Making Sense of TSS, Fatigue, Form & Fitness

If you’ve ever opened TrainingPeaks and been hit with a wall of acronyms like TSS, CTL, ATL, TSB, you’re not alone. While it might look like alphabet soup, these metrics can be incredibly powerful once you know what they mean.

In this post, we’ll break down the key TrainingPeaks metrics and explain how they relate to your fitness, fatigue, and form so you can train smarter and race stronger.

What Is TSS?

TSS = Training Stress Score

TSS is a number that tells you how “hard” a workout was based on intensity and duration.

Generally the higher the TSS, the longer and / or intense the activity was.

1 hour at your FTP (threshold power or pace) = 100 TSS

TSS helps you compare workouts across disciplines and track your load over time.

To ensure your TSS and other metrics (read on…) it’s essential your performance zones are accurate in Training Peaks. Bad data in = bad data out.

Fitness, Fatigue, and Form: The Big Three

TrainingPeaks uses TSS data to calculate three key metrics:

1. 🧱 CTL – Chronic Training Load (aka "Fitness")

6-week rolling average of your daily TSS
Represents your long-term fitness level
A higher CTL means you’ve built more aerobic capacity and endurance

👉 CTL grows with consistent training, especially with long aerobic sessions.

2. 🥵 ATL – Acute Training Load (aka "Fatigue")

7-day rolling average of your daily TSS
Measures short-term fatigue
Spikes when you increase training volume or intensity quickly

👉 High ATL is normal during training blocks but needs to come down before race day.

3. 😌 TSB – Training Stress Balance (aka "Form")

Calculated as CTL - ATL
A positive number = fresh
A negative number = fatigued

Ideal TSB for race day is usually between +10 to +25, depending on the athlete.

Why These Metrics Matter

💡 These numbers help you (and your coach) answer important questions like:

Am I training enough to build fitness?
Am I digging myself into a hole of fatigue?
Am I fresh enough to perform well on race day?
Do I need to back off or keep pushing?

Instead of guessing how tired or fit you feel, these metrics quantify it and help you avoid common pitfalls like overtraining or tapering too little.

How to Use This In Your Training

🛠 Building fitness?

Gradually increase your CTL each week
Focus on aerobic volume and consistency

🛠 Feeling burnt out?

High ATL with a negative TSB? Time to schedule recovery days

🛠 Tapering for a race?

Reduce volume and intensity to let ATL drop
Aim for a positive TSB by race day to arrive fresh and ready

🛠 Using TrainingPeaks Premium?

Keep an eye on your Performance Management Chart (PMC)
Use it with a coach to fine-tune your training blocks and race tapers

Final Thoughts

The numbers in TrainingPeaks aren’t there to intimidate you, they’re there to inform you. When used wisely, metrics like TSS, CTL, ATL, and TSB can help you balance training and recovery, prevent injury, and show up to your race feeling strong and confident.

TrainingPeaks Metrics Explained