How many race-specific 400 sets can I do per week?

No more than 2 specific 400 sets per week. Combine them with aerobic base work and technique. The 400 freestyle demands heavy threshold loading and overdoing specific sets leads to accumulated fatigue without proper adaptation time.

How much rest between reps in a threshold set for the 400?

For long threshold sets (4×400m at CSS), 30 seconds rest is standard. For broken 400 (8×50m), 10 seconds. For pace 100s, 15 seconds. Short rest is key to simulating the cumulative fatigue of the actual race.

How do I know if my target pace for the 400 is realistic?

Use your CSS as a reference: your 400m target pace should be between 98-102% of your CSS. If you can't complete 4×400m at CSS pace with 30" rest, your CSS may be overestimated. Recalculate it with an updated 200m + 400m test.

WorkoutsPublished on February 23, 2026· Updated on April 12, 20262 min read

Best Swimming Sets to Improve Your 400 Freestyle

Swimer Team

International swimming coaches and high-performance technicians with 40+ years of combined experience.

Quick summary: The 400 freestyle improves with 5 types of sets: broken 400 (race pace), long threshold (4×400m at CSS), descending 200s, pace 100s (exact pace) and short VO₂. Do no more than 2 specific sets per week.

The 400 meter freestyle is one of the most demanding events in swimming: it requires aerobic endurance, threshold capacity and precise pace control. Improving your 400 time requires specific sets that train all these qualities progressively.

The 5 best sets for the 400 freestyle

Set	Quality	When to use	Block phase
Broken 400	Race pace	1×/week in specific phase	Weeks 5-7
Long threshold	Threshold capacity	1-2×/week	Weeks 3-7
Descending 200s	Effort management	1×/week	Weeks 4-6
Pace 100s	Pace memory	1×/week in specific phase	Weeks 5-8
Short VO₂	Aerobic power	1×/week	Weeks 4-7

Set 1: "Broken 400" (race pace)

8×50m at 400m target pace with 10" rest between each 50m. Add up your times and compare with your 400m PB. Goal: swim the broken in less than your PB + 1:20. This set teaches you exactly how your target pace feels and builds race confidence.

Set 2: "Long threshold" (TH zone)

4×400m at CSS pace (100% threshold) with 30" rest. The most direct set for improving your ability to hold pace over 400m. If you can't complete all 4×400m at CSS, your CSS may be overestimated — recalculate it.

Set 3: "Descending 200s"

4×200m descending (each 200 faster than the previous) with 30" rest. The last 200m should be at VO₂ pace. Trains negative-split effort management — the ability to finish stronger than you started.

Set 4: "Pace 100s"

8×100m at the exact per-100m pace of your 400m goal with 15" rest. If your goal is 5:20, swim each 100m in 1:20. Develops pace memory: your body learns to "feel" the correct speed without checking the clock.

Set 5: "Short VO₂"

12×75m at VO₂ pace (108% CSS) with 20" rest. Develops the aerobic power you need for the final 100m of the 400, where oxygen consumption capacity makes the difference between holding pace or "dying."

Key tip: The 400 freestyle is won or lost on splits. The best 400 swimmers do negative splits or very even splits. If your first 100m is 5+ seconds faster than your last 100m, you're going out too fast.

How to integrate these sets into your plan

Don't do more than 2 specific 400 sets per week. Combine them with aerobic endurance work and technique. In an 8-week block, race-specific sets intensify in weeks 5-7 and taper in week 8.

With Swimer, these sets are generated automatically with your exact paces based on your CSS. Calculate your CSS for free and get your personalized plan for the 400 freestyle.

Swimer unifies for the first time everything swimmers needed across five separate apps: AI adaptive training, official time import (RFEN, NCAA, European Aquatics), Strava, Live Pro Swimming (World Aquatics, European Aquatics, Aquatics GB, Swimming Australia, USA, NCAA), social network with 1v1 challenges and rankings, digital medal cabinet, 7D video analysis, Coach Portal and 24/7 human support — in one single app, in English and Spanish. Start free.

Step by step

1
Calculate your CSS and 400 target pace
Your 400m target pace should be between 98-102% of your CSS. Use the CSS calculator to get your exact training zones.
2
Start with broken 400s
Swim 8×50m at target pace with 10 seconds rest. Add up the times and compare with your PB to calibrate your pace.
3
Add long threshold sets
Do 4×400m at CSS pace with 30 seconds rest. This is the most direct set to improve your ability to hold pace.
4
Integrate pace 100s and short VO₂
Combine 8×100m at exact pace and 12×75m at VO₂ to develop pace memory and aerobic power for the final meters.