It does not. I haven't given it much thought but I think it hangs on the shoulder straps so it doest not restrict the abdomen at all. I use the pack for other things like a map, power bars and stuff like that. On the other hand, I don't really do any high speed aerobic hiking
I have carried a daypack on my chest (while wearing a large pack on my back) on flat easy ground. I had no difficulty breathing and it did help my overall balance but I couldn't see my foot placements and would fear tripping and/or falling on the front pack (ie the camera).
While the balance might not be as good for a side-carry, I think it is overall more practical--I have carried an SLR on a bandoleer sling.
I have used the medium Clikelite DSLR chest pack for about 6 months and I love it, the harness keeps the pack secure to your chest so it doesn’t bounce around, but you can also loosen the bottom strap so it doesn’t restrict your breathing. Also having it’s own harness allows it to stay on while you remove your main pack, I used to use a standard DSLR pack attached to my sternum strap and had to remove it each time I remove my main pack, also being only attached to the sternum strap it bounced around and I was always worried about the sternum strap coming loose and my camera crashing to the ground. There is a slight issue with foot placement visibility but it’s something you get used to. The Clikelite packs are pricey but they are very well made and it has additional storage in the top to carry extra batteries and other small items.
I struggled with this for a bit. Now, I have a general idea what I will shoot before I arrive at the trailhead, so I bring what is needed for that. Usually, I shoot wide-angle landscapes, so I bring my 17-35mm. I then looked for the smallest bag that would hold my camera with that lens attached, and bought that. I removed the strap so that it doesn't take up space. It has compact pockets for holding a 2nd battery, my remote, extra memory cards, extra remote batteries, and even the allen wrench to take the ballhead clamp off. The whole thing is not too much bigger than a Nalgene. This goes right into the backpack, along with the ballhead in it's own pouch. The tripod goes on the outside of the backpack in different places depending on whether it's a day trip or an overnight. Shooting is coordinated with breaks, so it's not a big deal to pull it out of the pack each time. I usually only shoot at sunrise or sunset anyway.