For cardio, the quickest and easiest things to do would be jumping jacks, jump rope, burpees, or jump squats. Sprints are good too except they take more time and are very hard on your body, so are only appropriate for advanced trainees. I’m not a huge fan of elliptical machines. Swimming is great, but I always found it a rather substantial investment of time as an exercise. Kind of like sprinting or, even worse, jogging, in the time commitment sense.
Generally, when comparing muscles and connective tissue, you’d be comparing those that are directly connected.