There is a difference between muscle inflammation and water retention/swelling. Inflammtion refers to injury/healing process and swelling is when the muscle absorbs more water. Two completely different things and two completely different reasons why it happens.
Long and short- you get water retention when you begin to weight train (new to it or coming back) because it's something "new". The muscle breaks down and during the repair process, water is absorbed into the muscles. I don't know the full process as I'm not an anatomy major, but most water retention from these activities is gone within 3 weeks; at about that time the body begins to adapt to these new stresses on the body. If you were doing power lifting constantly then you'd have chronic retention because you are constantly subjecting the body to more and more weight and powerful bursts. When you change up the routine you are asking the body to perform the exercises in a different sequence perhaps different reps and even switching out a couple of the exercises. You never stop training the body only train it differently. Bc the body isn't used to the "switch" it requires the muscles to adapt which is how you get DOMS. You can still get water retention but it isn't as great nor does it last as long again, because you never stopped training, only changed how you trained.
Inflammation is an injury- think arthritis, pulled muscle, twisted ankle, torn tendon, tenditits (anything ending in "itis" is referring to inflammation). This is due to an injury or even a build up of scar tissue that causes the soft tissues to swell from damage. Blood rushes to the injury, not water. This is to get oxygen to the damaged tissue to help in the healing process. This is the type of "swelling" that leads to medical issues and periods of time off and recovery- even surgery.
Things like RA and other auto-immune disorders are a chronic inflammation. I have FMS so it doesn't take anything these days to cause joint swelling and flu-like symptoms. I had to give up step workouts for that reason. In these cases it is important to listen to the body and not lift heavy weights. Heavy weights can aggrivate already inlfammation-prone joints and soft tissues. The chronic inflammation can lead to bone and joint breakdown like you stated and thus causing long-term consequences from anything to limited mobility to joint replacement and everything in between. You don't want to add fuel to the fire with auto-immune issues. This is why so many RA Doctors stress walking and swimming as your mainstays in exercise because they reduce the stress hormones which cause inflammation (moderate to vigerous exercise actually causes cortisol increases- a stress hormone). Strength training should be light to moderate with light to moderate weights or use bands/tubing and body weight. The idea is to stay functionally fit and strong, being able to work around the yard and house, play with the kids, lift your kids and boxes, and so forth- not to be a fitness competitor or body builder. Those activities will make your RA, FMS, and other conditions much worse and dibilitating.
This is a nut shell hopefully helps to answer some of your questions.
