TENS and EMS machines are two different types of electrical stimulation devices that can be used for muscle relief and pain relief. TENS machines are typically used for short-term pain relief, while EMS machines are used for more long-term muscle rehabilitation. TENS machines work by sending low-voltage electrical impulses through the skin to the nervous system, which then interprets these impulses as a massaging sensation. EMS machine work by sending higher-voltage electrical impulses to the muscles, causing them to contract and relax. TENS and EMS machines are both effective forms of muscle relief and pain relief, but they should be used under the supervision of a doctor or physical therapist. TENS machines are available without a prescription, but EMS machines require a prescription from a doctor.