EMS machine (or Electrical Muscle Stimulator) is essentially an electronic machine with the capacity to contract your muscles via an electrical current passed through your muscle. An EMS machine may be helpful in the initial phase of muscle strengthening. The electrical current may also assist pain relief, like a TENS machine, but pain relief is not it's main purpose.
How does EMS potentially help to Strengthen Your Muscles?
Electronic muscle stimulation (EMS) may help you to facilitate the strengthening of weak muscles. When you maximally contract a muscle, at best, only 30% of all your muscle fibres are in a state of contraction. The remaining 70% are dormant and awaiting recruitment when the contracting fibres fatigue. With EMS you can potentially electrically stimulate these resting muscle fibres to improve their strength. Clinically, EMS appears to be more effective when the muscles are very weak and you have difficulty performing normal anti-gravity exercises.