Fitter or younger people than I am have far more ambitious programs, but we all do what we can.
Not including my two calisthenics days (which are, say 60% HIIT or regular cardio), I fit in two pure cardio days partly as recovery days from my weight-lifting days. Those two days are constructed (all workouts have to be planned) for heart strength and hill-hiking endurance and speed. Something like this:
- 10-min elliptical warm-up
- 5 mins misc jump rope drills. I'm working on one-footed, but it doesn't come easily to me
- 45 mins treadmill drill - A 5 min/1 min/30-second/1 min pattern, like this: 5 mins 3.2 mph walk at 8-10 incline; 1 min slow walk at 2 mph at 1.5 incline; 30-45 second sprint at 7-9 mph,;1 min slow walk; 5min jog at 4-5 mph with a 2 incline; 30-second "sprint" at 7-9 mph; then the 1 min slow walk. Rinse and repeat according to time availability. It's not boring because it is always changing.
- Finish up with 10 mins on the stairmaster, not too fast, to make sure I am a wobbly physical wreck by the time I am done.
I'm sure some readers can handle a more intense program, but I think mixing it up like this at whatever intensity one can handle is far more effective than monotonous trudging along for 60-70 minutes - that's a waste of time unless in cardiac rehab. Ya gotta push it to improve.