Ascending Distance Pool Endurance Swim: 100s to 400s Progression Set

Session Overview

This session builds aerobic endurance by progressively increasing repetition distance — from 100m blocks up to a 400m closing rep. The ascending format trains you to hold pace as effort accumulates, a key skill for triathlon swimming where the second half of the swim is always harder than the first.

What You’ll Need

• Access to a 25m or 50m pool
• Swim watch or pace clock
• Pull buoy (optional for the 300m and 400m reps)

Warm-Up (10 minutes)

400m easy as: 100m freestyle, 50m backstroke, 100m freestyle, 50m kick, 100m choice. Focus on long strokes and relaxed breathing. Build pace slightly over the final 100m to prime the body for the main set.

Main Set

All intervals at CSS pace (your critical swim speed) or 5 seconds per 100m slower. Rest intervals are fixed — hold your target pace or back off; never shorten recovery to chase a number.

• 4 × 100m at CSS pace, 15 seconds rest between each
• 3 × 200m at CSS pace, 20 seconds rest between each
• 2 × 300m at CSS pace (or 5 sec/100m slower), 30 seconds rest between
• 1 × 400m at CSS pace — controlled, even effort throughout

Cool-Down (5 minutes)

200m very easy choice of stroke. Focus on breathing out fully underwater and letting the stroke recover naturally. No effort — this is purely parasympathetic recovery.

Coaching Notes

• The 400m closing rep is the key piece — if you’ve gone too hard on the 100s and 200s you’ll struggle here
• If you don’t know your CSS pace, use the 400m and 200m time trial formula to find it before this session
• To make it easier: add 5–10 seconds extra rest per rep; to make it harder: target CSS on all reps including the 400m with only 20 seconds rest before it
• Total main set distance: 2,900m; total session including warm-up and cool-down: approximately 3,500m