For most triathletes, this is familiar.
You push off the wall feeling fine. The first 50 meters are manageable. Then your breathing picks up, your stroke starts to rush, and by 100 meters, you’re either stopping or hanging on.
The conclusion is almost always the same: I need to get fitter. But that doesn’t hold up.
You can ride for hours. You can run without that same level of fatigue. Your engine isn’t the problem. Yet in the water—the shortest part of the race—you’re exhausted in under two minutes.
So what’s actually going on?
Swimming doesn’t behave like cycling or running. In those sports, you can get away with inefficiency. In the water, you can’t. Every small mistake increases resistance and raises the energy cost of every stroke.
That’s why two triathletes can swim at the same pace, and one feels controlled while the other is completely gassed. The difference isn’t fitness. It’s efficiency.
The biggest issue is drag.
If your body position is even slightly off, your hips and legs drop. Now instead of moving cleanly through the water, you’re dragging your body forward. Every stroke costs more than it should.
Over 100 meters, that adds up fast. What should feel like a warm-up effort starts to feel like a sprint. Then your stroke begins to break down.
This is where most triathletes misread what’s happening. You don’t just feel tired—your technique is collapsing. Your catch slips, your stroke shortens, and your timing falls apart.
To compensate, you increase your stroke rate. It feels like effort, but it’s actually making things worse. Shorter, faster strokes cost more energy and accelerate fatigue. What feels like being out of breath is often just inefficient movement catching up with you.
Breathing makes this even worse.
In swimming, breathing isn’t just about oxygen—it directly affects your position. Many triathletes lift or over-rotate when they breathe, which drops the hips and breaks alignment. Now every breath is disrupting your stroke.
In open water, this compounds further. Anxiety, sighting, and race pressure exaggerate poor habits, making the swim feel even harder than it should.
Pacing is the final piece.
Most triathletes start slightly too hard without realising it. Because the stroke is inefficient, that small increase in effort pushes you into fatigue much faster than expected. By 100 meters, you’re already paying for it. It feels like poor fitness. It’s actually poor efficiency and poor control.
Here’s the shift most triathletes never make:
Swimming isn’t limited by fitness early on. It’s limited by cost.
Technique determines efficiency.
Efficiency determines energy cost.
Energy cost determines fatigue.
If you don’t reduce the cost of swimming, more fitness won’t solve the problem. This is why so many triathletes stay stuck. They swim more. They follow generic plans. They try to piece things together from videos. But none of that tells you what you are doing wrong. And without that, nothing really changes.
The athletes who improve fastest do one thing differently. They stop guessing.
They get clear feedback on their stroke, fix the specific inefficiencies, and follow structured progression that actually builds on those changes. Once that happens, everything shifts. The same effort produces more speed, and the swim stops feeling like survival.
This is exactly what we focus on inside BlackLine.
Instead of just giving you workouts, we show you what’s actually happening in your stroke. Through video analysis, we break down where you’re losing efficiency and what needs to change.
From there, you follow structured weekly programs and a full workout library designed to reinforce those fixes and finally swim with structure—not just add more volume.
It’s not about swimming more. It’s about swimming better, then building from there.
If you consistently feel exhausted after 100 meters, it’s worth questioning the assumption that fitness is the issue.
For most triathletes, it isn’t.
If you want to go deeper, you can join the BlackLine triathlete community here: BlackLine Athletes