PSS — Power Stress Score
PSS combines timer duration with weighted power relative to the applicable FTP.
Formula and inputs
PI = Weighted Power / effective FTP
PSS = (timer seconds / 3600) × PI² × 100Weighted 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 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
PSS is threshold-relative: changing the applicable FTP changes the score even for unchanged watts. It is not interchangeable with TRIMP. PSS appears in activity, volume, planning and progress contexts, but does not feed EffortSignal’s CTL/ATL history. The Readiness workload component has its own documented use of PSS.
Sources and implementation scope
Coggan, power-based training metrics provides background, not a specification of every EffortSignal rule. The formulas, windows, quality gates and examples above describe EffortSignal 0.1.13, checked September 10, 2026. Product-specific thresholds and rounding should not be attributed to the background source.
Content checked September 10, 2026 · EffortSignal release 0.1.13