In a 1993 film Dragon: The Bruce Lee Story there’s a scene where the main character sits at a typewriter wearing electrodes strapped across his chest and biceps.

The martial arts superstar is zapping his muscles so he bulks up without doing any exercise.

“Three minutes is like doing 200 push-ups,” he claims.

This technology, called electrical muscle stimulation or EMS, was explored by the Russians back in the 1960s to help athletes train, and it’s since been embraced by the likes of soccer star Cristiano Ronaldo and Olympic gold medallist Usain Bolt.

These days, EMS is promoted to people who want to get buff. You can even wear a whole-body EMS suit at the gym.

EMS proponents say that the technology, which sends electric impulses through skin and into muscle below to make them contract, “bypasses” the brain, triggering muscles to work and grow in a “smarter and more efficient way”.

Some ads say you can get your weekly whole-body workout in just 20 minutes — without lifting a single weight.

It sounds too good to be true, so what is the scientific evidence for these claims?

What’s the theory behind EMS?

Our muscles are made up of different “motor units”, each consisting of a nerve and the muscle fibres it activates.

One type of motor unit is smaller, contracts slowly and takes a while to get tired, while the other is larger, contracts rapidly and fatigues quickly.

The larger units use more energy but can generate more force. These are the ones that we use to build strength over time. 

When we voluntarily activate our muscles — by lifting weights, for example — our brain activates the smaller slower motor units first before activating the larger faster ones, says Swarup Mukherjee, a sports and exercise physiologist at Nanyang Technological University of Singapore.

“What EMS does is it reverses this natural recruitment order.”

And it is thought that by stimulating the larger motor units first, EMS can speed up the process of building muscle mass — and strength.

From medicine to elite sport

Manufacturers of some EMS gadgets have landed in trouble for overstating their claims on late night infomercials.

While some gadget claims might not stack up, there is a scientific basis for using electricity to stimulate muscles. In fact, the idea has been around for centuries, and has developed into an important way to exercise muscles when someone has an illness or injury.

“For patients that are unable to physically exercise for whatever reason, electrical stimulation can replace exercise,” says Gordon Lynch, who studies the use of EMS with the Centre for Muscle Research at the University of Melbourne.

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“The evidence is really strong that we can get adaptations in muscle and recruit muscles in a way that that can be beneficial.”

But, Professor Lynch says, it is less clear whether EMS works as a general fitness tool.

“There’s no real consensus about how to optimise this form of training for otherwise healthy people.”

Still, there are no shortage of online testimonials from people who swear EMS workouts are the way to go.

But what does the evidence say?

Some research, such as this small 2016 randomised controlled trial of middle-aged men, supports using EMS to build strength and lose fat.

And the technology’s “time-efficiency” and “joint-friendliness”  is seen by some researchers as attractive to those “unable or unmotivated” to do intense exercise.

A 2023 review by Dr Mukherjee of 10 other studies also found EMS increased the size of the muscles they stimulated in healthy adults.

And since muscle is one of the most energy-hungry tissues in the body, building them should also help burn fat, Dr Mukherjee says.

But, he cautions, building bigger muscles does not necessarily translate to the sort of strength that will make gym exercises or everyday activities easier.

In fact, none of the studies in his review found EMS improved such “functional” strength.

Other researchers who reviewed the evidence on whole-body EMS  concluded active people won’t get any advantage from the technology, although older sedentary populations may benefit.

One limitation of EMS is that it contracts static muscles, but to do specific activities our brain orchestrates a combination of muscles in a special way, Dr Mukherjee explains.

During bicep curls, for example, our biceps contract, while our triceps must lengthen and relax.

This is why there is a preference among proponents to combine EMS with traditional muscle exercises, Dr Mukherjee says.

Getting the right ‘dose’

Everyone’s muscles respond differently to EMS, Professor Lynch says, adding that this makes giving the right dose of stimulation a challenge.

“If it’s not enough, then you’re not going to get any benefit at all. And if you over stimulate, then you can cause muscle damage.”

Sport scientist Nicola Maffiuletti of the Schulthess Clinic, an orthopaedic hospital in Switzerland, agrees.

Traditional muscle building involves progressively — and carefully — adding heavier weights to a training regimen over time as your muscles adapt and get stronger.

But Dr Maffiuletti says it’s harder to know how much current to use to get the right stimulation with EMS.

“When you inject current you don’t know how to properly dose on an individual basis.”

Possible risks of EMS

Dr Maffiuletti is particularly concerned about the dose of current delivered by whole-body EMS suits.

These are a wetsuit-type outfit with electrodes that stimulate a number of muscles across the body at the same time.

He says it’s like “giving a pill” when we don’t know how much drug the pill contains, or what it’ll do to the person taking it.

“It’s not a cautious way to exercise.”

While painful muscles are to be expected after a muscle workout of any kind, Dr Mukherjee warns people should not experience pain at the time of receiving EMS — discomfort yes, but not pain.

In 2016 Dr Maffiuletti co-authored a piece in the British Medical Journal calling for better regulation of whole-body EMS suits after seeing people’s muscles break down in a condition called rhabdomyolysis, which can lead to kidney damage.

While there are fewer reports of rhabdomyolysis from EMS these days, he remains concerned about how well people are screened before using whole-body suits at the gym.

Even experts who support the use of whole-body EMS in general fitness warn of potential harms and the need for better oversight.

The US Food and Drug Administration has warned some consumer products have reportedly shocked, burned, bruised and irritated the skin of users, and interfered with critically important medical devices such as pacemakers.

If you are planning to fork out for EMS at the gym, Professor Lynch advises looking for a personalised approach with supervision by a professional like a physiotherapist who is trained in using the technology.

But he recommends making the most of more traditional forms of exercise and strength training first.

Finally, he adds, if weight loss is the goal you also really need to watch what you put in your mouth.

Delve into claims surrounding EMS in more detail on What’s that Rash? and subscribe to the podcast for more answers to more health questions.