of 197.98km. Of course, the cyclist must not continue to run after finishing his or her bike course, so he or she has to pedal at his or her maximum effort (relative to distance/time) throughout the QH.

From there, the coach must plan during the season workouts that are facing that TSS that will reach the athlete on race day, so that his or her preparation is totally specific to conquer an IRONMAN or a road cycling event.

Individualizing the training to the maximum through the TSS is possible and thanks to this, each athlete can achieve his or her best level at the key moment of every season, when competing at the highest level of every racer is the goal.