Thanks for the replies!
Gosh, a marathon sounds like misery! I wish I liked to run, it seems like a noble activity. I can bike at lowish speeds on the flat for 5 miles or so without feeling exhausted. A hill-climb will wind me briefly, but I recover quickly.
Equipment-assisted activities, like biking or inline skating, are much easier for me than running or jogging. Walking is easy and fun, but doesn't feel like it does anything for endurance.
I started primal for health and minor weight loss/shape change. Lost a clothing size since July & 12 lbs, basically just with dietary change.
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Primal since July 2011