Both devices work the same way. A coil in the applicator produces a rapidly changing magnetic field. That field sets up a current in the tissue underneath. The current then acts on motor nerves directly. The muscle contracts whether you want it to or not, and harder than you can contract it yourself. The published term for this is supramaximal contraction.
What the NEO adds is radiofrequency energy delivered from the same applicator at the same time: That is the whole difference in hardware.
The interesting part is what the radiofrequency is claimed to do. It is claimed to do two different things, on two different filings. On the filing that carries the fat and circumference wording, performance testing shows a therapy temperature of 40 to 43 degrees Celsius reached and maintained. On the filing that carries the muscle wording, the radiofrequency warms the applicator surface to below 40 degrees Celsius. The stated purpose there is enhancing the patient's comfort during treatment.
So on the muscle side of the paperwork, the radiofrequency is a comfort feature.
The muscle indication on the NEO filing reads: improvement of abdominal tone, strengthening of the abdominal muscles, development of firmer abdomen; strengthening, toning and firming of buttocks, thighs and calves; improvement of muscle tone and firmness, for strengthening muscles in arms: That decision was issued on 6 January 2021.
Compare it with the equivalent HIFEM-only filing from 5 July 2019. It is the same sentence, three times over. The NEO's muscle clearance is not a new claim. It is the old claim on a new machine.
Two things are worth knowing about how that clearance was obtained. A 510(k) clearance is a finding that a device is much the same as one already on the market. It is not a finding that the device works, or works well, or is worth what it costs. And the January 2021 file contains no clinical testing section at all. The submission rests on electrical safety and standards testing, not on patients.
One caveat about naming clearances. BTL files with FDA under model numbers, not trade names. FDA's device records for the EmSculpt and EmSculpt NEO brand names carry no submission number at all. Matching a model number to a trade name is therefore an inference from the device description. It is not something FDA publishes. The wording quoted above is verbatim from the filings. The link between those filings and the brand on a clinic's price list is not.
In 2022 a randomised, sham-controlled trial of simultaneous radiofrequency and HIFEM was published: It is the only one.
72 people were randomised, 48 to active treatment and 24 to a sham in which the intensity was set to 5 per cent. Everyone had three abdominal treatments, one a week. Outcomes were measured by ultrasound rather than MRI.
At one month the active group's rectus abdominis was 21.5 per cent thicker, an absolute change of 2.0 plus or minus 0.8 mm. At three months it was 24.2 per cent thicker, 2.3 plus or minus 0.9 mm. Abdominal fat thickness fell 20.5 per cent at one month and 28.3 per cent at three months. The sham group showed no significant change, and the improvements were still present at six months.
Read the absolute numbers alongside the percentages: A 24 per cent increase in a muscle that was around 9 mm thick is a bit over 2 mm.
The paper carries no conflict-of-interest statement in its PubMed record. Two of its three authors declare BTL medical advisor relationships in other papers published around the same time. An independent reviewer counted this trial among seven NEO studies all written by BTL advisors. Treat it as manufacturer-affiliated evidence that happens to be the best-designed study in the field.
Everything else is open label. Nobody was blinded, and there was no comparison group except in one two-arm study. Area by area, the muscle-thickness results are:
Abdomen: 41 people, three treatments, MRI at three months: muscle 26.1 per cent thicker, with the outcome described as maintained at six months.
Buttocks: A two-arm non-randomised comparison of NEO against HIFEM alone. At three months, 27 people per arm on MRI: gluteus maximus grew 8.5 plus or minus 1.9 mm with the NEO against 5.2 plus or minus 1.1 mm with HIFEM alone, reported as 24.7 per cent against 15.9 per cent overall muscle growth.
Arms: One study. 34 enrolled, 25 imaged at three months: triceps 23.9 per cent thicker, 8.9 plus or minus 2.01 mm.
Inner thighs: 16 women, MRI at three months: muscle 23.2 per cent thicker.
Flanks: One study, oblique muscle thickness up 27.2 per cent, but the number of people treated is not stated in the abstract.
Pooled, an independent 2025 review of these seven studies puts the average muscle thickness increase at 5.5 mm. Its verdict had three parts. All seven were authored by BTL medical advisors. The measured changes were likely within the margin of error. And the photographs were frequently not standardised, showing changes in treated areas but unexplained changes in untreated areas as well.
Which of those areas are actually cleared, and for what, is on the EmSculpt NEO treatment areas page.
An earlier review by the same author covering 14 mostly HIFEM-only studies found only one with a sham group and a mean muscle thickness increase of 2.2 mm. His mechanistic objection is worth understanding rather than dismissing: muscle hypertrophy is not known to occur acutely after exercise, so an increase in measured thickness within days or weeks may be swelling rather than new muscle.
