Is exercise-induced asthma strictly karmic in origin? What kinds of past trauma would cause it?

This is a good insight you have had, that exercise-induced asthma is appearing because of a karmic trigger that reawakens old business from the past in other lifetimes, and that can cause a revisiting of symptoms by cellular consciousness so that it will chime in whenever the trigger, of exercise in this case, provides a reminder of old trauma that impaired breathing. There were many times in past lives of almost everyone that required hard labor of one sort or another, many times on the part of children before they were truly old enough to carry their load or assume the level of responsibility expected of adults but were, indeed, pressed into duty anyway. There have been many situations involving imprisonment, often as a casualty of war, and many hard times requiring repeated and sustained brute force, to perhaps relocate via migration, while traveling tough terrain that was exhausting and sometimes fatal. So there are innumerable tragedies like drowning at sea, having an extreme effort during combat followed by a painful sudden death from a blow, spear, or sword, and so on, that can create an imprinting on the akashic records and the transfer subsequently into a new incarnation, energetically, by the Law of Karma to revisit the problem and seek a restitution through healing. That is what is on display with someone exhibiting exercise-induced asthma—having a physical strain causing increased respiration sets the scene and triggers past times when stress, similarly, resulted in tragedy.