Walking for Weight Loss

Check out Linda LaRue's entry on Intent.com about Walking for Weight Loss. It's good. I myself have been walking a ton lately - walking the dogs, walking to work, walking for errands, etc. As summer creeps in, it's a nice way to feel the season. The Crunchless Abs guru talks about adding an incline to your route for help with the old butt. I hear that! Sometimes, though, I feel a distinct lack of internal energy on the walk - like it's an effort to put one foot in front of the other - I feel all out of whack, like my posture is off, my breathing is inadequate, etc. I wonder if it's related to diet, mostly, but could be low-lying asthma strain, I guess. Anyway, I wonder if other folks feel that, too, sometimes. Is that normal?