Session TSS from power or pace
Hunter Allen and Andrew Coggan defined Training Stress Score as TSS = (seconds × NP × IF) / (FTP × 3600) × 100, with IF = NP / FTP. Because NP / FTP appears twice, it simplifies to hours × IF² × 100. Intensity counts squared, so 30 minutes at threshold (50 TSS) costs as much as about 70 minutes at IF 0.65.
For running, TrainingPeaks' rTSS uses the same form with normalized graded pace against your threshold pace, the fastest pace you could hold for about an hour. Pace is time per kilometre, so the ratio flips: IF = threshold pace / normalized graded pace. A 5:00/km run with a 4:00/km threshold is IF 0.8.
We do not calculate heart-rate TSS. TrainingPeaks derives hrTSS from time in heart-rate zones and does not publish a closed formula, so any version we built would be a guess.
Fitness, fatigue and form
The Performance Manager comes from Eric Banister's impulse-response model, which treats every session as producing both a fitness effect and a larger but shorter-lived fatigue effect. Coggan's version tracks chronic training load (CTL, 42-day time constant) as fitness and acute training load (ATL, 7-day time constant) as fatigue.
Each day, CTL moves toward that day's TSS by a factor of 1 − e^(−1/42), about 2.4 %, and ATL by 1 − e^(−1/7), about 13.3 %. Training stress balance (TSB = CTL − ATL) is your form. It goes negative in hard blocks and positive when you back off.
What the numbers mean
Ramp rate is the change in CTL over a week. Joe Friel writes that an increase of about 5 to 8 CTL points per week is right for most athletes, and that elites who ramp above 10 should not hold it for more than a week before recovering.
TrainingPeaks' coach guide puts productive training at a TSB of −10 to −30, flags anything below −30 as extreme strain, and gives +15 to +25 as the usual range for a peak race. Science to Sport's Mike Posthumus notes that some athletes race best at +10 to +20 and others at −5 to +5, so treat these as a starting point.
Load is feedback, not a target. Build the plan from sessions first, then use this projection to check the plan does not ramp too fast. Our guide to managing training load covers why.
The taper option
Bosquet and colleagues' 2007 meta-analysis found the best tapers last about two weeks and cut training volume by 41 to 60 % while keeping intensity. With intensity held, TSS falls in step with volume, so the taper option keeps 50 % of your weekly load for the final one or two weeks. Watch TSB climb toward race form while CTL dips only a few points.
How it works
- 1Score a session. Pick power or pace, then enter duration, normalized power or normalized graded pace, and your FTP or threshold pace.
- 2Enter a typical week. Type the TSS of each day in a normal training week. Rest days are 0.
- 3Set your starting fitness. Enter your current CTL, or 0 if you do not track it. The projection assumes fatigue starts at the same level.
- 4Choose the block. Pick how many weeks you repeat that week and whether to taper for the last one or two.
- 5Read the chart and table. Check the weekly ramp against 5 to 8 points and where TSB lands on race week.
Frequently asked questions
What is a good TSS for a workout?
TSS depends on duration and intensity together. An hour at threshold is 100, a one-hour easy ride at IF 0.65 is about 42, and a two-hour endurance ride at IF 0.7 is about 98. What matters is how daily TSS adds up over weeks.
What is a good CTL?
There is no universal number. Mike Posthumus gives a range from about 70 TSS per day for competitive age-groupers to around 140 for pro tour cyclists. Compare your CTL with your own history and your results, not with other athletes.
How fast can I increase CTL?
Joe Friel recommends about 5 to 8 CTL points per week for most athletes. Some elites handle 10 or more for short periods, but Friel advises no more than about a week at that rate before recovery.
What TSB should I have on race day?
TrainingPeaks cites +15 to +25 for a peak performance. It is individual: some athletes race best at +10 to +20 and some at −5 to +5. Use your own past races to find your number.
Why is TSB negative most of the time?
Because ATL reacts about six times faster than CTL, any training block pushes fatigue above fitness. A TSB of −10 to −30 is the normal productive range. It only turns positive when you ease off.
Sources
- Allen, H. & Coggan, A. Training and Racing with a Power Meter, 2nd ed. VeloPress, 2010.
- TrainingPeaks. Running Training Stress Score (rTSS) explained.
- Calvert, T., Banister, E. et al. (1976). A systems model of the effects of training on physical performance. IEEE Transactions on Systems, Man, and Cybernetics 6(2): 94-102.
- Friel, J. The CTL ramp rate.
- TrainingPeaks. A coach's guide to ATL, CTL and TSB.
- Posthumus, M. Monitoring cyclist training load. Science to Sport, 2025.
- Bosquet, L. et al. (2007). Effects of tapering on performance: a meta-analysis. Medicine & Science in Sports & Exercise 39(8): 1358-1365.
Last updated 6 September 2026.