Broken 1200m CSS Time Trial Pool Session

Session Overview

A broken 1200m time trial splits your CSS (Critical Swim Speed) test into manageable chunks with short rest, rather than one continuous swim. You’ll hold a harder average pace than a continuous time trial because the brief rests let you recover just enough to keep form together, giving you a more accurate CSS pace to train off going forward.

What You’ll Need

  • Pace clock or watch with lap timing
  • Pool with clearly marked 25m or 50m lengths
  • Swim log to record split times (optional but recommended)

Warm-Up (10 minutes)

400m easy freestyle building from very easy to moderate effort, followed by 4 x 50m at a steady pace with 15 seconds rest, focusing on a clean catch and consistent tempo.

Main Set

Swim 1200m broken into 6 x 200m at maximum sustainable effort, taking only 10 seconds rest between each 200m. The short rest is deliberate — long enough to catch your breath but not long enough to fully recover, so your average pace across all six reps closely approximates a genuine 1200m time trial effort.

  • 6 x 200m, hold the fastest average pace you can sustain across all six, 10 seconds rest between reps
  • Record every split — your CSS pace is calculated from total time and total distance across the set
  • Aim for even pacing rather than a fast start that fades by rep 4

Cool-Down (10 minutes)

300m easy swim mixing freestyle and backstroke, followed by gentle stretching for shoulders and lats poolside.

Coaching Notes

  • To calculate CSS from this set: CSS pace (per 100m) = total time for 1200m ÷ 12.
  • If your splits vary by more than 3–4 seconds per 200m across the set, you started too fast — dial back the first two reps next time.
  • Retest every 4–6 weeks during a training block to keep your CSS pace current as fitness improves.
  • This is a genuinely hard session — schedule it when you’re fresh, not after a heavy bike or run day.

Training at your own risk. The information provided is for general guidance only and is not a substitute for professional medical advice. Please consult a doctor before starting any new exercise programme, especially if you have any pre-existing health conditions.