Broken 1000m Time Trial: 10x100m Build to CSS Pace

Session Overview

A progressive pool session where you build pace across 10 x 100m intervals, finishing at or faster than CSS. Perfect for intermediate swimmers looking to sharpen their race-day pace awareness and test their 1000m fitness.

What You’ll Need

• 25m or 50m swimming pool with a visible pace clock
• Waterproof watch or stopwatch
• Swim goggles and cap
• Optional: pull buoy for cool-down

Warm-Up (10 minutes)

Swim 400m easy at Zone 1 pace, alternating 100m freestyle with 100m backstroke. Focus on long strokes and relaxed breathing. Finish with 2 x 25m building from easy to 85% effort to prime your fast-twitch fibres before the main set.

Main Set

10 x 100m on a rolling 2:30 send-off (adjust to 2:15 for faster swimmers, 2:45 for those new to structured sets). Build pace progressively across the 10 reps as follows:

• Reps 1–3: 5–8 seconds per 100m slower than your CSS pace — feel comfortable
• Reps 4–6: 2–4 seconds per 100m slower than CSS — steady effort, controlled breathing
• Reps 7–9: Exactly at CSS pace — this is the target zone, maintain technique
• Rep 10: All out — aim to match or beat CSS pace even under fatigue

Cool-Down (5 minutes)

200m easy with a pull buoy or backstroke to flush lactic acid from the shoulders and arms. Focus on slow, deliberate rotation rather than distance.

Coaching Notes

• CSS (Critical Swim Speed) is calculated from a 400m and 200m time trial: divide (400m time minus 200m time) by 200 to get your pace per metre
• Watch your stroke rate in reps 7–10 — don’t let it collapse when tired; shorten your stroke before you windmill
• To scale down: reduce to 8 x 100m with a 3-minute send-off
• To scale up: after the 10 x 100m, add 5 x 50m all-out with 1 minute rest each
• Target RPE: 5–6 for reps 1–3, building steadily to 9 on rep 10