An excellent cardiovascular exercise. Many people probably think that it's not so effective because it's not running and 'just walking', when really it can actually be just as good for weight loss as jogging.
Also, power walking is not simply walking at a faster pace. That's brisk walking. Power walking is walking at a fast pace (probably often even faster than brisk walking) with an arm swing.
Joe: Hey Alex, I'm going to be power walking a marathon tomorrow!
Alex: Ok, that's impressive, I guess.
Joe: Not just walking though. Power walking!
Alex: How hard can power walking a marathon be? You're just walking at a faster pace.
In a relationship, one's ability and willingness to leave the other, or "walk away" from it. The less clingy person can be said to have the walking power.
Roxanne is crazy about Todd, but Todd ca get another girl like her whenever he wants. You know he's got the walking power.