The thought process behind hiring Van Damme was that an agile martial artist would bring an extra layer of physicality to the movie monster. Van Damme recounted his audition process in an interview with Yahoo Entertainment, recalling that he jumped through the air and did the splits. A lot of Jean-Claude Van Damme stories are about doing the splits. There were a couple of problems, though. First off, the original Predator suit was a lot more cumbersome than the one in the final draft, looking less like a fleshy murder crab, and more like a cross between a nineties Power Rangers monster-of-the-week and a Skeksis from The Dark Crystal. Its backwards-jointed legs required that stilts be worn for long shots, so the fluid movements of a professional athlete got lost in the proverbial mix.
Also, and this is important, according to effects designer Steve Johnson, Van Damme wasn't aware that he'd signed on to wear a suit for the entire movie. He thought he was going to get a face-to-face rumble with Arnold in a Hollywood movie, then showed up, and instead was shoved inside a rubber monster costume.