An increasingly popular fitness trend that involves stimulating muscles throughout the body using an electric current could cause damage and should be regulated, doctors have warned.
Whole body electrical stimulation (ES) involves the individual wearing a padded suit with electrodes that send impulses to the body to make muscles contract.
Gyms, which offer the service under the supervision of a trainer, claim benefits include fat loss, and increased fitness and muscle strength in about a third of the time as a conventional workout.
In a letter to the BMJ, published online on Wednesday, Dr Nicola Maffiuletti from the human performance lab at the Schulthess clinic in Zurich, Switzerland, and colleagues raised concern about the trend, which they said is based on “limited scientific evidence”.
The doctors said they have diagnosed three people directly who had ES and then suffered rhabdomyolysis – muscle breakdown – and heard about dozens more. Rhabdomyolysis leads to the release into the bloodstream of a protein called myoglobin, which can damage kidney cells.
The Israeli health ministry has decided to regulate such devices, warning that “uncontrolled, unregulated use may cause medical damage and endanger health”, and the letter’s authors want others to follow suit.
Maffiuletti said: “The danger is if you apply the current to the legs, the arms, the trunk, at the same time that is a lot of current. They are unable to quantify the dose, it’s not like when you lift three or five kilos [in the gym].
“If you applied it to me, then you, then my wife, then my child, the reaction of the skin and the tissue between the muscles is different so it’s a bad idea to think you can give standard dosage of currents to different people.
“It’s based on the perception of the person [receiving it] which is not reliable. It’s like taking a pill without knowing the dosage.”
The letter said “the true number of people injured by this form of exercise may be much higher but they are undiagnosed”.
Several gyms have begun offering ES in London and more are expected to follow across the country. But the UK is far behind the likes of Spain, where, according to Maffiuletti, 500 have begun providing the service in Madrid in the last five years.
Electric muscle stimulation, not for the whole body, was originally used by people who had received surgery, were immobilised or had been into space, said Maffiuletti.
Athletes said to have used it for training during rehabilitation include Usain Bolt, Rafael Nadal and Frank Lampard. But more recently, it has been adopted as an alternative form of exercise by healthy people.
Maffiuletti said that in low doses, and used for some muscles – but not the whole body – the treatment could be complementary to conventional exercise for people who train three or more times a week. He cautioned that at the clinic people are told to stay still during ES to avoid the risk of muscle damage, whereas many gyms recommend moving during the process.
The letter said: “Regulatory authorities, clinicians, and users need a greater understanding and awareness of the risk of ES-induced rhabdomyolysis, heightened ability to recognise this condition, and more diligent strategies to prevent this potentially harmful effect.”
None of the manufacturers or gyms the Guardian contacted responded to requests for comment.