There is a small independent counterweight. A Taiwanese pilot in six people, whose authors declared no competing interests, used 3D MRI volumetry rather than a single slice. Rectus abdominis volume rose between 4.0 and 21.1 per cent at three months, but the thickness measurements were inconsistent and some decreased. That is a useful reminder that a thickness figure depends heavily on where the scanner slice was taken.
No published EmSculpt NEO study measured how much force the treated muscle could produce: The endpoint throughout is millimetres of tissue on MRI or ultrasound, sometimes converted into a percentage, sometimes accompanied by a satisfaction questionnaire.
This matters because "muscle building" implies function. A muscle that measures 2 mm thicker on a scan has not been shown to lift more. It has not been shown to hold a plank longer, or to protect a back. It has been shown to measure 2 mm thicker.
Objective strength testing does exist elsewhere in this general field — a study of a different device, using electrode-based stimulation and a dynamometer, reported measured increases in biceps and triceps force. That is a different machine with a different clearance, and its numbers do not transfer to the NEO.
The FDA's own consumer page on electronic muscle stimulators is unusually blunt. It states that no EMS devices have been cleared at this time for weight loss, girth reduction, or for obtaining "rock hard" abs, and that using these devices alone will not give you "six-pack" abs. It says these devices may be able to temporarily strengthen, tone or firm a muscle, but will not produce major appearance change without diet and exercise.
The FDA's separate page on non-invasive body contouring says the category does not treat obesity, will not result in weight loss, and does not contribute to the health benefits associated with weight loss. That framing comes from the regulator and from manufacturers' own safety documents, not from any professional society position statement.
There is also a hole in the evidence that makes the comparison with training impossible to run. A systematic review of 15 HIFEM studies found that not one of them reported patients' weight before and after treatment. Without that, a few pounds lost during a four-week study cannot be separated from anything the device did. A handful of HIFEM-only studies do report weight. They describe changes of under half a kilogram that were not statistically significant. In other words, the people studied were near a stable weight, and the results belong to that group.
Six months is where the published NEO follow-up stops: Several studies report that changes were maintained at six months. Nothing longer has been published for the NEO.
The longest follow-up anywhere in this literature is for HIFEM alone: 21 people rescanned at an average of 333 days after treatment, showing muscle thickness still 19.05 per cent above baseline. It is a single small uncontrolled study, and its own authors wrote that the finding needs to be verified by continuing follow-up and further studies.
No published study has evaluated maintenance sessions: The common clinic advice to return every three to six months is convention, not a tested schedule.
Soreness is the usual after-effect. In the FDA summary of the abdominal fat study, 11 of 42 subjects reported muscle soreness after treatment, and no adverse events were reported over the study. A separate 2026 study of a HIFEM protocol reported transient muscle soreness in 29.6 per cent of 27 participants. Comfort during treatment scored well across the FDA summaries: 92.9 per cent reported none to minimal discomfort in the abdominal study, and 19 of 29 subjects scored zero on a 0 to 10 pain scale in the thigh study.
In the FDA's post-market complaint database, six reports name EmSculpt or EmSculpt NEO, out of 31 filed for all BTL products across all years: One describes a burn with a 2 cm open skin erosion and a suspected abdominal haematoma that took about ten weeks to resolve. One describes a hard lump on each quadriceps where the applicator sat. Reporting to that database is voluntary and there is no denominator, so these counts can never be turned into a chance that something happens to you. They establish that these events have been reported at all.
BTL does not publish its instructions for use, so the manufacturer's own contraindication list for EmSculpt NEO is not publicly available. What can be said comes from the device class and from the FDA's guidance on muscle stimulators.
Tell the clinic in advance if you have an implanted electronic device. That means a pacemaker, a defibrillator, a neurostimulator or a drug pump. Say the same about any metal implant that would sit in or near the treatment field. Induced current and heating are the reason. This is a conversation to have with the team that manages the implant, not only with the clinic.
Say if you have a hernia, including a repaired one, anywhere near the area to be treated. Forced involuntary contraction over a gap in the abdominal wall is the concern. Hernia appears on FDA's list of serious risks for the non-invasive body contouring class.
Say if you have had recent surgery in the area, an active infection or broken skin there, a bleeding disorder, a seizure disorder, or a cancer being treated in the field.
Ask which of the two clearances the treatment you are being sold sits under. Muscle and fat are separate filings with separate wording, and they cover different areas.
Fever with spreading redness, warmth or pus around a treated area. These are signs of a spreading infection and need same-day urgent care, not a routine appointment.
Chest pain, palpitations or fainting during or after a session, particularly if you have any implanted cardiac device.
A blister, an open weeping area or a burn appears on treated skin
Soreness gets worse after about day three instead of settling, or does not resolve within a couple of weeks
A firm lump develops in a treated area and stays
Bruising or deep tenderness in the treated area spreads or persists
Numbness or altered sensation in the area does not settle
You were told to expect a specific percentage of muscle growth and want to see which study that number came from