TSS (Training Stress Score) takes every ride you do and distills it into a single number that captures both intensity and duration. A 1-hour ride at FTP produces a TSS of 100. Everything else is relative to that.
Your cycling computer or app calculates it automatically. You don't need to think about the formula. You need to think about what the numbers mean.
What TSS numbers feel like
- Under 150: Low. You'll be recovered by tomorrow.
- 150-300: Moderate. Some residual fatigue the next day.
- 300-450: High. You'll feel it for 2+ days. Think long group rides or hard race simulations.
- Over 450: Stage-race territory. Plan on extended recovery.
Weekly targets by level
- Beginner: 300-400 TSS/week
- Intermediate: 400-600 TSS/week
- Advanced: 600-900 TSS/week
- Pro: 800-1200+
These assume the stress is distributed properly across the week. Cramming 600 TSS into 3 days is nothing like spreading it across 6.
How to use TSS for planning
Progressive overload. Increase weekly TSS by 5-10% during a build block. Bigger jumps are asking for trouble.
Recovery weeks. Every 3-4 weeks, drop TSS by 40-50%. A rider averaging 600/week should drop to 300-360 during recovery weeks.
Taper. Before a key event, reduce TSS by 40-60% over 1-2 weeks while keeping short, sharp efforts. More on this in the tapering guide.
TSS without a power meter
If you don't have a power meter, TSS can be estimated from heart rate (hrTSS) or perceived effort (RPE). Heart rate is less precise than power but still useful. RPE is rougher but better than nothing.
Nivvy calculates training stress from whatever data source you have. Power gets priority, then heart rate, then RPE. No power meter required.
The bigger picture: CTL, ATL, TSB
TSS feeds three long-term metrics:
- CTL (Chronic Training Load): 42-day rolling average of daily TSS. Your "fitness."
- ATL (Acute Training Load): 7-day rolling average. Your "fatigue."
- TSB (Training Stress Balance): CTL minus ATL. Negative = fatigued. Positive = fresh. Optimal race readiness is TSB of +15 to +25.
These aren't perfect. But they're the best quantitative tools we have for managing training load over weeks and months. And they all start with TSS.