Lying on a bed of nails is literally a circus sideshow act meant to surprise and impress the audience into thinking that the person doing it has a superhuman ability to ignore pain.
But it's really not that big of a deal; lying on a bed of nails doesn't really hurt, and the reason why has to do with both physics and physiology.
First, the physics: As it's explained over at How Stuff Works, it's all about pressure, which equals force as divided over area. While one nail tip sticking out of the ground that meets your foot has a small enough surface so that the force of your foot coming down on it can pierce the skin, a bed of nails changes that equation. As Tracy V. Wilson writes: "But a bed of nails has lots of points that are close together — there's a lot of surface area for the body to cover. Hundreds of nails support the weight of your body instead of just one. Typically, your body doesn't exert enough pressure on any one nail for it to break the skin."
Now watch the "incredible feat" by Brad Byers in "America's Got Talent" video above (skip to the 2:49 mark.) Check out how many nails there are on his "bed." Now that you know about pressure and how it works, his trick doesn't seem all that impressive, right?
In fact, beds of nails were originally used by yogis in India to assist in meditation, and modern products that are like yoga mats with little spikes on them intend to do the same thing. My partner and I regularly use an acupressure mat called Halsa (a similar product is sold under the name Bed of Nails) that has brought us both real relief. He uses the pillow on his neck to help with neck pain, and I like the mat for helping with muscle pain after long runs. Some people have found it benefits back pain and studies (by the company itself) show that using the mats increases back temperature, indicating increased circulation to that part of the body, and also lowers the heart rate.
Acupressure mats and neck rolls may give some relief from back and neck pain. (Photo: Bed of Nails)
I'm not going to lie: When you first lie down on a mat like this, it's uncomfortable. They recommend that you start by wearing your clothes first, and work up to lying on it with a bare back. It's not as intense as a bite or a sting, but it's not exactly enjoyable.
For the first minute or two, you want to get off — but if you just breathe through it, your body's natural oxytocin (a pain blocker) will start flowing and then your endorphins kick in, leading to a real sense of relaxation and positive feelings. If you keep lying on the mat and breathing deeply, you will walk away after 10 minutes or so feeling lighter and happier — although you will have thousands of little non-permanent marks on your back from the spikes which definitely looks kind of crazy for a few minutes until they fade.
I've found that the day after long runs I often have sore muscles, and for me, lying on the acupressure mat alleviates my discomfort enough so I don't need to take an anti-inflammatory or pain medication for discomfort. My body is encouraged to produce enough pain blockers on its own, and my circulation increases on my back, butt and the back of my legs, which I believe leads stimulates the muscle enough to loosen up on their own.
If you're dealing with a chronic or occasional pain situation, the mats are an inexpensive fix that might work for you as well as they have for me.