Any experiences with Frolov device and his theories on endogenous breathing?Konstantin Buteyko's work is a good place to begin from, as I don't think any single person has ever studied breathing as extensively as he did. Buteyko had a multimillion dollar laboratory built to him by the Soviet government during the space race, in which he connected people to machines that logged dozens of different parameters, it was from this data that his method was born. Modern Buteyko teachers have come up with all kinds of fancy exercises which unnecessarily complicate the process though. It's most convenient to just learn to breathe right and rack in an hour or two of light cardio every day. Then on top of that you can do a couple of >15 min sessions of designated relaxation in the way I instructed above. It typically takes about 15 mins of elevated co2 levels for the co2 setpoint to change, and about an hour of daily cardio/breathing exercise to make progress.
It's kind of a two-way street: poor posture leads to dysfunctional breathing and dysfunctional breathing to poor posture. Ideally your breathing musculature would give support to the whole upper body.