I frequently read that dogs should only be attached to their running harness as we are about to start running and not before that or in any other occasion. They say that the dogs relate the harness to the fact that they may run and pull (which makes sense) and, therefore, that we should use another harness (or collar) for circumstances where we don't want them to pull (during walks and warming ups, for example).
In my humble opinion, however, this is just some kind of bullshit created by sellers or people willing to be seen as experts. My dogs wear a collar 100% of the time (even at home) because that's where they, for safety reasons, cary their ID and my phone number. Then, for walks, runs and competitions, we tend to use the (same) harness: just a comfortable and safe one.
But please don't get me wrong: I am not here to discuss which is the best running material, but the fact that people should be more critic to what they read. Of course relating the harness to the run might work and it is ONE way of learning the dog the differences - just like our dog knowing what we are going to do depending on the clothes or shoes we are wearing (work or walking/running shoes). But what these "experts" forget is that dogs are much more intelligent than that and they are also able to LISTEN to us.
If you go out for a training session with a (human) buddy, do you stop after warming up and ask him to change the shoes since you are about to start running? HELL NO!!! You just talk or through a gesture agree that you are ready to go, right?! So why does it have to be different with your dog?
My dogs doesn't rely on any equipment to know what they are supposed to do: they rely on me - on the informations I give them when we go out together. When we go out for a walk, they can SEE I am not running and understand that. If I start running, they do the same and once they are in front of me, they stay tuned on my voice commands - and we have lots of them, by the way: faster, slower, pull, keep going, good boy!, yes!, turn left, turn right, go ahead and stop are some (translated) examples.
Believe me: if you can teach your dog he is supposed to run hard only if he is wearing a certain harness, you might also be able to teach him a certain COMMAND for running (and another one for pulling hard, slowing down, making turns, stopping and etc).
...Unless you never thought him anything and just attach him on the collar because that's more convenient for you (since it's uncomfortable for him to pull from a collar)...