xPower LAP & SESSION

xPowerLap — Dr. Skiba xPower per Lap and Session This data field implements Dr. Philip Skiba's xPower (the physiological counterpart to Coggan's Normalized Power). xPower is the 4th-root of the mean of the 4th powers of an exponentially weighted moving average (EWMA) of power with a 25 s time constant. It weights high-power efforts exponentially to reflect metabolic cost (Skiba, 2006-2008). Lap handling: xPowerLap maintains two independent states. Total (session) accumulates from activity start and is never reset. Lap state (EWMA_lap, EWMA_4_lap, seg_lap, xPower_lap) is reset on every lap (onTimerLap, manual or AutoLap). The frozen xPower_lap of the finished lap is published to the FIT LAP field before the reset, so the Laps table always gets the correct value. This gives a true per-interval xPower isolated to the current lap, while still showing the whole-ride xPower for comparison. FIT file (when "Save metrics to .fit file?" is enabled): - id0 RECORD FLOAT "xPower" — xPower_total sampled every second → continuous chart in Garmin Connect - id1 SESSION FLOAT "xPowerSession" — final xPower_total → Activity Summary - id2 LAP FLOAT "xPowerLap" — xPower_lap frozen per lap → Laps table Requirements: - Power meter required. Recording interval 1 s recommended (works with any interval, dt-exact). - Autopause can stay enabled (timerTime based dt). References: - Skiba PF. Calculation of Power Output at Different Effort Durations. 2006. - Skiba PF, Clarke D, Vanhatalo A, Jones AM. Validation of a Novel Intermittent W′ Model... 2014 (EWMA/xPower basis). - Coggan AW. Normalized Power concept (xPower is Skiba's exponential variant).