What is TSS in cycling?
TSS (Training Stress Score) is a power-based metric that quantifies the total physical stress a cycling session places on your body. It takes into account both the intensity of the effort (via Intensity Factor) and how long you rode. A score of 100 TSS is roughly equivalent to a maximal 1-hour effort at your FTP. See also our calculate Watts per Kilogram, Weight (kg) & Zwift Category — Watts per Kg.
How is TSS calculated?
TSS is calculated using the formula: TSS = (duration in seconds × NP × IF) ÷ (FTP × 3600) × 100, where IF (Intensity Factor) = NP ÷ FTP. You need your Normalized Power (NP) from your ride data, your current FTP, and the total ride duration in seconds.
What is a good TSS score per ride?
It depends on your goals and training phase. A TSS under 150 is a low-to-moderate ride with quick recovery. Scores between 150–300 represent harder efforts needing 1–2 days of recovery. Anything above 300 is very demanding and may require several days to fully recover from.
What is Intensity Factor (IF) and why does it matter?
Intensity Factor (IF) is the ratio of your Normalized Power to your FTP. An IF of 1.0 means you rode at exactly your threshold. Values below 0.75 are easy/endurance rides, while values above 1.05 indicate a very hard, short effort above threshold. IF provides context for how hard you actually rode relative to your fitness. You might also find our use the Cycling Power Zones Calculator useful.
What is Normalized Power (NP)?
Normalized Power is a weighted average of your power output that accounts for the physiological cost of variable-intensity riding. It's higher than average power on rides with surges and climbs, and better reflects how hard your body actually worked compared to a flat average.
What weekly TSS is appropriate for cyclists?
Beginner cyclists typically manage 200–400 TSS per week, intermediate riders 400–600 TSS, and well-trained racers may accumulate 800–1,200 TSS per week. Increasing weekly TSS by more than 10–15% too quickly risks overtraining and injury.
How does TSS relate to CTL and ATL?
CTL (Chronic Training Load) is a rolling 42-day average of daily TSS, representing your long-term fitness. ATL (Acute Training Load) is a shorter 7-day average representing fatigue. The difference between CTL and ATL gives you TSB (Training Stress Balance), which indicates whether you are fresh, fatigued, or peaking. These metrics are used in platforms like TrainingPeaks and TrainerRoad.
Is TSS accurate for all types of rides?
TSS is most accurate for rides where you have a valid power meter reading. Without power data, you can estimate TSS using heart rate-based metrics (hrTSS) or perceived exertion, but these are less precise. TSS also doesn't fully capture the neuromuscular stress of sprinting or the mental fatigue of technical riding.