@mcb62 at 5.1 cm I would have expected closer follow up and more guidelines. Have you consulted with a thoracic surgeon yet? As a reference mine was repaired at 5.2cm as the surgeon considered it large for my body size. The size of the aneurysm is one variable but there are others a surgeon will consider when assessing timing for a repair (body size, family history, other illnesses, general physical health, geometry of the aneurysm, etc)

Exercise is important, you want your body at its best for when you need surgery but there are guidelines, no over exertion, no lifting heavy weights and exercises that lead you to hold your breath and/or grunt. BP spikes during those seconds and can lead to big issues with your aneurysm. Controlling your BP is paramount and kudos for quitting smoking and losing weight, that will go a long way.

Again I would consult with a very experienced thoracic surgeon in a major medical center ASAP to get you evaluated.

Take care