Wow! Heart rates in the 40s and 50s! That is a true sign of your fitness!
Since my knees are bad, I don't run. (Doc would kill me if I did!) I do walk, and have gotten up to 2.25 miles in 35-40 minutes, which isn't too bad of a walking speed... not to mention, it's all that my knees can handle.
Swimming.... look out! I could swim forever, and ever, and ever and keep a decent pace. LOL I may not have good form, but, by golly, the endurance/stamina is there!

As far as treading water... could do that forever too.
I would love to be able to bike, but I don't even own one. I kinda figure, why put the money into it when I have no place to "safely" bike around here. I'm surrounded by busy roads and interstates. The ONE place that I have considered riding, I decided not to, cause I just don't trust the traffic. I'm also a Paramedic (obviously... the screen-name

) and visions of previous bicyclist patients run thru my head... and I think... "Oh, no! They weren't supposed to bend/twist right there!" Or, "Oh, is that their shoes laying 100 feet away?" Or, worst case... "I really hope they didn't feel that!" Or, "They didn't feel a thing." I just can't bring myself to ride a bike around here. That said.... I truly respect those that do ride, and give them ample room when I drive up on one.
