The title probably doesn't quite make sense right off the bat here, so let me explain. In high school track, we used to do some drills late in the season to both build power, focus on form, and increase our top end speed. For some of these drills, we'd use parachutes attached to a belt around the waist and run 100m sprints down the track, while the parachutes would create extra resistance and allow us to focus on technique. Obviously, these were the form and power component of the drills.
The other drill we'd do was one in which a bungee system was attached to one person at one end of the track and one person at the other end. By having the person pull the other, it would create the effect of forcing the person being pulled to run faster than their natural legs would have them go. The idea was to give the body a new stimulus of running faster than it is used to, stimulating your nervous system to adjust to the new speeds. These were short (maybe 50m), but pretty effective.
Anyways, the reason I am describing these drills is because I experienced something similar to that effect while running with Tucker yesterday. Most of the time, he generally runs within 1 ft of me, so there is minimal tension on his leash and we are both going about the same pace. But occasionally, this ratio gets flipped upside down. In some cases, he's like a rock I am dragging around (not that I am forcing him to do anything, its just that he needs a little encouragement to keep up!) and in others, he's like a bolt out in front of me and pulling me along.
So I've come to the conclusion that either of these scenarios isn't necessarily a bad thing for my running. If he is behind me, I am building strength by having a bit of extra force pulling me in the other direction, so I can focus on form and driving my legs (especially on hills). If he is out in front, he forces me to run a bit faster than normal, but with reduced effort since the force of him pulling me encourages faster running, which has a similar nervous system effect as the bungee drills.
Makes me wonder why I didn't have a dog to run with for all these years...man's best friend, right?