Electronic muscle stimulation (EMS) is used to aid rehabilitation following injury or surgery. It consists of electronic pulses delivered through a small device to your nerve fibres in order to create involuntary muscle contractions.
The electrical impulses activate muscles you might not normally engage, and when combined with deliberate muscle tension without bearing any weight, it works muscles hard and safely.
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 are awaiting recruitment when the contracting fibres fatigue. With EMS you can electrically stimulate these resting muscle fibres to improve their strength, thereby aiding rehabilitation or correcting muscle weakness.
Clinically, EMS appears to be more effective when the muscles are very weak and you have difficulty performing normal anti-gravity exercises.
EMS also works by providing an improvement in the recruitment of nerve conduction rates. Explained simply, it takes approximately 10000 repetitions for your brain to learn how to quickly send a message to your muscles via the quickest nerve pathways. This contraction pattern becomes your "memory engram". The more frequent your muscle is recruited the better your body becomes at finding the quickest way to recruit that muscle. EMS can potentially provide you with repeated contractions to accelerate this learning process.