The polygraph is just an interrogation prop, like a cop holding a thick file of empty papers disputing your answers during interrogation "But we have a witness

The polygraph is just an interrogation prop, like a cop holding a thick file of empty papers disputing your answers during interrogation "But we have a witness statement that says you were in the building at the time". The random squiggles and wires attached to you are designed to stress you into screwing up your alibi/story and it's still effective enough they keep using it because people believe it actually works. If you try and defeat a fake prop by clenching muscles or some silly breathing techniques you've already lost because you believe it's real in the first place, much like how a voodoo curse works on those who actually believe and start to see the curse manifesting everywhere. It's job has been completed, to distract and stress you enough in hopes you begin to contradict your previous statements. The interrogators will always have props and fake analysis, like a "chair sensor" that can detect you trying to defeat the machine, or eye movement sensor, face reading 'expert', blood patterns they claim disputes your statements, a small wand with decorative LEDs and wires they claim can read chemical traces from your clothing as they wave it around and make a concerned face looking at a switched off laptop screen afterwards, or a fake phone on the desk "We've just learned your accomplice has been arrested and is in the next room making a deal, are you sure you don't want to change your story?". The Chicago Police are famous for arresting groups of people, and taking photos of one of them signing some kind of property release waiver, then presenting the photos to the other suspects claiming they have been snitched on. The most critical part of the interrogation with a polygraph is in the middle of the test where they switch off the machine and then continue to interrogate you "Let's just talk freely". Classic interrogation tricks (that still work), nothing more.