# PSS — Power Stress Score

Canonical HTML: https://effortsignal.com/learn/pss/

Last content update: 2026-10-04

Published: 2026-09-11

Author: [EffortSignal Editorial Team](https://effortsignal.com/editorial-standards/)

PSS combines timer duration with weighted power relative to the applicable FTP.

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Familiar with TSS®? [Why EffortSignal calls it PSS](/learn/power-metric-names/) explains the registered names, identical core formulas and what to check when comparing values.

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## What TSS and PSS tell you

Training Stress Score® (TSS®) combines workout duration and intensity relative to your threshold into a load score. EffortSignal calls its power-based score PSS. For cycling, the same duration, weighted power and FTP give the same PSS and power-based TSS. A heart-rate-based or pace-based score is not automatically equivalent.

Use the score to compare the recorded load of your own sessions and weeks. It helps answer whether a bigger week came from more time, harder riding, or both. It does not measure fitness gained, how recovered you feel, or how good the workout was.

## How to read the number

One hour at threshold intensity is the reference of 100 points, not a daily target. With FTP 250 W, an hour at weighted power 200 W gives 64 PSS; two hours at the same intensity give 128 PSS. An hour at weighted power 250 W gives 100 PSS. These calculation examples show why hours alone cannot describe load.

Equal scores can come from different sessions. Two hours at PI 0.5 and half an hour at PI 1 both give 50 PSS, but their duration and intensity differ. Keep the session purpose and intensity distribution beside the total. Compare like sports and check the applicable FTP before interpreting a change.

## Read weeks, not just totals

In [Training Volume](/features/training-volume/), choose PSS and compare complete weeks in the same sport. Switch to Duration to see whether training time changed, then inspect the sessions in [Training Calendar](/features/training-calendar/). Four weeks of 100, 100, 100 and 100 PSS have the same total as 0, 0, 200 and 200 PSS; the second pattern concentrates the work. Consistency concerns the pattern across weeks as well as the sum.

When reviewing a build-up, separate added time from added intensity and compare the change with your recent routine, session results and [check-ins](/features/check-ins-notes/). A lighter week or a return after a break needs that context. The usual range describes your history; its upper edge is not a target or a safe progression limit. Neither a weekly score nor a fixed percentage increase can decide the next week's training for you.

## Formula and inputs

```text
PI = Weighted Power / effective FTP
PSS = (timer seconds / 3600) × PI² × 100
```

Weighted Power and FTP are in watts; PSS is a score. One hour at PI = 1 yields 100 PSS. The activity's effective threshold profile supplies cycling FTP, an explicitly configured indoor FTP for an indoor ride, or running threshold power for running. A run does not inherit cycling FTP. A threshold whose effective date is later than the activity is not automatically valid for that earlier recording.

## Verified example

A one-hour constant-power recording at 200 W with effective FTP 250 W has Weighted Power 200 W, PI 0.8 and PSS 64. A 30-minute recording with the same output and threshold has PSS 32.

## Pauses, zeros and missing data

The [Weighted Power](/learn/weighted-power/) calculation uses complete 30-second windows on compressed timer time and needs at least 80% power coverage. Real zero watts count as coasting; absent power remains missing. The positive recorded timer/moving duration supplies the PSS duration, with projected timer duration as fallback. Unsupported sport, unavailable weighted power or no valid positive applicable FTP prevents PSS. A short recording can carry lower confidence.

## Meaning and recalculation

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PSS is threshold-relative: changing the applicable FTP changes the score even for unchanged watts. It is not interchangeable with [TRIMP](/learn/trimp/). PSS appears in activity, volume, planning and progress contexts, but does not feed EffortSignal's [CTL/ATL history](/learn/training-load/) or the [Readiness workload component](/learn/readiness/#workload), which both use TRIMP.

## Sources and implementation scope

[Coggan, power-based training metrics](https://www.trainingpeaks.com/learn/articles/normalized-power-intensity-factor-training-stress/) explains the research background. The formulas, windows, quality gates and examples above describe EffortSignal 0.1.13, checked September 10, 2026. Thresholds and rounding are EffortSignal rules.