Overtraining and undertraining are two sure ways to end up sick or off the back on your group rides. For many of us though, it’s hard to quantify the training stress that we subject our bodies to. Years ago, cyclists measured training stress based on the number of miles accumulated in a given period. But today we have TSS—an easily quantifiable metric that tells you just how much of a training load you’re placing upon your body. And what’s more, with your Tacx smart trainer it’s automatically calculated for you!


TSS stands for Training Stress Score. It measures the load that you place your body under while training or racing. Many people equate training load to fitness. But it’s really how you respond to training stress that dictates your fitness—something that’s a source of confusion for many.

TSS is a unitless measurement. A TSS score of 100 equates to one hour ridden at your functional threshold power (FTP). From there you can extrapolate, one hour at 50% of FTP would be 50 TSS, while 3 hours at 80% of FTP would be 240 TSS. But of course, with the varying intensity of our rides, the calculation never works out so conveniently.


The TSS calculation takes intensity and duration into account and several methods exist for calculating it. Here’s how it’s done.

TSS=((Workout duration in seconds * Normalised Power * Intensity Factor) / (FTP * 3600)) * 100

But there’s no need to get a calculator out after every workout as all software solutions running with power meters will make the calculation for you.


Normalised power represents an estimate of the power you could have maintained for the same energy cost if it had been kept constant throughout the ride. Normalised power factors in the lulls during a workout or race that throw the average power calculation off. It provides a representation of the overall intensity and is calculated automatically by the software running with your power meter or smart trainer.


Intensity factor takes the differences in fitness between individuals into account. It is calculated by dividing normalised power by FTP. FTP varies between individuals, and also varies across the entire season in an individual athlete. IF provides a way of quantifying the effort and allows you to compare efforts regardless of FTP at the time.


One useful benefit of TSS is in gauging just how much recovery you require after a given workout. We all know just how tired our legs can be after a hard workout. A quick glance at the accumulated TSS helps us quantify the resulting time we require for recovery after such a ride.

  • <150 – Riders are generally recovered by the following day.
  • 150-300 – Fatigue may linger for a day, but recovery is generally complete by the 2nd day.
  • 300-450 – May require up to 2 days of recovery.
  • >450 – Several days of recovery required.

The Tour de France is the pinnacle of cycling, and the beauty of TSS is that you can compare yourself to the pros. But before you get any ideas, remember that they have much higher thresholds than us mere mortals. There are road stages in the Tour where they average as little as 100 TSS, and that increases up to 350-450 TSS on the big mountain stages. And they do that for 3 weeks with only 2 rest days!


There’s stress and there’s strain. While riding at 75% of your FTP for 4 hours clocks up the same TSS every hour, the first hour won’t be the same as the fourth. Your body is under much greater strain come hour 4.

TSS is only that straightforward metric if your training is uniform. Triathletes training at the same intensity day after day can easily quantify their training with TSS. But the same can’t be said for road cyclists who train their sprint one day and their aerobic capacity the next. Intensity needs to be factored in when you analyse TSS because it’s your response to the strain that matters much more than cumulative TSS.


Many cyclists view their training load solely through the lens of TSS. They assume that their “bike time” is the only factor affecting performance. But as we all know, there’s often a lot more going on. Stress at work, a newborn baby and 3 hours sleep, or the incorporation of strength training into your routine will all affect the strain you subject your body to. Be mindful of what’s happening off the bike. If you find your performance dipping, don’t immediately assume it’s your training routine that’s to blame.

Performance rules, so try shifting your focus from the continuous escalation of TSS to how you’re performing. Decreasing TSS and increasing performance is much healthier than the opposite.


On one of those long “relaxed” Sunday club runs, your TSS can escalate wildly. It’s all too easy to put in a 300 TSS ride with little to no structure behind it. At Tacx, all of our smart trainers measure power. Used with our structured training plans and Tacx Training app you can really begin to get a handle on training stress.

The precision offered by this method of training helps ensure you minimise those junk miles and the subsequent accumulation of training stress that won’t factor into improved performance. By consistently following a custom training program you’ll have all the data you need to really understand what training stress you require for optimal performance.