Applying the Numbers Part 2: Training Stress Score

BY Joe Friel

In part 2 of Applying the Numbers, Joe Friel explains how to use Training Stress Score® (TSS®) to estimate increases and decreases in your Chronic Training Load (CTL).

In Part 1 of this series I addressed the question posed by a TrainingPeaks subscriber of how high should his Fitness level (CTL) line on the Performance Management Chart (PMC) be. I tried to explain that such a number can’t be proposed without knowing a tremendous amount of background info on the athlete. The answer depends on a lot of individual variables. The best way to use Fitness is to pay attention to the trends over time. A rising Fitness line shows improvement while a falling line indicates a loss of fitness. That’s the primary thing we want to reap from Fitness.

But I suggested in that blog post that Fitness can be used to determine how much TSS® you may aim for in any given workout. This is an imprecise “science” and is really just giving you a general target for each session. Here’s how to do it.

Typically athletes have three basic and general categories of workouts they do on a weekly basis. Let’s call them “hard,” “moderate,” and “easy.” What most of us do is follow a hard workout with an easy one and occasionally insert a moderate session. What should the TSS be for each of these general categories? Here’s a quick way to estimate them based on your Fitness for any given day.

• Hard workout: Add 50 to 100 percent to Fitness
• Moderate workout: Add 25 percent to Fitness
• Easy workout: Subtract 25 percent from Fitness

Let’s look at a couple of examples. For the first example, let’s say the athlete’s Fitness is a rather high 100 (measured as an average of TSS for the last 42 days and expressed as “TSS/d”). Using the above ballpark values this athlete’s daily workout TSS categories would be…

• Hard workout: 150 to 200 TSS
• Moderate workout: 125 TSS
• Easy workout: 75 TSS

How about an athlete whose CTL is 50? His or her workout three workout categories would be:

• Hard workout: 75 to 100 TSS
• Moderate workout: 63 TSS
• Easy workout: 38 TSS

Again, these are not meant to be unquestionable values. There may be days when you’re feeling great due to a few easy days or even days taken off from training and feel up to doing a hard session which produces a TSS greater than what is suggested above. Or the opposite is also likely to occur when you are too tired to do even a workout at 25 percent below your CTL. These are meant only to be ballpark numbers. They aren’t carved in stone and backed up by impeccable research. But they generally work.

In Part 3 I’ll discuss your PMC Training Stress Balance and how you can use real numbers there to manage your performance.