Estimated Running Power

FitOps estimates running power from pace streams using a calibrated proxy model. The estimate is computed once on the first activity get or dashboard detail view, then persisted to the DB so subsequent reads are instant.

Formula

Power (W) = Cdisplay × mass_kg × velocity (m/s)

Where Cdisplay = 1.0 J/(kg·m) is a calibrated displayed-power constant chosen to keep values in a realistic Garmin/Stryd-like running power range. Grade and wind effects are captured implicitly when the true pace stream is available.

Pace stream priority

FitOps selects the best available pace source:

1. true_pace — grade- and wind-adjusted pace (most accurate)
2. gap_pace — grade-adjusted pace from Strava
3. velocity_smooth — raw GPS speed (fallback)

The source field in the power output block indicates which stream was used. If power was first estimated before weather was available, later write paths that have weather and stream data, such as activity stamping, upgrade the estimate to true_pace instead of keeping the earlier gap_pace fallback.

Normalized Power (NP)

NP is computed as the fourth-root mean of a 30-second rolling window of P^4. It better represents the physiological cost of variable-intensity efforts than average power.

NP = ( mean( rolling_30s( P^4 ) ) )^(1/4)

Calorie estimation

kcal = Σ (metabolic_power × Δt) / 4184

Displayed watts are calibrated for user-facing running power. Calorie estimation uses a higher metabolic-cost model internally, so est_kcal remains closer to actual running energy expenditure than a direct conversion from the displayed watts would be.

Output fields

Field	Description
avg_w	Average estimated power (W), rounded
max_w	Peak estimated power (W), rounded
np_w	Normalized power (W), rounded
est_kcal	Mechanical energy estimate (kcal)
source	Pace stream used: true_pace, gap_pace, or velocity_smooth

Example

"power": {
  "avg_w": 248,
  "max_w": 412,
  "np_w": 255,
  "est_kcal": 830,
  "source": "true_pace"
}

Limitations

• Requires body weight configured in athlete settings (fitops athlete set weight_kg <value>).
• Calibrated proxy, not device-native power. It is intended to land in realistic consumer running-power ranges, not to reproduce Garmin or Stryd exactly.
• No wind correction unless weather was fetched for the activity.
• Not comparable to cycling power (different efficiency and Cr constants).