The primary purpose of a TENS pen is to provide pain relief. The electrical impulses produced by the device can interfere with the transmission of pain signals to the brain, effectively reducing the perception of pain in the treated area. TENS pens are commonly used to alleviate various types of acute and chronic pain, including muscle soreness, arthritis pain, and neuropathic pain.

The use of the TENS pen,  typically applies the device directly to the skin over the painful area. The pen may have different settings for intensity and frequency of the electrical impulses, allowing the customization of the treatment to preferences and needs.  TENS pens also come with interchangeable massage heads or attachments to provide additional pain relief through massage therapy.

The TENS pen can also be used to stimulate muscle movement for exercise or testing nerve conduction of set muscles.  

It's important to note that while TENS pens can be effective and safe for many people, they may not be suitable for everyone, and it's always a good idea to consult with a healthcare professional before starting any new pain management regimen if you are not sure.