Here's a couple of pictures that make the detached arm argument.
The first shows the two pieces of the musclesuit for my costume:
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The second shows the whole thing put together. The first time I test fit the whole costume I actually tore the armpit while checking mobility. I was able to patch it and reinforce it and make the patch seamless, but the continuing problem is if I raise my arms above shoulder height, I also run the risk of unsnapping the thong strap that holds the legs up and the upper body down. And even the Predator can't look cool trying to button his crotch back together.
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This is a picture of a buddy's predator. The finish work isn't quite as good, but the arms on this one are separate which allows for a greater range of motion.
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This is a shot of both of them. Notice how AVP inspired shoulder armor on his covers the seam between the arm and torso:
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Again, I hope you find this helpful.