Thanks for your responses!
@jobo - Since you brought it up, I am dieting as well and have lost some weight, although not a significant amount yet. Because I'm so big, I think it will be a while before I lose enough weight to make my life easier.
Hmmm, I'm not sure short burst cardio is exactly my problem, although this probably depends on your definition of short. I don't have issues with doing a set of drills or doing sets of drills for 10 minutes. However, after 15 to 20 minutes of it without stopping for a break beyond turning around at at the wall, I get very worn down, particularly if there's lots of kicking involved. So if I could build up to doing intense (for me) cardio for 30 minutes straight, whether it be swimming, cycling, fast walking, whatever, I feel like that would help keep me going in class.
Squats sound like a good idea - my legs are weaker than I'd like and I'm not doing deep enough stances. However, holding deep stances while might be more beneficial.
Thanks for your input - I definitely want whatever I do extra to be low impact, which is why my mind immediately went to swimming laps. I'm already putting stress on my joints. I don't need more! However, low impact can still be intense cardio-wise, which I do think would be helpful. However, you do make a good point that I should be more patient with myself, especially since injury will hit the reset button! Perhaps I should limit anything extra to the days without training at the dojo. I'm also thinking there may be some value to doing this on the weekend - Saturdays and Sundays have been true off days, and Mondays have been a bit rougher than the rest of the week, which I assume is because I've been going into couch potato mode on the weekend. Sunday might be a good day for some swimming!
I actually do like this suggestion that you and
@Bruce7 made. One of my sensei also suggested walking more. However, I do have a finite amount of time that I can devote to exercise and I hate treadmills. Walking outside is an option, but it's winter here in western Oregon, which means rain, rain, and more rain. When the weather improves, weekend hiking will become an option, too.