Most improvement in swimming comes from interval training. Continuous easy swimming builds a base but won’t make you significantly faster. Intervals push your pace, build lactic tolerance, and improve your cardiovascular ceiling. Here’s how to structure them.
The Anatomy of an Interval Set
Every interval set has four variables:
- Reps: How many repetitions (e.g., 10)
- Distance: How far each rep is (e.g., 100m)
- Interval: Total time from start to start (e.g., 2:00 — meaning you start each rep on the 2-minute clock)
- Target pace: How fast to swim each rep (e.g., 1:45)
Written out: 10×100m on 2:00, target 1:45 means you swim 10 reps of 100m, starting each one when the clock hits 2:00, aiming to finish each one in 1:45. That leaves you 15 seconds of rest.
Three Types of Intervals
1. Threshold Intervals
What: Sustained effort at your lactate threshold — the fastest pace you can hold for 20–30 minutes.
Format: 6–12 reps × 100–200m, short rest (:10–:20), consistent pace.
Purpose: Builds your aerobic engine and raises your sustainable race pace.
Example: 10×100m on 1:50, hold 1:38–1:42 each rep.
2. VO2 Max Intervals
What: Hard effort that pushes your cardiovascular ceiling — 90–95% max effort.
Format: 4–8 reps × 100–200m, longer rest (:30–1:00), fast pace.
Purpose: Improves your top-end speed and cardiovascular capacity.
Example: 6×100m on 2:30, hold 1:25–1:30 each rep.
3. Sprint Intervals
What: Maximum effort for very short distances.
Format: 10–20 reps × 25–50m, full recovery rest (:60–:90), all-out pace.
Purpose: Develops neuromuscular speed and fast-twitch fiber recruitment.
Example: 12×25m on 1:00, sprint each one.
How to Build an Interval Session
A simple weekly structure for a swimmer training 3×/week:
| Session | Type | Example |
|---|---|---|
| Session 1 | Threshold | 10×100m on 2:00 |
| Session 2 | Technique / easy | Drills + easy 2km |
| Session 3 | VO2 or Sprint | 6×100m hard, or 12×25m sprint |
Don’t do two hard interval sessions back to back. Your nervous system needs recovery between high-intensity sessions.
Pacing Discipline
The most common mistake in interval training: going too fast too early.
If your 10×100m main set shows 1:30, 1:33, 1:38, 1:44, 1:52, 2:00… you’ve blown up. Rep 1 was way too fast and you degraded significantly.
The goal is consistent splits. Rep 1 should be close to rep 10. If you can’t hold even splits, either the target pace is too aggressive or your interval rest is too short.
Progressive Overload
Every 2–3 weeks, do one of the following to keep improving:
- Reduce rest by :05
- Add 1–2 reps to the set
- Drop target pace by 2–3 seconds per 100m
Small, consistent increases over months produce big results.