Hi
I'm considering a bent for comfort. My shoulders and hands are beginning to become more and more uncomfortable on my upright. My concern however is compromising my workout with a bent. Will I undo what I've accomplished as far as muscle etc? Sorry, I'm a novice.
Thanks, Susan

I wouldn't say compromise, but it is a different set of muscles. We call it "bent legs".

Most recumbents do not contribute much to upper body strength. However, that doesn't mean riding a recumbent isn't worthwhile toward maintaining fitness. It just means you will have to work on those muscles in some other manner. What recumbents can do is make the number of miles you ride increase a lot because it is so much more comfortable. You also will not find many "weight weenie" bikes and trikes in the recumbent category. I went from riding a few hundred miles a year on a high quality mountain bike to riding several thousands of miles a year. Sure I got tired, particularly at first, but no more numb hands and aching back.

WRT cardio benefit, how hard and for how long you go at it is more important than what you do. All activities that get you equally sweaty and winded for the same amount of time will have pretty much the same cardio benefit.
As for specific muscle groups, yeah, that will change a bit.

Recumbents are generally more aero than upright bikes - which means that at speeds of 15-20mph and faster, you can go faster with the same effort or the same speed with less effort. That's part of the 'bent vs upright training equation.
As with any cycling, it's all about heart, lungs and legs.

Even with an upright, upper body workouts should be done separately. (Uprights require upper body and core, but don't do much to build it.) As far as legs and cardio go, you get out what you're putting in. I found that bents encouraged me to work harder, because the harder I ride the more aero benefit I have over the uprights.