What the FIT parser computes on an Activity

What gets parsed

When you upload a workout file (FIT, TCX, or GPX), the Hub extracts an Activity row plus per-lap ActivityLap rows. The metrics below are what the parser captures and stores; if a field is empty on your Activity, the source file did not contain it.

Universal fields

• Sport (swim, bike, run, strength, other) and sub_sport (pool / open_water / indoor_cycling / outdoor_cycling / indoor_run / outdoor_run).
• Date and start time.
• Duration in seconds.
• Distance in metres.
• Title (auto from device if not set).
• Source format (fit / tcx / gpx) and device name.

Heart rate

• Average HR and max HR.
• Plus optional HRV (RMSSD and SDRR) from devices that measure it.

Bike-specific

• Average / max / normalized power.
• Intensity Ratio (IF) = AdjP / FTP.
• Average cadence.
• Average / max speed.
• Total calories.
• Avg temperature.
• Elevation gain / loss.
• MMP curve (Mean Maximal Power across all durations), stored as JSON.
• Power zone seconds (time in each Yousuli power zone), stored as JSON. See Glossary: zones.
• Pedal metrics (if dual-side power meter): L/R balance, torque effectiveness, pedal smoothness, power phase data.
• Total work in kJ.
• Electronic shifting data: gear changes, gear time distribution, average front / rear gear and gear ratio (if Di2, eTap, etc.).

Run-specific

• Average / max cadence (steps per minute).
• Stryd or Garmin running dynamics when present:
• Form power and air power (Stryd).
• Leg spring stiffness (Stryd).
• Ground contact time, vertical oscillation, vertical ratio, stance time, stance time balance, vertical oscillation balance.
• Stride length.
• Impact loading rate, leg spring stiffness balance.
• Impact Gs.
• Stryd environment data (temperature, humidity).
• Training effect (aerobic + anaerobic) when Garmin provides it.

Swim-specific

• Pool length (m).
• Average stroke rate (strokes per minute).
• Average distance per stroke (DPS) in metres.
• SWOLF (swim golf score, stroke count + duration per length).
• Total strokes.

Advanced physiology (when sensors attached)

• SmO2 (muscle oxygen) and THb (total hemoglobin).
• VO2 (continuous, from a metabolic device).
• Breathing rate and tidal volume.
• FeO2 (expired oxygen fraction).
• Core temperature and skin temperature.

GPS

• Has GPS flag.
• GPS track (JSON) and bounding box for map rendering.

Training load (auto-computed)

• Load with method selected by priority: power → speed/pace → HR. Plus a tss_override field for manual coach override. See Load computation and override.
• Intensity Ratio (AdjP / FTP).

Data quality

• Quality flags (JSON list of auto-detected issues).
• Needs review flag for activities with anomalies. See Activity quality flags.

Per-lap data

Every lap from the FIT file becomes an ActivityLap row with: duration, distance, average and max power, normalised power, average and max HR, average cadence, average and max speed.