Perhaps you could elaborate which pieces you are thinking about, as the different parts have different solutions.
For example, it is most common for the Chest and Back to be separate pieces that attach at the shoulders and the side with parachute clips, magnets, Velcro, or snaps. The belt/Cod/Posterior section also is often split, with the connection hidden.
Most often, the biceps, forearms, thighs, and shins are all one piece. The forearms and the Shins are where some members encounter issues with them being one piece. The most common solution is for a member to simply scale them up just enough that their hand/foot can just fit through the opening but without the piece appearing over sized. The interior is then padded with a softer open cell foam to allow for the piece to remain in place.
Some members have developed some ingenious systems for the forearms and shins that allow for them to be split along seam lines and seal with magnets or Velcro, but, like I said, the most common method is to just make it big enough to fit through the smallest opening.
