As you can see from the Summary, we start with a bed of nails. Only we turn the nails around, so that the pointy ends are down and the flat ends are what you lay on. And as you'll see in a moment, the nails aren't really nails....
Next, inside the frame where the nails are set, each nail is actually
free to move up and down a couple centimeters. Each nail is actually the core-piece of a solenoid. Since the operation of a solenoid generally pulls on its core, we also need a special spring (nonmagnetic steel) that can push the nail/core back out of the solenoid when the power is off.
Now we hook all the solenoids to a computer-control system. When you lay down on this bed and activate it, waves of gentle pummelings will impact your body, hopefully giving your muscle tension a "knock-out".