Pain is a very interesting part of the human psyche. But it is not just limited to its psychological components, but also manifests itself in its physiological reactions and symptoms. These human, or rather animal behaviors are quite complex, and there is no easy way to put it. When it comes to devices that help reduce pain via various methods, the difficulty is quite similar. However, due to extensive research done and studies carried out, a lot of correlational factors have been found that can be controlled.
One theory behind the reduction of pain using TENS therapy is about endorphins. These are natural chemicals that are present inside our body and released to immediately relief pain. However, when the pain is extensive, the brain tackles it a little differently. The TENS devices help send signals as electrical impulses for the body to release more of these pain reducing chemicals, which helps in that relief when you operate the device on your body.
Another theory behind these electrical impulses sent to the brain is that it blocks the neural pathway. The way it successfully does it helps the natural nervous system to stop sending signals to the brain that indicate pain. This, in turn, helps stop the sensation of pain which gives you that immediate relief. The blockage of signals does not heal the wound but it simply hides the fact from your brain that the specified area in the body is still hurting. All of this is quite interesting, the neurobiology and the neuropsychology behind it. The concepts are very real, and if you want, you can try it out for yourself and see what happens. You can find such devices and its details on https://www.wellnessgeeky.com/icy-hot-smart-relief-review/.