How getting struck by a TASER affects the human body

TASERS, also called "electrical control devices," have been used by law enforcement since the mid-1970s, with the intention to help subdue resistant suspects without physical contact or the use of firearms.

The widespread use of ECDs, with more than a 1,070 estimated worldwide uses per day, as reported by TASER manufacturer Axon, has led many to wonder: What happens to the human body after being tased?

What is a TASER and how does it work?

A taser is a battery-powered, handheld device which delivers a short, low-energy electrical pulse. Two electrode wires are attached to the gun's electrical circuit. Pulling the trigger breaks open a compressed gas cartridge inside the gun and flings the electrodes into contact with a body and a charge flows into the muscles.

The taser delivers 19 short pulses per second over 5 seconds, with an average current of 2 milliamps, according to TASER manufacturer Axon. It creates an electric field, which stimulates nerve cells called alpha motor neurons to send an electrical impulse. The impulse travels to muscles and causes short, sustained muscle contractions.

The taser has two modes: the first, pulse mode, causes neuromuscular incapacitation as the neural signals that control muscles become uncoordinated, and muscles contract at random. The second mode, drive-stun, uses pain to get compliance.

The most commonly used device is the TASER X26, according to Axon.

The TASER's electric currents

The current -- either direct, DC, or alternating, AC -- is the rate at which electrons going down a wire travel per second. Alternating current is what is typically used in wall sockets and it's more dangerous, according to the Journal of the American Medical Association, causing more extreme muscle contraction.

An ampere, or amp, is the unit used to measure current. A small current -- 200 microamps –- applied directly to the heart can cause a fatal rhythm called ventricular fibrillation.

However, TASER currents don’t reach the heart. Humans have protective mechanisms: The skin, which provides high resistance to electricity, and soft tissue, which surrounds muscles and organs like the heart, also reduce the current.

For example, a current applied to the arm will be reduced to .001 percent of the original signal by the time it reaches the heart. TASERs have a 2 milliamp current and it takes at least 1,000 milliamps -- 1 amp -- to injure muscles, nerves and the heart. Higher amps, starting at 10,000 milliamps or 10 amps, cause the heart to stop and produce severe burns, according to the U.S. Centers for Disease Control and Prevention.

The TASER's effect on the human body

On skin, the most common affects are superficial burns or small puncture wounds, caused by the metal probes that deliver the current not being immediately pulled off after a person has been tased. Scrapes are often seen across the skin surface because the person shocked by the TASER my convulse uncontrollably.

TASERs cause muscle contractions, but do not appear to trigger the release of the muscle enzyme associated with muscle cell damage -- creatine kinase. If levels of that enzyme are high, it causes a condition called rhabdomyolysis, which can lead to kidney failure. Current research has shown that the muscle contractions induced by the TASER cause a small increase in CK, but do not appear to pose a direct risk for rhabdomylosis, according to a review of research by Forensic Science International.

For people without heart isssue, the electrical discharges of the TASER device are too short to affect the heart muscle or cause abnormal heart rhythms. Even for those with heart conditions, the proper use of the device does not appear to cause issues. One of the first study of TASERs on humans, published by the Academy of Emergency Medicine in 2006, looked at their effect on individuals with a known heart disease or diabetes. The study participants were shot in the back with a TASER and researchers measured blood markers of heart damage and did a test called an EKG, or electrocardiogram. They did not find any negative effects.

Complications related to the brain or nervous system are rare, but do occur, including loss of consciousness, seizures, abnormal brain activity and confusion. This is more likely to occur if a subject is shot at a close distance or directly to the head, which is not usually the case since those are not the recommended targets. The probability of causing a seizure is very low.

TASER strikes have contributed to a few cases of falling, which can cause brain injury.

Serious injuries represent less than one percent of injuries from TASERs, as noted in a 2009 study published in the Annals of Emergency Medicine that looked at more than 1,200 uses of conducted electrical weapons by law enforcement officers against criminal suspects.

Of course, police officers and medical personal should assess subjects subdued by a TASER for injuries. Existing medical or psychiatric conditions and the use of alcohol or drugs in the suspect may lead to behavior or reactions after the use of the TASER that need medical evaluation.