The Development of the Training Stress Score

As a coach and a former pro cyclist, I always looked at training from those two perspectives and continually looking for new ways to help my athletes achieve their goals while at the same time using the ‘tried and true’ techniques that I used when I raced. The advent of the power meter or more specifically, the ability to record every second the wattage, heart rate, cadence, etc. has allowed us to discover three key things about yourselves:

  1. Precisely quantify the training ‘response’ to a given training ‘dose.’ See how much you’ve improved (or not).
  2. The ability to understand the ‘response’ of the training ‘dose.’ Learn what training ‘dose’ caused a specific energy system to improve (or not).
  3. The ability to prescribe precisely the training ‘dose.’ How to figure out the optimal amount of intervals, workouts, and rest that give you the best result.

Now, since the power meter has been invented, I can be more specific with the training that I prescribe to my athletes. “Do 45 minutes at 89% of your functional threshold power (FTP) each day” and then within 4-6 weeks, we’ll see the ‘response’. With a power meter we are easily able to see the results of our hard work over time, but, as a coach, I really needed to be able to quantify the exact training ‘dose’ more simply than 2 x 20 minute intervals at FTP. I needed a score.

I shared all this with Dr. Andrew Coggan, and within 2 weeks he came back to me with “Training Stress Score”. Training Stress Score® (TSS®) is based on the simple premise that you score more points for the more time you spend at your FTP and above it. To set the standard, an hour at FTP (as hard as you can go for 1 hour) would be equal to 100 TSS points. Within this TSS, you also had to account for intensity, therefore, a measurement of intensity was given as well, which Dr. Coggan called Intensity Factor®(IF®). An hour at FTP would score an IF of 1.0. These two metrics are used in the TrainingPeaks WKO+ and on and both software products will automatically calculate a TSS and IF for that workout.

By tracking Training Stress Score and Intensity Factor for each workout and over time, this can provide both individual athletes and coaches a powerful tool for analyzing the enormous amount of data gathered by training with a power meter. The results of such analyses can then serve as the springboard for improvements in training and, ultimately, race performance.

Hunter Allen

Hunter is a USA Cycling Level 1 coach and former professional cyclist. He is the co-author of 'Training and Racing with a Power Meter', co-developer of TrainingPeaks WKO+ Software, and is the CEO and Founder of the Peaks Coaching Group. He specializes in coaching cyclists with power meters and is on the forefront of coaching with cycling's newest tool. You can contact Hunter directly at

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