CSS Ladder Swim: 400/300/200/100 at Critical Swim Speed

Session Overview

This CSS ladder swim uses your critical swim speed (CSS) pace to build speed and endurance simultaneously. Perfect for intermediate triathletes looking to sharpen race-pace swimming, this 45-minute session challenges you to hold threshold effort across descending distances without collapsing your form.

What You’ll Need

• Pool access (25m or 50m)
• Swim watch or poolside clock
• Goggles and swim cap
• Pace card or CSS pace noted on your hand (optional)

Warm-Up (10 minutes)

Swim 400m easy at RPE 3-4, broken into 200m continuous then 4x50m with 10 seconds rest. Focus on long strokes and relaxed breathing. Finish with 2x25m catch-up drill to activate your pull before the main set.

Main Set

Your CSS pace is calculated as: (400m TT time minus 200m TT time) divided by 2 = pace per 100m. Complete the following ladder twice through with 90 seconds rest between each rep and 3 minutes rest between complete sets:

• 400m at CSS pace — hold your exact target pace throughout
• 90 seconds rest
• 300m at CSS pace — manageable but focused effort
• 90 seconds rest
• 200m at CSS pace — stroke quickens slightly as you shorten
• 90 seconds rest
• 100m at CSS pace — stay relaxed, resist the urge to sprint
• 3 minutes rest, then repeat the full ladder once more

Cool-Down (5 minutes)

Easy 200m at recovery pace (RPE 2-3), alternating backstroke and freestyle. Focus on long, relaxed strokes and slow your breathing. Finish with a gentle 50m kick-only to flush the legs.

Coaching Notes

• If you do not know your CSS pace, start at 70-75% effort and refine after a time trial
• The most common mistake is going out too fast on the 400m — pace discipline is the whole point
• Easier: shorten to one full ladder or increase rest to 2 minutes between reps
• Harder: reduce rest to 60 seconds or add a third run-through of the ladder
• Target RPE 6-7 throughout — controlled threshold, not maximal effort