SORT of a pointless question.. but i had the thought run through my mind last night as i ran.. my newest neighborhood route takes me up and down some pretty good hills, and i definitely "run" up them, then slow down to almost a "jog" coming down- its been my experience that running down hill just stresses the tendons in the lower leg too much.. but so as to not enter the realm of "jog," as i define it, i make sure to keep my feet up and stay at a slow run. anyway... i've heard a number of definitions for both... speed, stride length, how much heal you land on, etc... personally, i define "jogging" as a fast walk with a hop- but you never leave the ground entirely, always with at least one foot continually touching the earth. "running" picks up both feet, so that you're in freefall for a fraction of a second every stride. speed has nothing to do with it- for i can easily accomplish a "run" thats significantly slower than probably most people's "jog," and likewise, i could probably accomplish a "jog" that's faster than a lot of people's slow "run." agree or disagree with my assessment? as to what difference it makes- i said "sort of pointless," above, however there is obviously a pretty significant difference between the two actions... i'd say a bonafide "run" burns a lot more cals than a fast jog, as you're pushing yourself up off the earth with every stride. likewise, the impact on joints must be significantly different- with a jog, as i define it, there's no crash back down onto a singular leg to absorb all that energy. as to which you should do- i make absolutely no guess. gonna be different for everyone... so this thread isn't really to debate the merits of either, just to differentiate and discuss.