OptionalavgOptionalavgOptionalavgOptionalcaloriesEnergy, kcal.
Wall-clock for the lap (total_elapsed_time).
Optionalelevation1-based lap number in recorded order.
OptionalmaxOptionalmaxOptionalmaxThe lap's moving time as the reader estimates it. FIT fills it from
total_timer_time (else elapsed), TCX from elapsed, so today it is
timer time under another name; timerSeconds is the file's own
timer, and the clocks work will untangle the two.
Cumulative distance at the lap's start (sum of prior laps' distance), metres — the lap's [start, start+distance] range into the activity, for chart bands and map-section highlighting.
OptionalstartISO 8601, UTC — when the lap began. Optional: absent (not '') when the
source recorded no valid start time, so consumers must null-check rather
than Date.parse('') → NaN.
OptionaltimerTime the recording timer ran over the lap (FIT total_timer_time).
Absent when the file doesn't record it — never filled from elapsed.
OptionaltotalMechanical work over the lap, kJ (FIT total_work is joules).
A recorded lap — a segment the device marked (auto-lap by distance/time, or a button press), as opposed to the evenly-spaced splits this library computes. Recorded laps are the rider's own structure (intervals, climbs, rest stops), so they're carried through as first-class evidence. SI throughout; optional fields are present only when the source recorded them.