It could be many things. It could be from slouching or sitting in a way that is causing the diaphragm to be compressed. Do not try to over straighten, just think of relaxing the muscles and allowing yourself to fall into a natural position. It could be injury from working out and doing crunches or other movements. It could be a stomach ulcer.
Another option is to blanch green beans quickly. Blanch your green beans by boiling them for 3 or 4 minutes. This removes the skin of your green beans. You want your beans to be somewhat tender, yet have a little bit of crispness to them. Determine the crispness, by how long you boil them.
The recipe. Processing time: Half-litres (pints) 20 minutes; litres (quarts) 25 minutes. Green beans are very easy to can; most of the work is in the prep. Wash the green beans, change water, then re-wash the green beans, and give them a final rinse under running water from the tap as you lift them out of sink.