Most triathletes swim at one pace and wonder why they're not getting faster. This post breaks down the four intensity levels every swimmer needs to understand, and how to use each one to build endurance, speed, and race-day confidence.
If your swim sessions have started to feel like a chore; same pace, same distance, same result, there's a good chance you just not varying your intensity enough.
Most triathletes train at different intensities instinctively on the bike and in their run training. Intervals, tempo efforts, easy recovery sessions, the concept is familiar. But for some reason, it rarely carries over to the pool. You know the drill; you arrive at the pool, pick a pace somewhere in the middle, and swim laps until the time is up.
It's boring. And it stops working.
Here's how to fix it.
Why Intensity Variation Matters
Training creates adaptation by placing stress on the body. Different intensities create different types of stress, and different adaptations. Swimming at one pace, no matter how consistently, eventually stops producing meaningful change. Varying your intensity builds endurance, speed, and pace awareness simultaneously. When you get the balance right you'll be hitting T1 further up the pack and feeling significantly fresher.
There are four intensity levels worth understanding.
1. Recovery Pace — Zone 1, RPE 1–2
Easy, relaxed swimming. You should feel completely comfortable, breathing freely, with no effort to maintain the pace. Think of it as a slow walk on the beach, methodical and unhurried.
Recovery pace is used in warm-ups and cool-downs, and is particularly useful after a hard bike or run session. Even at this pace, focus on technique, there's minimal training stress here, so use the time well.
Pro tip: Turn your watch off or switch it to drill mode during recovery sets and put your fins on or grab your Pull Buoy.
2. Endurance Pace — Zone 2, RPE 3–4
A steady, comfortable pace you could sustain for a long time. Heart rate stays low, breathing is controlled, and it shouldn't feel particularly challenging. This is your base-building pace.
Pro tip: Most triathletes spend too much time here. If there's little difference between your sprint pace and your long-distance pace, or if you're swimming consistently but not getting faster despite decent technique, you're probably overdoing endurance pace and under-doing everything else.
3. Threshold Pace — Zone 3/Low 4, RPE 5–7
This is where the real swim fitness is built. Threshold pace; roughly your Critical Swim Speed (CSS) pace, is hard but sustainable. You'll be breathing heavily, and as the set progresses you'll feel increasingly uncomfortable. That discomfort is the point.
Threshold training builds muscular endurance, sustainable speed, and stamina. For most triathletes it offers the best return on time invested in the water.
Pro tip: Retest your threshold pace every 4–6 weeks. Your body adapts, and swimming off an outdated pace means you're no longer training at the right intensity, which is the most common reason athletes plateau.
4. Speed Pace — Zone 5, RPE 8–10
Fast, uncomfortable, and unsustainable without significant rest. Speed work develops top-end pace and mental toughness; both useful when you need to find space at the race start or respond to a gap.
Use it sparingly. A little sharpens you. Too much and you'll pay for it on race day.
Pro tip: If there's no meaningful difference between how fast you swim a 25 sprint and a 400 time trial, you need more speed work.
How to Use This
- Swimming miles at one pace but have no top-end speed? Add threshold and speed work.
- Strong in threshold sets but fading in the final 1000 of a long swim? Build your endurance base with more Zone 2 work and less rest.
- Exhausted after 50? Slow down. Build your endurance base before pushing intensity.
Varying your intensity won't just make your sessions more interesting; it will make them work. Get in the water and mix it up.