Decoding the Data: An Athlete’s Guide to TrainingPeaks Metrics
If you spend enough time looking at your TrainingPeaks dashboard, you will eventually encounter a confusing array of acronyms: TSS, CTL, ATL, and TSB. While they look like something out of a physics textbook, they are actually the primary tools we use to track your progress and, more importantly, to keep you from burning out.
Here is a breakdown of what these numbers mean for you and how they inform the decisions we make as your coaches.
TSS: The Building Block of Every Session
Every time you finish a workout, TrainingPeaks assigns it a Training Stress Score (TSS). This is a single number that represents how much "stress" was put on your body during that session.
It is calculated by looking at both the duration and the intensity of the workout. For example, a very hard 30-minute interval session might have the same TSS as a slow, two-hour recovery ride.
How we use it: We use TSS to ensure the "dose" of training is right. If we see a TSS that is much higher than planned, it tells us you might have pushed too hard on a day meant for recovery. If it’s lower, we might need to look at whether your zones need updating.
CTL: Your "Chronic" Fitness
Chronic Training Load (CTL) is often simply called your "Fitness" score. It is a weighted average of the TSS you have gained over the last 42 days. Essentially, it represents how much training your body is currently "carrying."
How we use it: We look for a steady, progressive rise in your CTL. However, bigger is not always better. Every athlete has a "ceiling" where the fitness gains are outweighed by the risk of injury. We use this number to make sure we are building your engine at a sustainable rate rather than throwing too much at you too soon.
ATL: Your "Acute" Fatigue
Acute Training Load (ATL) represents your "Fatigue." Unlike fitness, this is a weighted average of your TSS from only the last seven days. It climbs quickly after a big block of training and drops quickly when you rest.
How we use it: This is our early warning system. If your Fatigue (ATL) is rising much faster than your Fitness (CTL), we know a "crash" is coming. When we see this number spike, we will often pull back on your intensity for a few days to let your body catch up.
TSB: Finding Your "Form"
Training Stress Balance (TSB) is the most important number for race day. It is simply the difference between your Fitness and your Fatigue.
A negative number means you are tired (which is normal during a heavy training block).
A positive number means you are "fresh."
How we use it: This informs our "Taper" strategy. To have a great race, we want your TSB to be in the positive range on the morning of the event. If we see you are at -30 the week of your "A" race, we know we need to cut the volume immediately to find your "Form."
Why we look at the trends, not the daily score
It is easy to get caught up in the daily fluctuations of these numbers, but as coaches, we are looking at the trends over weeks and months.
We use these metrics to decide:
When to push: If your Fitness is plateauing and your Fatigue is low, it is time for a harder block of work.
When to pull back: If your Fatigue is at an all-time high and your Form is deeply negative, we will likely add an extra rest day, even if you feel "okay" in the moment.
When to peak: We use the relationship between these numbers to ensure you arrive at your goal race fit, but not fatigued.
The human element
Data is a vital part of what we do, but it is never the whole story. A high Fitness score doesn't account for a bad night's sleep, a stressful week at the office, or the onset of a cold.
We use these metrics as a compass to guide the direction of your training, but we always rely on your feedback to make the final call. The numbers might say you are "ready to go," but if your legs feel like lead, we trust the athlete over the algorithm every time.
Want to see where you stand? Head to your TrainingPeaks dashboard and look for the Performance Management Chart. If you have questions about your current "Form," drop a comment in your next completed workout!