Masters Descending Set: 400–300–200–100m Pool Session

Session Overview

The classic masters descending set — 400m down to 100m with reducing rest intervals — combines endurance loading at longer distances with genuine speed work at shorter efforts. It rewards pacing discipline and punishes early aggression, making it one of the most effective sessions for building triathlon-specific swimming economy across all event distances.

What You’ll Need

• Pool lane (25m or 50m)
• Swim goggles
• Pace clock or waterproof watch
• Pull buoy (optional, for warm-up)

Warm-Up (10 minutes)

Swim 300m easy freestyle with a pull buoy, focusing on a long body line and slow, deliberate stroke turnover. Follow with 4 × 25m at moderate pace (RPE 6) to get blood flowing to your shoulders and upper back. Rest 15 seconds between each 25m effort before beginning the main set.

Main Set

The descending set: each distance reduces, rest intervals reduce, and target pace increases progressively. Total main set distance: 1,000m.

• 400m at CSS minus 5 seconds per 100m (aerobic effort, RPE 6) — 60 seconds rest
• 300m at CSS pace (threshold effort, RPE 7) — 45 seconds rest
• 200m at CSS plus 3 seconds per 100m (slightly above threshold, RPE 7.5–8) — 30 seconds rest
• 100m all-out sprint (RPE 9) — full recovery before repeating if desired

Cool-Down (5 minutes)

Swim 200m very easy — any stroke you prefer. Use a pull buoy for the cool-down to completely off-load your legs after the sprint effort. Breathe deeply and let your heart rate settle well below 120bpm before exiting the pool.

Coaching Notes

• CSS (Critical Swim Speed) is calculated from your best 400m and 200m time trials — it represents your lactate threshold swim pace. If you do not know yours, estimate it as the pace you can sustain for a 1,500m all-out effort.
• Common mistake: the 400m feels easy, so you swim it faster than prescribed. This front-loads fatigue and costs you the 100m sprint. Discipline on the 400m makes the rest of the set work.
• Scale up: complete the full descending set twice through with 3 minutes of easy swimming between rounds. Total session distance becomes approximately 2,800m including warm-up and cool-down.
• This session fits well the day before a longer open water swim — it primes endurance and speed without the recovery cost of a harder interval set.