Key Takeaways
- Training Stress Score (TSS) quantifies the overall training load of a cycling session based on duration and intensity relative to your FTP.[1]
- One hour at FTP equals a TSS of 100 by definition — this anchor point makes comparisons between different rides straightforward.[1]
- TSS is calculated using the formula: TSS = (duration × NP × IF) / (FTP × 3600) × 100, where IF (Intensity Factor) = NP / FTP.[1]
- Tracking weekly TSS accumulation helps manage training load progression and avoid overreaching — a key application of power-based training.[2]
How TSS Works
Training Stress Score was developed by Allen and Coggan as a way to objectively measure the total physiological cost of a ride. The formula combines both how hard you rode (Intensity Factor) and how long you rode (duration) into a single number.
TSS = (Duration_seconds × NP × IF) / (FTP × 3600) × 100
Where IF = NP / FTP
When using average power for steady-state rides, average power serves as the NP value. For variable-effort rides — group rides, criteriums, interval sessions — Normalized Power provides a more physiologically accurate intensity metric.
Your FTP is the foundation of TSS. If you haven't tested recently, use the FTP Calculator to estimate your current threshold from several test protocols.
Practical Application
TSS enables you to plan and evaluate training at a glance. A 90-minute endurance ride at 65% of FTP might yield a TSS of ~57, while a 60-minute threshold workout at 100% FTP produces a TSS of 100. By tracking cumulative weekly TSS, you can manage progressive overload.
Research by van Erp et al. (2019) demonstrated that training load metrics like TSS correlate with performance changes in competitive cyclists.[2]
For a full breakdown of how your FTP translates to seven training zones, see the Cycling Power Zones Calculator. To understand how your power output compares across performance tiers, check the Cycling Power-to-Weight Calculator.
Accuracy and Limitations
- TSS assumes your FTP is accurate. An outdated or incorrect FTP will skew all TSS values — retest every 6–8 weeks.
- Using average power instead of Normalized Power underestimates TSS for variable-effort rides.[3]
- TSS does not capture ride-specific stresses like climbing, heat, or altitude — it is purely power-based.
- TSS is most useful when tracked longitudinally (week-over-week) rather than evaluated as a single-session number.
- This calculator provides informational estimates for training planning and personal awareness.
Frequently Asked Questions
Sources & References
- Training and Racing with a Power Meter. Allen H, Coggan A. VeloPress (2019)
- Relationship Between Various Training-Load Measures in Elite Cyclists During Training, Road Races, and Time Trials. van Erp T, Foster C, de Koning JJ. International Journal of Sports Physiology and Performance (2019)
- Monitoring Training Load to Understand Fatigue in Athletes. Halson SL. Sports Medicine (2014)
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