So what to do with this Training Stress Score? What is it good for and how could it help you to get better? Let’s explain it all in this article.
The idea of training is to put stress on the body. A workout fatigues the body, after which your body realizes it should be better prepared the next time. We have explained this principle also in The Basics of Training. So during the recovery after a workout, your body adapts and gets better. Depending on how hard the workout was for your body, you should take a certain time to recover before undertaking a new workout. Based on this principle it is quite important to evaluate how hard a workout actually was. Workouts come in all kind of shapes and sizes. We have hard and intense workouts or long and easy ones and everything in between. So it seems almost impossible to compare different workouts. Exactly here is where the Training Stress Score (TSS) comes in play.
The idea is quite simple. Riding for one hour on your functional threshold power (FTP) based on the normalized power will get you 100 points. So riding two hours on half your FTP will give you the same 100 points as half an hour on twice your FTP (which should be humanly impossible, but is just for argument's sake). So the formula is actually multiplying the Intensity Factor with the duration of the ride in hours and multiplying it with one hundred. With this number you can compare a short intense interval ride with a long endurance ride and the impact it has on the body. Looking at all the training stress scores over the last weeks or months will give a good indication of how much you are actually doing.
Back in the day without power meters or training stress scores there was only just the amount of hours someone trained over the last weeks or months, without looking at the intensity. That often resulted in just doing more and more hours on a lower intensity, despite the fact that doing less hours but at a higher intensity is also a way to increase the workload.
Increasing the workload in the right manner is actually one of the most difficult concepts of training. First of all a workout should be properly timed. When the body is not enough recovered from the last workout, exercising too soon will only fatigue the body more. Also, when a workout was too hard, the recovery period takes too long and the body will not adapt at all. So training stress score helps a lot in monitoring the workload and making sure not to overdo it.
One really important side note needs to be made here. If two workouts end up with the same training stress score, that doesn’t mean the training effect is also the same. A short intense strength exercise can result in the same training stress score as a long slow ride to enhance fat oxidation. The training stress scores are the same but the training effect and the way the human body adapts are completely different. Therefore it’s still important to look both at the intensity factor as the training stress score when you monitor training load.