I saw a pulmonologist over two years ago because my blood oxygen levels were too low (drops to 72%) after Covid. I was put on oxygen at home.

During my physical exam, the pulmonologist had me sit up straight in a chair and asked me to take a deep breath. My reaction was to hunch up my shoulders and try to suck in air through my nose. He said I was not using my diaphragm as my main muscle to breathe. I was doing opposite of what I should be doing - "chest breather". I was confused.

A fabulous physical therapist, who was a clinical instructor with her PhD at a large university hospital, worked with me to teach me diaphragmatic breathing, and also strength and balance training.

A practiced over and over, and slowly and I was able to train myself off of oxygen during the day during the day with light activity. Diaphragm breathing made all the difference! I am not a "chest breather" anymore.

There are YouTube videos on diaphragmatic breathing exercises.

Here's a simple article that helped me understand the physiology.