Also - Just because this keeps coming back to my age - I ran a 10k in February, I came in 274th (told you I'm slow) of the 273 people who finished before me roughly 70 of them were younger than me, that means 200 were older, including at least two individuals in their sixties and a dozen or more in their 50s. I really don't think physical fitness, particularly cardiovascular physical fitness, however you choose to pursue it, be it running, hiking, stairs, walking, etc, has to be about age!