Ha, yeah some eggheads speculating on a bunch of bullshit they'll never be able to prove. The only time I put on a dog collar, get down on all fours and bark is for my wife. But let's keep that between us and the internet.
But anyways, sweat glands, ok, all we got to do is keep the wind at our backs, no problemo.
Huck brings up an interesting point, before this degenerates into a firefight; there are good LBE solutions to carrying 35-50lbs, which may be of interest to civvy's doing whatever they're into. Then there are solutions for heavier loads, say in the 50-75 lb arena. Add into the mix are weather and terrain considerations.
So, in regards to military applications, where a squaddie may have to carry a bunch of shit, I think the external frame is king. Others may agree or disagree, but when it comes to really heavy-hauling, this is what I've seen, time and again. So this is why I like the short back, external ruck concept, in conjunction with a belt kit. I still believe this is the best all-around LBE solution, for military ops.
In regards to para-military activities, the insurgent still has to carry a bunch of shit, but in most cases, will not have the loads of a uniformed soldier. So this becomes a gray area, in that a short back external ruck and belt kit may still be worn, however, within this "weight class", so to speak, there may be viable alternatives, such as an A-PAK type design. I won't comment on competition or other activities, only to say if you are using that as a training tool, great; if not, well, wear whatever you want man.
However, when we get into hot/humid weather ops, another consideration is ventilation around back. Now I am not a scientist, but I can fucking-well tell you what an internal frame ruck on your back feels like on a hot summer day, humping up a mountain side. You are literally drenched. You are now wearing that 3L bladder. So, whether you are humping 35 or 75 lbs, if you are in hot temps, then an external frame ruck makes a lot of sense.
Then again, for cold weather ops, the internal frame may be a very good choice. If you don't have to worry about excessive sweating, then you might not need the stand-off of an external. You may even opt for chest-mounted LBE. And this opens up space for a long back ruck, with hipbelt. Which is beyond the scope of this thread, but here for illustrative purposes.
So yeah, again, tools in the tool box. In my personal opinion, the Crossfire DG-series, with external frame, and integrated bag and harness is the best solution for an armed citizen, doing longer range patrols, in extreme hot weather. If I was doing the same patrol in cold weather, I might use the same ruck, or go to an internal design. And to briefly touch on terrain. A road march on mostly smooth and level terrain is a far cry from a rocky trail up a mountain. Not to mention land nav in the woods. An internal might be a better choice for when balance becomes an issue. And good Lord, I don't even want to throw this one in, but, IF you have to wear BA, the external gives you room for that. Ideally I would want both. A design that converts back and forth would be nice. If not, then I'd pick an external.