I've never really thought about breathing patterns before, other than to try and keep my breathing as easy as possible at a given pace. What breathing patterns would a coach recommend for easy, tempo, threshold and all-out efforts?
The question about breathing rates is a great one, and it rarely gets asked.
When I was in my late 40s and beginning to train and race well (5Ks at 19:30-19:45, HM around 1:31), my max HR was 200 on the nose. 170 was my 85% HR, and corresponded to my marathon pace HR. That was the fastest HR where I could maintain a 3/3 rhythm without stress. Around 171-172, I'd switch to 3/2. Around 180, my 90% or threshold, I'd need to switch to 2/2.
2/2 thus became a defacto race-pace breathing rhythm for 5K through half marathons, although--crucially--I'd run the first three miles or so of a HM sub threshold, so I'd hold myself back by finding a pace where 3/2 would work and was comfortably sustainable.
As I've aged, those HRs have obviously declined. These days, at 62, my 85% HR is about 157-58. That's the highest HR I can comfortably maintain a 3/3 rhythm at. By 160, I'm 3/2. And by 168, I'm probably into 2/2.
I realize that this data dump seems kind of nerdy and OCD, but when you tune into such things, they're a huge help. Self awareness is good.