[jome]

I've no idea what my residual volume is, but.

As trux points out, rv is a little bit different concept medically and in diving.

In medical sense, it means the volume left after you exhale fully.

In diving sense, you can go well below that by "cheating", ie using the external pressure or without the pressure change, using negative packing.

This latter definition is more interesting to us. It doesn't have that much to do with medical rv, but more with - as pointed out - flexibility of the diaphragm and other muscles and tissues around the chest. So a person who does a lot of negative stretching etc might get exactly the same result in an exhale test, but in diving, it makes a world of difference.

Would be nice to measure sometimes, this is a pure guess, but comparing to what I can pack in, I'd say when properly stretched etc I can remove 1.5-2 liters of air from my lungs with negative packing after reaching rv - comparing to the average rv that leaves "not a lot" in the lungs - and makes quite a difference in equalization.

How ever, off season I can hardly do 4-5 negative packs before I feel the squeeze.

Hmm, sorry I kind of didn't answer the question posted, but assuming you're interested in this from a diving point of view, I guess this makes some sense.