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.
1 But I often like to add a few smashed cloves of garlic and some red pepper flakes, or a sprig of rosemary.  Cover with water: Cover the beans with water. There should be at least 1 inch of water above the beans. Bring the pot to a boil on the stove. (Note: If cooking red kidney beans or white cannellini beans, boil for a full 15 minutes.