HIEMS: how high-intensity muscle stimulation works

What is HIEMS?

HIEMS is a commercial term associated with high-intensity electromagnetic muscle stimulation. In scientific research, the acronym HIFEM is often found. Designations, parameters and energy combinations may vary between devices, so results from one device should not be automatically attributed to another.

The technology is non-invasive: the applicators are placed on the area, without needles or incisions. The objective is to stimulate specific muscle groups through a pulsed magnetic field.

How does a magnetic field contract muscle?

The magnetic field induces a small electrical current in the motor neurons, causing the muscle to contract without voluntary command. Throughout the session there are cycles of contraction and rest, the intensity of which is progressively increased.

These contractions are not the same as a complete workout. Exercise involves coordination, progressive load, cardiovascular system, mobility and multiple muscle groups. Technology concentrates the stimulus in one area and should be seen as a complement, not as a shortcut to the global benefits of movement.

For what purposes might it make sense?

The demand is mainly associated with toning and defining the abdomen and glutes, although some equipment includes arms, thighs or calves. The best candidate is not just defined by the zone: the starting point, body composition, muscle function and expectations count.

The FDA emphasises that non-invasive body contouring does not treat obesity or provide the health benefits of weight loss. If the main priority is to lose weight, correct pain, recover from injury or treat diastasis, the assessment must guide the appropriate approach.

• Stimulate and tone selected muscle groups.
• Support an aesthetic goal of greater localised definition.
• Complement an already structured routine of movement and self-care.

What do you feel during and after the session?

The applicators are positioned on the clothing or directly on the area, depending on the equipment. The intensity starts low and increases to the tolerated level. You can feel the muscle contracting strongly and rhythmically; the experience can be intense, but it should not be painful.

Afterwards, there may be muscle fatigue, sensitivity or a sensation similar to that of a demanding workout. The FDA identifies muscle pain and cramps as possible complications of magnetic field devices. Persistent or unexpected symptoms should be reported.

What does the evidence say — and what do we still not know?

A systematic review published in 2024 brought together 15 clinical studies of HIFEM, alone or combined with radiofrequency. Favourable changes in muscle thickness and abdominal fat have been described in several studies, but the protocols, equipment, samples and measurement methods were different.

Much of the research involves small samples, short follow-up periods and links to industry. This does not invalidate the findings, but limits certainty about how long effects last and whether they apply beyond the populations studied. The appropriate wording is “may support”, not “guarantees”.

Studies combining HIFEM with radiofrequency do not assess magnetic stimulation alone. If the device used does not include radiofrequency, those figures cannot be promised for HIEMS on its own.

Who needs a specific assessment before treatment?

Strong magnetic fields can interfere with implanted electronic devices and interact with metal in the area. Pacemaker, defibrillator, neurostimulator, metal implants, recent surgery or other devices must be communicated before any session.

Pregnancy, relevant disease, undiagnosed pain, hernia, changes in sensitivity or injury to the area require screening. The exact list of contraindications depends on the equipment, so the team should consult the manufacturer's instructions and not just a generic protocol.

How to assess whether it is working?

Before starting, choose an indicator consistent with the objective: feeling of firmness, standardised photograph, perimeter or other agreed criterion. The weight on the scale, alone, does not measure localised toning.

Agree on a reassessment date and ask what will happen if progress falls short of expectations. Consistent physical activity, eating and sleep habits continue to influence body composition and the maintenance of results.