Key Takeaways
- TSS quantifies your workout's training load combining duration and intensity
- A TSS of 100 equals one hour of riding at your Functional Threshold Power (FTP)
- Use TSS to balance training stress and recovery for optimal performance
- Weekly TSS totals help prevent overtraining and guide periodization
- Intensity Factor (IF) shows how hard you worked relative to your FTP
What Is Training Stress Score (TSS)?
Training Stress Score (TSS) is a metric developed by Dr. Andrew Coggan and Hunter Allen to quantify the overall training load of a workout. It takes into account both the duration and intensity of your ride, providing a single number that represents how much stress the workout placed on your body.
TSS is essential for cyclists, triathletes, and endurance athletes who use power meters to track their training. By monitoring TSS, you can optimize your training load, prevent overtraining, and plan effective recovery periods.
The TSS Formula Explained
TSS = (Duration x NP x IF) / (FTP x 3600) x 100
The formula can be simplified to: TSS = (Duration in hours) x IF2 x 100. This shows that intensity has a squared effect on TSS, meaning a workout at IF 0.9 produces significantly more stress than one at IF 0.7.
Understanding TSS Zones
| TSS Range | Training Load | Recovery Time | Description |
|---|---|---|---|
| < 150 | Low | Same day | Recovery ride, easy endurance |
| 150 - 300 | Medium | Next day | Standard training session |
| 300 - 450 | High | 2 days | Hard workout or long ride |
| > 450 | Very High | 2+ days | Race or extreme effort |
What Is Normalized Power?
Normalized Power (NP) represents the power you could have maintained for the same physiological cost if you had pedaled smoothly at a constant effort. It accounts for the fact that variable power (intervals, hills, surges) is more stressful than steady power.
Most cycling computers and apps like Garmin, Wahoo, and TrainingPeaks automatically calculate NP from your power data.
What Is Intensity Factor?
Intensity Factor (IF) is the ratio of your Normalized Power to your Functional Threshold Power (NP/FTP). It tells you how hard you worked relative to your maximum sustainable effort:
- IF < 0.75: Recovery or endurance pace
- IF 0.75 - 0.85: Tempo effort
- IF 0.85 - 0.95: Threshold work
- IF 0.95 - 1.05: Anaerobic/VO2max intervals
- IF > 1.05: Short, maximal efforts
Pro Tip: Weekly TSS Guidelines
Most athletes can handle 400-600 weekly TSS sustainably. Competitive cyclists often accumulate 600-900 TSS/week during build phases. Exceeding your typical weekly TSS by more than 30% increases injury and burnout risk.
How to Use TSS for Training
1. Track Chronic Training Load (CTL)
CTL is your rolling 42-day average TSS, representing your fitness. Gradual increases in CTL indicate improved fitness without overtraining.
2. Monitor Acute Training Load (ATL)
ATL is your rolling 7-day average TSS, representing fatigue. Sharp spikes in ATL suggest you may need extra recovery.
3. Calculate Training Stress Balance (TSB)
TSB = CTL - ATL. A positive TSB means you're fresh (good for racing), while a negative TSB indicates accumulated fatigue (fine during training blocks).
4. Plan Recovery Weeks
Every 3-4 weeks, reduce weekly TSS by 40-50% to allow adaptation and prevent overtraining.
Frequently Asked Questions
The most common method is the 20-minute FTP test: warm up, then ride as hard as you can sustain for 20 minutes. Your FTP is approximately 95% of your 20-minute average power. Many apps like Zwift and TrainingPeaks can estimate FTP from your ride data.
Yes, alternatives exist. hrTSS uses heart rate data, rTSS (running TSS) uses pace and heart rate, and sRPE (session RPE) multiplies perceived exertion by duration. However, power-based TSS is the most accurate.
Beginners should start with 200-300 weekly TSS and increase by no more than 10% per week. Listen to your body and prioritize consistency over high volume. After 6-12 months, you can gradually increase to 400-500 TSS/week.
Differences usually come from varying FTP values. Ensure your FTP is up-to-date in all devices. Also, some platforms use slightly different NP algorithms. For consistency, stick to one platform for TSS tracking.
Power-based TSS doesn't directly account for altitude. However, riding at altitude is harder (lower power output for the same perceived effort), which naturally results in lower TSS. Some coaches apply an altitude correction factor of 2-5% per 1000m elevation.
For serious training, yes. Tracking TSS for all cycling workouts helps you understand your training load over time. For casual riders, tracking weekly totals is sufficient to avoid overtraining.
Additional Resources
For more health and fitness calculators, explore our complete collection at Calculator Cloud. We offer calculators for BMI, TDEE, heart rate zones, and many more training metrics to help optimize your performance.