Read this if you are new to swimming
A swim set looks like code the first time you see one. It is not. Three numbers, one word and a rest time — that is the whole language. Here is how to read it, and why you should stop just swimming lengths until you are bored.
One line, decoded
8 × 50 m free · zone 4/8 · rest 20 sec
- 8 × — do it eight times.
- 50 m — each one is 50 m. In a 25 m pool that is two lengths, there and back.
- free — front crawl. Other strokes are written out: back, breast, fly.
- zone 4/8 — how hard, on a scale of 1 to 8. Four is “hard but controlled”.
- rest 20 sec — after each 50, stand at the wall for 20 seconds. Then push off again.
That line is 400 m of swimming and roughly 8–9 minutes of pool time. Nothing else is hidden in it.
The intensity scale, in plain words
| Scale | What it feels like | Can you talk? |
|---|---|---|
| 1/8 | Very easy, recovery | Full sentences |
| 2/8 | Easy, all-day pace | Yes, comfortably |
| 3/8 | Steady, working but calm | Short sentences |
| 4/8 | Hard but controlled — threshold | A few words |
| 5/8 | Very hard, breathing heavy | No |
| 6/8 | Race pace | No |
| 7/8 | Near-sprint, hurts, still controlled | No |
| 8/8 | All-out sprint, 15–25 m | No |
Most of a good week sits at 2–4. Five and above is the seasoning, not the meal. The full table with heart rates and lactate values lives in the glossary.
What “rest” actually means
Rest is time standing at the wall. Look at the pool clock when you touch, add the seconds, push off. That is it. Rest is not a break from training — it is what keeps the swimming fast enough to be worth doing. Twenty seconds is short; it should feel like you only just recovered.
Squads sometimes use a send-off instead (“leave every 1:40”), which needs a big clock and a lane that agrees. Every session here uses rest, because it works alone in a busy public lane. More on that in rest times vs. send-offs.
Why not just swim non-stop for 45 minutes?
You can, and on some days you should — long continuous swimming is real training. But if it is the only thing you ever do, three things happen.
1. You only ever practise one speed
Swimming straight through settles into the pace you can hold while thinking about something else. Your body gets very good at exactly that pace and nothing either side of it. Sets force you to visit other speeds — that is where new fitness comes from.
2. Technique quietly falls apart
Front crawl is a technique sport before it is a fitness sport. After twenty unbroken minutes your stroke shortens, your legs drop and you spend the rest of the swim rehearsing a worse stroke. Short repeats with rest let you swim each one properly — and drills only work at all when you are not exhausted.
3. Nothing is measurable
“I swam for 45 minutes” tells you nothing about whether you are improving. “8 × 100 m holding 1:45” tells you everything, and next month you either hold 1:42 or you do not.
Rest also lets you swim more total fast metres in the same hour. Eight 100s at threshold with 20 seconds rest is a harder, better stimulus than 800 m straight — for the same distance and barely more pool time.
Your first three sessions
- Get comfortable: 400 m easy warm-up, then 8 × 50 m at zone 2–3 with 20 seconds rest, 200 m easy to finish. About 1,000 m.
- Add technique: same shape, but make four of the 50s a drill — one arm, catch-up, or distance-per-stroke counting.
- Find your pace: swim the CSS test (400 m and 200 m, both hard). Save the result and every set you generate here prints the time you should be hitting per repeat.
Pool etiquette, briefly
- Slower swimmers to the slow lane; overtake at the wall, not mid-length.
- In a circulating lane, swim on the right and turn on the corner of the wall.
- Stand in the corner of the lane during rest so people can turn.
- If you need to stop mid-set, do it at the wall, not in the middle.