Pool swims

A pool swim is told in its own words: the pool, the lengths swum, the rests at the wall, and the repeats. isPoolSwim() narrows an activity to a PoolSwim, which has them.

import { readFileSync } from 'node:fs';
import { readActivity } from '@pond-ts/fit/files';

const swim = readActivity(readFileSync('pool-swim.fit'));
console.log(swim.sport, swim.environment, swim.isPoolSwim());

if (swim.isPoolSwim()) {
  console.log(swim.pool?.course, swim.pool?.length.meters);
  console.log(
    swim.lengths.length,
    'lengths,',
    swim.segments.length - swim.lengths.length,
    'rests',
  );
  console.log(swim.repeats.length, 'repeats');
}

swim pool true
25m 25
52 lengths, 11 rests
12 repeats

The watch tells a swim apart from its rests by its length records, so moving time on a pool swim is the time spent in lengths. See Clocks.

Lengths and rests

segments is the swim in order: each a LengthSection or a RestSection. A rest is a rest at the wall, not a length with nothing in it.

if (swim.isPoolSwim()) {
  for (const seg of swim.segments.slice(10, 16)) {
    if (seg.kind === 'length')
      console.log(
        seg.label.padEnd(10),
        seg.stats().time.elapsed?.format(),
        seg.stroke,
        seg.strokeCount,
      );
    else console.log('Rest'.padEnd(10), seg.duration.format());
  }
}

Length 11  0:29 freestyle 21
Length 12  0:30 freestyle 22
Rest       0:40
Length 13  0:22 freestyle 15
Length 14  0:23 freestyle 16
Length 15  0:24 freestyle 16

A length's stroke is what the watch recognised ('freestyle', 'drill', …) and strokeCount is what it counted, as it counted it: a Garmin watch counts cycles of the arm wearing it, not every arm pull. A drill length (drill === true) has no swimming strokes.

Repeats and recovery

The repeats come from the recorded laps: each lap that covered distance is a repeat, with the lengths inside it, and the no-distance lap after it is its recoveryAfter.

if (swim.isPoolSwim()) {
  for (const rep of swim.repeats) {
    const s = rep.stats();
    const per100 = s.pace.average ? s.pace.average.secondsPerKm / 10 : null;
    console.log(
      rep.label.padEnd(10),
      `${rep.lengths.length} × ${swim.pool?.course}`.padEnd(9),
      s.time.elapsed?.format().padStart(5),
      per100 !== null ? `${per100.toFixed(1)} s/100m` : '',
      rep.recoveryAfter
        ? `then ${rep.recoveryAfter.duration.format()} rest`
        : '',
    );
  }
}

Repeat 1   12 × 25m   5:26 108.7 s/100m then 0:40 rest
Repeat 2   4 × 25m    1:33 93.0 s/100m then 0:20 rest
Repeat 3   4 × 25m    1:33 93.0 s/100m then 0:20 rest
Repeat 4   4 × 25m    1:35 95.0 s/100m then 0:20 rest
Repeat 5   4 × 25m    1:33 93.0 s/100m then 0:20 rest
Repeat 6   4 × 25m    1:35 95.0 s/100m then 0:20 rest
Repeat 7   4 × 25m    1:35 95.0 s/100m then 0:20 rest
Repeat 8   2 × 25m    1:09 138.0 s/100m then 0:15 rest
Repeat 9   2 × 25m    1:11 142.0 s/100m then 0:15 rest
Repeat 10  2 × 25m    1:11 142.0 s/100m then 0:15 rest
Repeat 11  2 × 25m    1:08 136.0 s/100m then 0:15 rest
Repeat 12  8 × 25m    3:52 116.0 s/100m

fit formats pace per kilometre or per mile only, so the example works out seconds per 100 m from secondsPerKm.

The six 100s are repeats 2 to 7; a group of them adds up the 100s alone, without the rests:

if (swim.isPoolSwim()) {
  const hundreds = swim.repeats.filter((r) => r.lengths.length === 4);
  const s = hundreds.stats();
  console.log(hundreds.length, s.distance?.meters, s.time.elapsed?.format());
}

6 600 9:24

Open water

An open water swim has environment === 'open-water' and isn't a PoolSwim. Its distance comes from the watch's own count when the file has it, because GPS fixes in the water are sparse and zigzag; its line is cleaned up for the map.