Position will dictate breathing ability. The most optimal position for breathing is with the spine straight, to provide access to the diaphragm and minimal compression on the lungs. If you hunch over or get into another sub-optimal position, you’re going to limit your maximum ventilation efficiency by restricting the airway and changing the demands on the respiratory muscles.
Obviously, not all exercises can be performed in a neutral spine position, so understanding how position effects breathing patterns is another crucial teaching step in the early stages of a training program.
One strategy for assessing breathing abilities is to use subjective measures of breathing volume in various positions. To do this, first start lying supine (flat on your back) in an optimal breathing position. Take a slow, full nasal inhale, focusing on filling the lungs and expanding the entire ribcage 360 degrees as much as possible. That full inhale is your current breathing capacity. Now move into different positions, starting with less stressful ones like quadruped, half kneeling, and standing. Then move into more demanding positions like a high plank, squat hold, or hanging from a bar. Hold these positions and perform the same breathing task, noticing the differences in tension, your ability to access the diaphragm and breathe deep into the belly, and whether you’re able to expand the ribcage 360 degrees.
Isometric holds — such as planks and side planks — are great ways to assess and train these breathing abilities, due to the ease of increasing or decreasing the intensity, and ability to create focused practice on the breath itself, since there is no distraction from movement. Yoga is a good example of using static positions to focus on the breath, and you can do the same during mobility work.