Distance · 12 weeks · Free

The 200–1,500m Endurance Engine

A real 12-week plan to build the aerobic engine that turns a gasping 50m into an easy 1,500m. Three phases, CSS-anchored, four sessions a week. No subscription, no tier, no upsell — just the plan.

12 weeks 3 swim + 1 dryland / wk Needs: pool access, watch Level: novice to club

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How this plan works

The plan is built around your Critical Swim Speed (CSS) — your sustainable threshold pace per 100m. Find yours in 30 seconds with the Swimzy CSS calculator before starting. Every set in this plan is anchored to that number.

Three 4-week phases:

Phase 1 — Aerobic Base (weeks 1–4): high volume, low intensity. Stroke economy. Long, easy sets.
Phase 2 — Threshold Build (weeks 5–8): CSS-paced volume. The bread and butter of distance.
Phase 3 — Race Endurance (weeks 9–12): broken sets at CSS−5/100. Race-pace tolerance, sharpened.

Retest your CSS at the start of week 5 and week 9 and re-anchor the sets to your new number. The plan tightens automatically as you get faster.

Why CSS-anchored

Critical Swim Speed (Ginn, 1993) is the pace at which aerobic capacity is maximised without crossing into anaerobic breakdown. Sets paced at CSS develop the engine you actually use for 400m, 800m, 1,500m, and 5K open water.

Mauger et al. (2009, J. Sports Sciences) showed that pacing-anchored training reduces energy expenditure at submaximal speeds — meaning the same pace costs you less effort after this kind of block.

Mauger et al., 2009 (PubMed)

Phase 1 — Aerobic Base (weeks 1–4)

Goal

Build volume tolerance and stroke economy

Long, easy continuous swimming. No watches in race-pace mode. The goal is to be able to hold a clean stroke at CSS + 10/100m for 25–35 minutes straight by the end of week 4.

Weekly template

Day	Session
Mon	Easy aerobic + drills WU 300 easy + 200 drill choice MAIN: 4 × 400 at CSS + 10/100, 30s rest CD 200 easy. ~2,200m total
Wed	Pull-buoy aerobic WU 400 easy MAIN: 2,000m straight on pull buoy at CSS + 15/100, sighting every 50 CD 200 easy. ~2,600m total
Fri	Long technique swim WU 400 easy MAIN: 8 × 200 at CSS + 8/100 with 20s rest. Every other 200, count strokes per 50. CD 200 easy. ~2,200m total
Sat	Dryland — Pulling-Priority 45 min: 3 × 8 lat pulldown, 3 × 10/side single-arm row, 3 × 10 hip thrust. Slow eccentric on every rep.

Coaching cues

If you can't hold the pace cleanly, the pace is too fast. Slow down — base phase only.
Stroke count per 50 should stay within ±1 stroke across the whole main set. Decay = fatigue creeping.
Breathe every 3 strokes minimum. Build bilateral comfort here so it's free at race pace later.

Phase 1 weekly load: ~6,500–7,000m swimming + 1 dryland. Total ~3.5 hours.

Phase 2 — Threshold Build (weeks 5–8)

Goal

Raise CSS by 3–5 seconds per 100m

CSS pace becomes the centre of every main set. Retest your CSS at the start of week 5 with a 400m + 200m time trial and use the new number. Repeat at week 7.

Weekly template

Day	Session
Mon	10×100 on CSS WU 400 + 4 × 50 build MAIN: 10 × 100 on CSS pace, 15s rest. Hold the pace; if you slip, take an extra 5s and finish the set. CD 200 easy. ~1,900m total
Wed	Broken 1,500 WU 400 MAIN: 3 × 500 at CSS + 2/100, 30s rest. (Equivalent to a 1,500 with three short breaks.) CD 200 easy. ~2,100m total
Fri	Mixed-pace ladder WU 400 MAIN: 200 / 300 / 400 / 300 / 200 — all at CSS pace, 30s rest each. Don't fall off pace on the 400. CD 200 easy. ~2,000m total
Sat	Dryland Same 45-min Pulling-Priority block as Phase 1. Add 5kg to deadlift, hold rep targets.

Coaching cues

If you finish all 10 × 100 on send-off cleanly, your CSS has improved — retest sooner than week 7.
The 30s rest is the rest. No bonus rest, no skipped reps. Earn the recovery in the next phase.
If you cramp or stroke collapses past rep 8 of the 10×100, drop send-off by 3s for one week, then retry.

Phase 2 weekly load: ~6,000m swimming + 1 dryland. Total ~3 hours. The pace is harder; the volume is similar.

Phase 3 — Race Endurance (weeks 9–12)

Goal

Race-pace tolerance + taper

Retest CSS at week 9. Then move to broken work at CSS − 5/100 — meaningfully faster than threshold. Volume drops; pace rises. Week 12 is taper week.

Weekly template (weeks 9–11)

Day	Session
Mon	Broken race WU 400 + 4 × 50 build MAIN: 16 × 50 at CSS − 5/100, 15s rest. Then 4 × 100 at CSS pace as a finisher. CD 200 easy. ~1,800m total
Wed	Pace lock WU 400 MAIN: 6 × 200 — odd at CSS, even at CSS − 5/100. 30s rest. Alternate. Train your gear changes. CD 200 easy. ~1,800m total
Fri	Race rehearsal WU 400 + 4 × 50 race-pace dives MAIN: 1 × 800 at CSS − 3/100, even split. This is the race rehearsal. CD 200 easy. ~1,800m total
Sat	Dryland (reduced) 30 min: 2 × 6 lat pulldown, 2 × 8/side row, 2 × 8 hip thrust. Maintain, don't push PRs.

Week 12 — Taper

Cut volume by 50%. Keep intensity. Two short sharp swims:

Mon: WU 400 + 6 × 50 at CSS − 5, 30s rest + 4 × 100 at CSS, 30s rest + CD 200. ~1,400m.
Thu: WU 300 + 3 × 100 race-pace dives, full recovery. ~700m.
Race day: empty the tank.

Coaching cues

Even splits beat negative splits beat positive splits. Train the discipline.
The taper week feels too easy. That's the point. Trust it.
If you've held the plan, your CSS at week 12 should be 6–10 seconds per 100m faster than week 1. That's a transformed engine.

Phase 3 weekly load: ~5,400m / wk in 9–11; ~2,100m in taper week. Total ~2.5 hours per week.

If you only do one thing

Test your CSS today. Then do 1 session per week of 10 × 100 on CSS pace with 15 seconds rest. That single weekly set, held for 12 weeks, will rebuild your distance engine more than any other change. Everything else here is amplification.

Coach's note

This plan assumes pool access for 3 sessions a week. If you only have access to 2, drop Wednesday's session and keep Monday + Friday. The dryland is non-negotiable — that's where the posterior chain that holds your hips up under fatigue gets built.