Years ago I bought one of the early Cotton Carrier bullet-proof vest-style camera support systems. I even used it a couple of times but overall found it too cumbersome and, I'm sorry to say, embarrassingly geeky - which isn't a Good Look in one's seventh decade. The problem of lugging around heavy camera gear is best addressed, I've since discovered, by carrying lighter equipment... In my case this amounts to M4/3 in the form of an OMD. For anyone who hikes using a regular strap the issue still arises of having the camera and lens bumping about against the body.
The Capture Clip system offers quite a simple solution in the form of an attachment which clamps onto a backpack shoulder strap or a belt. An Arca-Swiss compatible plate (it says here) mounts on the camera base and fits the clip with a locking button, plus an additional screw lock for those who feel that the latch isn't secure enough.http://peakdesignltd.com/capture/
Personally I still retain the Optech camera strap I've used for years - without any weight on it it's hardly noticeable and means you can sometimes allow the camera to hang from your neck rather than having to continually re-mount it on the clip. This is handy as although the clip isn't hard to use, if you're wearing a jacket or fleece the collar usually obscures the clip, which requires fairly precise alignment to mount the camera.
Anyway, for an OMD with the biggest lens I use (the Panasonic 100-300) fitted this system is by far the best and most comfortable way of wearing a camera whilst hiking that I've yet come across - you hardly notice it's there. It also makes changing lenses much easier, although this still seems to be something that is best undertaken whilst sitting down, and preferably by a person with three hands.
I usually use the Capture Clip on a Lowepro backpack that has both a sternum and waist strap. The camera's stability is aided by having the sternum strap done up although this is not critical. It might be if you had a full-size pro DSLR fitted. I've yet to try this with my D700 however I suspect that the additional weight, particularly with something like a 2.8 zoom on board, would twist the shoulder strap severely resulting in the camera bumping against the body to some extent.
I have encountered one problem with this product. The other day I was experiencing great difficulty mounting the camera on the clip although it looked to me as though the alignment was accurate enough. I had even greater difficulty getting it off again. What I later discovered was that it's possible to clamp the clip onto the shoulder strap in such a way that it tightens unevenly (shoulder straps vary in width, which is a contributing factor). In this case the knurled heads of the clamp bolts foul the base of the camera and cause jamming. This is really a design fault although once you are aware of the problem it's relatively easy to avoid a recurrence. I wrote an email to Peak Design who manufacture this device alerting them to the problem: as yet they have not replied, which scores no points.
That said, this device is practically indispensable for anyone who hikes with a backpack: I have yet to try it on a belt as I find belt-mounted gear a (literal) drag. I've run into a couple of other photographers whilst out recently who have immediately commented (positively) on the Capture Clip and enquired about it. A really useful accessory and not grotesquely over-priced - even in the UK...
To be fair to them I believe Cotton Carrier now have a similar product that has a broader backplate which may make it more suitable for bigger cameras. I have yet to see a user review.