I've long advocated the mental benefits of working out, and recently promised to offer some details about my own, somewhat peculiar regime. Here, I address the question: "How should I breath when I run?" My answer goes a long, long way beyond simply, "In-and-out."
Basically, I treat breathing as a mental exercise that accompanies and improves the brute physical aspects of running. By default, I run in a 3:4 pattern, inhaling for three steps and exhaling for four. On steep grades, in deep sand, or when sprinting, I might switch to a 2:3 or even 1:2 cadence. At other times, like yesterday, when I ran long miles on a flat dirt road, I might shift up to a 4:5 pattern, breathing in for four steps and breathing out for five. (I've also run in a 3:6 "gear," though it poses a problem for reasons I'll relate below.)
Most people who breath in step with their running unthinkingly fall into a 2:2 pattern, breathing in for two steps and breathing out for two. In contrast, I take care to combine a relatively short inhaling period with a slightly longer exhaling one. Why? Because we tend to generate more power when we exhale. Weight lifters, for instance, almost always breath out when working hardest. It thus makes sense, when running, to spend more time exhaling than inhaling.
I also choose breathing cadences that add up to odd numbers, a practice advocated by military trainers and others. Why? Because it helps to keep my stride symmetrical, ensuring that I start exhaling first on one foot and then, in the next cycle, on the other. A 2:2 pattern, in contrast, has you always pushing off the same foot at the most powerful part of your stride.
Those observations speak only to physiological issues, however. What about the mental side of the equation? Breathing in 2:3, 3:4, or 4:5 time has the salient benefit of not echoing any typical musical rhythm. Especially when I fall into a stretch of composing music, I tend to get tunes stuck in my head. Running in non-musical tempos gives me a reprieve from what would otherwise turn into an oppressively unremitting internal concert. (I take care to not mentally compose tunes in 5/4 or other exotic tempos while I run. Hence, too, the problem with a 3:6 cadence: It tends to stir up melodies written in waltz time.)
Lastly, and perhaps most importantly, breathing in time with my steps calms my restless mind. After years and years of practicing this sort of heart-racing meditation, I of course no longer need to count every breath. Rather, I simply choose a cadence and trust in habit to keep me on-track. Freed from the need to think about my breathing, and soothed by the now-familiar rhythms of lungs, legs, and heart working in concert, I enjoy miles and miles of peaceful reverie.