A few more exercise-related thoughts:
1. It is possible to do strength training at a speed and intensity that it counts as cardio, too.
2. This is MUCH more fun than doing normal cardio, which is boring.
3. It is also much more difficult and uncomfortable than regular cardio.
4. It's uncomfortable, but not painful, in the "oh, I'm getting healthier" way, not in the "oh, I'm breaking myself" way. That's how you know it's working.
5. It's NOT as much fun as just normal strength training, but still, all in all, the total fun is more. Also, since it's simultaneous strength and cardio, you save time. More difficult, more uncomfortable, faster, and more fun.
There is a fair bit of evidence out there that "high intensity interval training" -- HIIT -- is more effective at doing all the things you want cardio to do than lower-intensity ongoing cardio. Half an hour of intense strength training interspersed with brief breaks is better for you than an hour of running on a treadmill at a constant rate, unless, of course, you're actually TRAINING for distance running. Running for an extended period of time will absolutely make you better at running for an extended period of time, and will have lots of other benefits. And if you like running, it's a fine thing to do, especially if you're doing it in the real world where there are hills and things like that, rather than on a track or treadmill. Running is good -- unless you're as heavy as I am and running means "slamming piledrivers into your joints repeatedly", in which case biking and swimming are better choices...
But in terms of best results in least time, your best bet is mixing up a bunch of upper-body, lower-body, and core exercises, each at the highest intensity you can manage without actual PAIN, but WITH a lot of discomfort, with brief breaks in between.
Another thought: there is an xkcd comic which points out that exercise is a lot more rewarding if you think of it as grinding to level up stats.
I don't disagree, but I think that the "use it or lose it" skill degradation mechanic is among the dumber mechanics in the system. I mean, I get the advantage of it -- it forces different characters to actually create distinctions rather than all putting, like, one point into everything and all becoming the same -- but it just makes the whole thing less fun.