I maybe understand your question - when I lose fitness, I am not aware of lost fitness unless I try to lift a heavy thing again or run distance, at which point it becomes clear. In that vein, I had decent cardio at some point, so that might be part of why the breathing techniques don't really add much to it.

As far as meditation - it's very hard to draw a mental baseline. The only sort-of scientific, sort-of reliable way I know is measuring your working memory.