For basic cardio fitness, I do stair climbing. It's as risk free as it gets and it raise your heart rate a good bit. I used to do it 20 minutes non-stop every o

For basic cardio fitness, I do stair climbing. It's as risk free as it gets and it raise your heart rate a good bit. I used to do it 20 minutes non-stop every other day and it kept me quite fit. Rock climbing when I can be bothered going to gym. Not lately.