The science behind HIEMS

Lie down, have paddles strapped over your abdomen, and for the next half hour your muscles contract harder than you could make them contract yourself. You are not doing anything. You cannot stop it either.

That is the part people find strange about it. The muscle work is happening to you rather than being performed by you, and the soreness the next day is identical to the soreness after a hard gym session, because functionally it was one.

Worth clearing up, because the terms get used interchangeably and they describe different technologies.

Electrical muscle stimulation, the older and more familiar of the two, sends a current through pads placed on the skin. It has been used in physiotherapy for decades, it makes muscles contract, and it works mainly at the surface. The current has to travel through your skin to reach the muscle, which limits how hard it can push before it becomes uncomfortable.

HIEMS, high-intensity electromagnetic muscle stimulation, is what LMC uses. It generates a focused magnetic field rather than passing current through the skin. The field passes through skin and fat without stimulating them and induces electrical currents in the motor neurons of the muscle itself, reaching as deep as around eight centimetres. Because the skin is not the delivery route, the intensity can go far higher without discomfort at the surface.

When you contract a muscle voluntarily, you never recruit all of it. Your nervous system holds fibres in reserve and cycles through them, which is a sensible protective arrangement and also the reason a single set never fully exhausts a muscle.

HIEMS bypasses that. The field is delivered at a frequency high enough that the muscle cannot relax between pulses, so it holds a sustained contraction recruiting close to every available fibre. This is called a supramaximal or tetanic contraction and it is not something you can produce on purpose. A thirty minute session delivers in the region of twenty thousand of them.

The numbers behind that are worth seeing. The equipment generates a magnetic field of up to seven Tesla, delivered in pulses lasting three hundred millionths of a second. Two applicators run at a time, and the areas typically treated are the abdomen, buttocks, arms and thighs.

That is the whole proposition. Not a substitute for training, but a level of muscle recruitment that voluntary effort cannot reach.

Muscle grows partly through satellite cells, which sit alongside muscle fibres and are activated by demanding work, then fuse with the fibres to help repair and thicken them.

Studies examining tissue after HIEMS have found satellite cell content increasing by around 30 percent, which sits close to the 36 percent increase measured after twelve weeks of conventional exercise training. The mechanism is the same one training uses. The stimulus is delivered differently.

There is a secondary effect on the fat sitting over the treated muscle. The intensity of the contractions raises local metabolic demand sharply, and research has recorded reductions in the fat layer above treated muscle alongside the increase in muscle volume.

MRI studies measuring the rectus abdominis before and after a course have recorded increases in muscle volume ranging from about 4 to 21 percent across participants over three months. Pooled clinical data covering more than 500 patients reports averages in the region of 25 percent more muscle and 30 percent less fat in the treated area, with abdominal circumference reductions averaging around 4 centimetres.

One finding is worth separating out. Studies have recorded reductions of roughly 19 percent in the width of abdominal separation, the gap between the abdominal muscles that commonly persists after pregnancy and does not always close with ordinary core exercise. If that is your reason for looking at this, raise it specifically at your consultation.

Reported side effects across the literature are minimal. Muscle soreness in the day or two afterwards is the usual one.

The research on HIEMS is younger and thinner than the research on cryolipolysis, and a good deal of it has been funded by the companies who make the devices. Some independent researchers have argued that the measurement methods used in these studies do not reliably demonstrate change that is meaningful in practice.

That criticism is worth knowing. It does not mean the technology does nothing, and the MRI evidence for muscle volume increase is reasonably solid. It does mean the more expansive claims made about it in the industry are ahead of what has been properly established.

HIEMS builds and defines the muscle it is applied to. It does not make you fitter, it does nothing for your cardiovascular health, and it will not counteract an eating pattern working against you.

It also treats one area at a time. Strength built in your abdomen through a course of treatment is exactly that, and it does not transfer to the rest of your body the way progressive training does.

Used as part of a contouring programme it does a specific job well: adding density and shape underneath skin that has been firmed and fat that has been reduced. Used as a replacement for exercise it will disappoint you.

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