Threshold Swim: CSS Pace Sets for Triathlon Speed

Session Overview

This 60-minute threshold swim targets your Critical Swim Speed — the pace you can sustain for extended efforts without accumulating excessive lactate. CSS training is the single most effective method for improving open water race pace over a training block, and this session delivers a structured, measurable workout to build that engine.

What You’ll Need

• Access to a 25m or 50m pool
• Swim watch or poolside pace clock
• Pull buoy (optional, for warm-up variety)
• Fins (optional, warm-up drills only)

Warm-Up (10 minutes)

300m easy freestyle focusing on long, relaxed strokes and bilateral breathing every 3 strokes. Follow with 4 x 50m on 15 seconds rest — choose a catch-up drill, fingertip drag, or single-arm freestyle to engage your catch and establish a quality pull pattern before the hard work starts.

Main Set

Your CSS pace is the pace you could sustain for 15–20 continuous minutes. If you don’t have a tested CSS figure, use your comfortable Olympic-distance race pace or target RPE 7–8/10. Consistency across all reps is the goal — negative splitting is fine, but fading reps mean you started too fast.

• 6 x 200m at CSS pace — 30 seconds rest between reps; hold the same split for all six
• 4 x 100m at CSS pace — 20 seconds rest; maintain stroke length and breathing rhythm
• 4 x 50m at 3–5 seconds per 100m faster than CSS — 15 seconds rest; these build speed endurance and push the upper end of your threshold

Cool-Down (5 minutes)

200m of easy backstroke or very relaxed freestyle. Let your heart rate fall naturally and breathe under control. Finish with 30 seconds of shoulder circles and a brief lat stretch in the water before exiting.

Coaching Notes

• Track your splits on every rep — if you can’t hold even pace across the 200m block, you started too fast; the data tells the truth
• Don’t spike your stroke rate to hold pace — focus on increasing distance per stroke rather than faster turnover; 16–20 strokes per 25m is the target
• Scaling down: reduce to 4 x 200m, 3 x 100m, 3 x 50m keeping the same rest intervals
• Scaling up: increase the 200m block to 8 reps, or reduce rest to 20 seconds on the 200s