As any of my swimmers will tell you, our pre-race strategy talk for IM always includes discussing their energy strategy (where to swim harder), and their breathing strategy. And of the two, I think the breathing strategy is more important.
The breathing strategy for single stroke events is pretty straightforward. Get into some kind of breathing pattern, and then make minor changes as the race progresses. As an example, we’ve spent a lot of time with our flyers reworking our technique so that breathing has minimal impact on the stroke. This means that we can start a 100 or 200 fly breathing every 2 or 3 strokes, but we don’t have to worry about the technique or rhythm falling apart if we have to go with breathing every stroke on the last length.
But for IMs, there’s a different breathing pattern for each stroke, and the pattern on one stroke can strongly affect the pattern on the next. Our prime consideration for a breathing strategy is to NOT be in any kind of breathing distress when changing strokes.
As an example, one of our biggest problems has always been that the fresh swimmer doesn’t breathe enough in the fly leg, and they’re start hurting for air when starting backstroke. At this point they either cut the underwater portion short (not ideal), or they push it and get further into breathing distress. And the strange thing about breathing in backstroke is that you can’t effectively breathe whenever you want. You breathe on the pattern that you train with, which tends to be every 2nd or 3rd arm stroke. Which means you can’t really catch up on your oxygen debt during backstroke.
And this brings us to the start of the breaststroke leg. In my opinion this is the most confusing and least understand transition of them all. Swimmers are trained to be tough, but not necessarily flexible in thought. So I often see fast IMers do a full breaststroke pullout when their lungs are clearly bursting. You can tell when this is happening when you see an incredibly rushed first stroke, or it takes them many strokes to get into their breaststroke rhythm.
To illustrate this point, I remember watching the heats of the women’s 400 IM at the 2015 PanAm Games in Toronto, and seeing quite a few only get to 6 or 7 metres with a full pullout. And then I saw two more women in the A/B finals also only get to 6-7 metres with a full pullout. That’s a lot of effort for such a short distance!
I started wondering about this years ago, and tested my (non-elite) IMers to see their time to 15 metres using a full underwater breaststroke pullout versus just a single dolphin kick, when both rested and tired. To my surprise, the dolphin-kick only underwater option for a single, rested 25 was only 0.1-0.2 seconds slower to 15 m than a full pullout, while they surfaced and got a breath up to 1 second earlier than the traditional pullout. But the BIG difference was when asking them to crank out hard 200 IMs and then watching their first length of breaststroke. In this case, doing just a single underwater dolphin kick was from 0.0 to 0.5 seconds faster to 15 m, while still surfacing for that breath roughly 1 second earlier.
Presumably, getting that breath one second earlier can also help the rest of the race as well. Especially as the freestyle leg is where we really see the impact of early breathing distress. This is when the stroke rate can drop, and the planned breathing pattern can break down.
So when my swimmers come back and can’t understand why their freestyle was so slow, I usually just point at their breathing pattern in the fly.
Summary
At least for my swimmers, an IM race includes an energy strategy, but our real emphasis is on smooth fast swimming while minimizing any early breathing distress. And being flexible enough to go to a single underwater dolphin kick for the breaststroke underwater if necessary.
Coach Rick - Mighty Tritons Swimming 
I’m only mildly embarrassed to admit that I really didn’t fully understand all the technical aspects of this discussion because I just don’t have any involvement with IMs and only minimal involvement with racing, so all the talk and terminology regarding pullouts and so forth is lost on me. But, your advice is totally consistent with my beliefs and what I tell all of my swimming students: if we didn’t have to breathe, swimming would be too easy. Breathing is key! And, of the two halves of the breathing process, exhaling is the one that deserves the most focus. You’ll inhale at some point whether you want to or not, but most of my students either refuse or forget to exhale. Which brings me to a question about something you said here. You mention an “oxygen debt.” This very well may be what is happening at your level of swimming. At mine, and more generally, the problem underlying the symptoms is not an oxygen debt but a CO2 surplus. Which is where the exhale becomes so important.
Hi Jerry
Sound like you understood enough to clearly see the issues. Yes, proper timing of exhaling is absolutely key to proper breathing. And if we can’t breathe properly, or at the right time, then the race is gone.
The technique for exhaling is honed in practice. Once we get to a competition, we assume that skill is in place, and then we can focus on breathing strategies to make sure we have enough oxygen in our system. Many swimmers have been trained to just tough it out – ignore the CO2 signals and keep going. But that’s not always the fastest way to race. This is why thought and preparation regarding breathing are key to a good IM