Sure feeling fat and out of shape is common with severe bloating. I have confirmed it is not just me that feels that even my butt and thighs swell when bloated. I don't know exactly about the weak muscles, other than that your body doesn't feel right and it can be ab spasms can cause a weak sensation all over -like after D. Today I was so bloated my rib cage hurt like heartburn but all over. Everyone experiences things differently and describes them differently. I have a lingo all my own with IBS that my husband understands, but when seeing a doctor terms like 'distension' 'spasms' etc work best.
The only things that work well for bloating are: staying stable/regular/taking acacia; drinking lots of fennel tea; eating often/slowly/standing while eating; exercising a lot or doing yoga and specific stretches; not wearing tight clothing/not napping/not holding in gas or stressing.
-------------------- IBS-A for 20 years with terrible bloating and gas. On the diet since April 2004. Remember this from Heather's information pages:
"You absolutely must eat insoluble fiber foods, and as much as safely possible, but within the IBS dietary guidelines. Treat insoluble fiber foods with suitable caution, and you'll be able to enjoy a wide variety of them, in very healthy quantities, without problem." Please eat IF foods!