Nobody ever asks me how to swim 375. It is always 400, and I understand why. Four hundred metres continuous is the distance where swimming stops being a set of lengths and starts being swimming. It is also the wall that most adults hit somewhere around 150, hanging off the end of the pool wondering what is wrong with their fitness.
Usually nothing is wrong with their fitness. The two things that stop people are almost never cardiovascular. You are spending too much energy per metre, and you are not getting rid of enough air. Fix those and the distance arrives on its own.
Why do I run out of breath before my legs get tired?
Because you are not breathing out enough, and the gas causing you trouble is carbon dioxide rather than oxygen. On land, exhaling is something you never think about. In water it becomes a job, because you must blow air out against the water with your face in it. Most beginners do the opposite. They hold the air in, turn to breathe, and then try to empty and refill their lungs in the same tiny window at the side of their mouth. There is not enough time, so each breath gets shallower than the last.
Researchers who studied people deliberately breathing less often during exercise describe the mechanism plainly: "The hypoventilation which occurs during RBF exercise is associated with a reduction in CO2 elimination," in a study published in the Journal of Sports Science & Medicine, where RBF stands for reduced breathing frequency. You are not so much starved of air as stuck with the air you failed to get rid of. That is the burning, panicky feeling at 150m, and no amount of fitness solves it while you are holding your breath.
The fix is unglamorous. From the instant your face goes back in, let air out in a steady stream, so your lungs are already empty when your mouth clears the water. Then all you have to do is inhale. I went through the whole progression in how to breathe in freestyle.
Is swimming 400m a fitness problem or a technique problem?
For most adults it is a technique problem wearing a fitness costume. The measurable difference between a beginner and an elite swimmer is not how hard they can work, it is how much speed they lose and regain inside every stroke cycle. Sport scientists call that intracyclic velocity variation. When one study compared the two groups, "IVV for elite swimmers was significantly lower (26%) than that for beginner swimmers at all swimming velocities," with elite swimmers varying by 7.28% against 9.80% for beginners, according to the comparison published in the Journal of Human Kinetics.
That matters because of what it costs. The same paper notes that "energy cost, as calculated by dividing total energy expenditure by velocity, was positively correlated with IVV, and suggested that higher IVV was related to low swimming economy." Every time you slow down inside a stroke, you have to accelerate your whole body through water again, and water punishes acceleration. Do that on every stroke of every length and you have burned through your 400 by the second hundred.
The other great energy leak is a low hip position, because a body angled downwards drags a much larger surface through the water. That one has its own article in why your legs sink when you swim.
How many lengths is 400m?
Sixteen lengths of a 25m pool, or eight lengths of a 50m pool. If your pool is 25 yards, 16 lengths gives you 400 yards, roughly 366m, which is a fair stepping stone rather than the real thing.
Do not count to sixteen. Count four hundreds, and let your brain tick over one block at a time. Sixteen feels endless at length three. Four blocks of four does not.
How slow should I actually be swimming?
Slower than feels right, at a pace you believe you could hold for 800. Almost every failed attempt I see is a 400 started at 100 pace. The first length feels wonderful, which is exactly the trap, because you have no feedback in the water telling you that you are overcooking it until the carbon dioxide catches up at 150.
If you want a target rather than a feeling, put a comfortable 100 time into the swim pace calculator and see what it implies over 400. Most people are surprised by how gentle the honest number looks. I went deeper into pacing in how to swim without getting tired.
Should I use breath holding or hypoxic sets to build up to this?
No, and the research is unusually blunt about it. The same reduced breathing frequency study found that "Training with reduced breathing frequency could not be realized at higher intensity of exercise due to the additional stress caused by such a breathing pattern. Therefore the improvement in aerobic endurance (considering peak oxygen uptake) could not be expected after this kind of training."
What it does produce is tolerance to a higher level of carbon dioxide, a real adaptation, but not the endurance you need here. Breathing less is not a shortcut to breathing better. Breathe every two or every three, whichever lets you finish a length without your stroke falling apart, and spend your effort on the exhale instead.
What is the fastest way to build up to 400m continuous?
Shrink the rest rather than stretching the distance. Your body already does 400m of work every time you swim 8 x 50. What it has not learned is to keep going through the moment where you would normally grab the wall.
So hold the volume steady and squeeze the gaps. Week one, 8 x 50 with twenty seconds rest. Week two, 4 x 100 with twenty seconds. Week three, 2 x 200 with thirty seconds. Week four, one 400. Measure rest in breaths rather than seconds if the clock makes you anxious: five slow breaths at the wall, then four, then three.
What do I do when I want to stop at 200?
Change something small instead of stopping, because the urge is almost always a signal you can answer rather than an order you must obey. Lengthen the next six strokes deliberately, unclench your hands, let your shoulders drop, and make the next three exhales longer than they need to be. In most cases the feeling passes inside a length, and you find out the ceiling was in your head.
The four week build, in one list:
- Week 1: 8 x 50 freestyle, 20 seconds rest, focused only on a continuous exhale
- Week 2: 4 x 100, 20 seconds rest, counting strokes per length and holding the number steady
- Week 3: 2 x 200, 30 seconds rest, deliberately easier than you want it to be
- Week 4: 1 x 400, broken mentally into four hundreds, not sixteen lengths
- Every session, start with 4 x 25 as slowly as you can swim without sinking
- Never start the 400 faster than your target pace, since there is no recovering that spend
- Add a length only when the previous step felt repeatable, not heroic
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