A small upper-arm MRI study reported reduced local fat thickness and increased triceps thickness after four HIFEM-plus-RF sessions; it did not establish a specific degree of skin tightening or strength gain.
How to interpret the measured result
The MRI observations concern upper-arm muscle and fat. They do not establish a skin-tightening effect or equivalence to an arm-lift operation.
Study at a glance
Design: Uncontrolled upper-arm MRI study.
Participants: 34 enrolled; MRI n=28 at one month and n=25 at three months.
Research protocol: Four bilateral 30-minute HIFEM+RF sessions.
Follow-up: One and three months.
Evidence visual: Which upper-arm outcome was actually measured?
The sections below distinguish the measured outcomes from questions the study cannot directly answer.
Fat layer
One month, n=28: -22.3 % thickness change; Three months, n=25: -25.5 % thickness change.
Local MRI fat-layer measurements. Three-month absolute reduction: 4.9 mm.
Triceps
One month, n=28: 21.5 % measurement increase; Three months, n=25: 23.9 % measurement increase.
Three-month absolute increase: 8.9 mm. Not an outcome for every upper-arm muscle.
Skin or strength?
A defined skin-tightening effect, biceps response or percentage strength gain cannot be derived from these MRI results.
Source for the visual: [S05]. No concurrent sham or exercise comparator. Group averages do not identify an individual’s ideal course.
First identify what an “arm concern” means
People use the same phrase, “I want to improve my arms”, to describe very different concerns. One person means local fat, another means muscle definition, and another is primarily bothered by loose skin. These are different treatment questions.
The upper-arm study by Jacob and Weiss is most useful when read as evidence about fat and muscle measurements. It should not be used as though it were a direct study of removing excess skin or restoring every aspect of arm function. [S05]
This distinction makes the consultation more useful from the start. Before discussing a course, identify which tissue or functional issue is actually driving the concern.
For treatment background, read What is EMSCULPT NEO?. This article focuses on the specific research question.
How the study was organised
Thirty-four participants were enrolled and received four bilateral, 30-minute upper-arm treatments combining HIFEM with synchronised RF. MRI was used to measure the local fat layer and triceps region. Twenty-eight participants attended the one-month MRI assessment and 25 completed the three-month assessment. [S05]
The study did not include a concurrent sham or exercise comparison group. Its contribution is the documentation of what happened to the measured tissues after the study protocol, rather than proof of superiority to other approaches.
The reported MRI findings
At one month, average fat thickness had decreased by 22.3%, or 4.0 mm, while the reported muscle increase was 21.5%, or 8.2 mm. At three months, local fat thickness was 25.5% lower, or 4.9 mm, and the triceps measurement was 23.9% greater, or 8.9 mm. [S05]
The absolute measurements help explain the percentages, but neither is a prediction for a new patient. The three-month result comes from 25 participants, not all 34 originally enrolled.
The accompanying visual presents the fat and muscle findings separately and shows the outcomes that were not established by these measurements. That is more useful than collapsing the paper into a general statement that “arms improved by 25%”.
Why this is not a loose-skin study
A thinner layer of fat and a larger muscle measurement do not automatically establish a particular improvement in skin laxity. Excess skin is its own concern. An intervention can affect tissues beneath the skin without demonstrating the amount of skin tightening a patient expects.
The arm MRI paper does not justify a promise that hanging skin will disappear. It also does not establish equivalence to an operation designed to remove skin. Those are different questions and different outcomes.
At an assessment, ask the clinician to explain what proportion of the visible concern appears related to fat, muscle contour or skin. A clear answer may be more valuable than a larger treatment package based on a loosely defined goal.
Triceps evidence is not automatically biceps evidence
The paper's arm findings should retain their anatomical label. A triceps measurement does not become a biceps result simply because both muscles are in the upper arm. [S05]
Likewise, an increase in measured muscle thickness is not the same as a measured improvement in grip strength, elbow function or athletic performance. Those outcomes need appropriate testing rather than an assumption based on imaging.
This is especially important when someone is recovering from injury, managing pain or hoping to resume exercise after surgery. The cosmetic imaging protocol does not provide individual rehabilitation clearance. A clinician needs to assess the underlying condition and relevant restrictions separately.
What a useful review would look like
Before treatment, agree on the problem being addressed and how it will be documented. For appearance, standardised photographs can help; for circumference, use the same landmarks; for a functional concern, use a suitable functional assessment.
Avoid comparing a relaxed arm in one photograph with a flexed arm in another and presenting the difference as evidence of tissue change. The purpose of consistent documentation is to make the review honest enough to guide a decision.
It is also useful to state in advance what will happen if the main concern is unchanged. Reassessment may mean adjusting the plan, considering another option or deciding that no additional treatment is worthwhile. The published averages should not be used to explain away an individual's lack of meaningful benefit.
Timing and expectations
The study's larger average changes were reported at three months compared with the earlier visit. That is an observed pattern in this cohort, not a schedule that every person's result must follow. [S05]
A treatment plan should therefore include a sensible review period without promising a fixed date when the arms will look a certain way. Maintenance cannot be prescribed solely from a study that highlighted short-term follow-up.
The same applies to the number of sessions. Four sessions describe what the researchers studied. They do not establish that four is the minimum, maximum or optimal course for every person and every upper-arm concern.
Safety, disclosure and the ¹EM takeaway
The study reported favourable treatment comfort and no serious safety signal in its small cohort. Nonetheless, RF can cause thermal injury and magnetic stimulation requires screening for relevant implants and other contraindications. A published average comfort score does not mean every treatment is pain-free. [S05, G01]
The article declared no funding or relevant conflicts. That is the authors' disclosure statement, not a separate audit of every possible commercial connection.
The ¹EM interpretation is specific: there is published MRI evidence of upper-arm fat and triceps changes after the studied combined protocol. The right next step is to establish whether those are the outcomes that matter for your arms, rather than assuming the same paper answers questions about skin excess or rehabilitation.
Frequently asked questions
How many people were included in the upper-arm result?
Thirty-four were enrolled, 28 attended one-month MRI and 25 completed the three-month MRI assessment. The three-month percentages should be linked to the 25-person follow-up group. [S05]
What were the three-month results?
The paper reported a 25.5% average reduction in local fat thickness and a 23.9% increase in the triceps measurement, corresponding to 4.9 mm and 8.9 mm respectively. These are group imaging findings. [S05]
Will this remove loose arm skin?
The study does not establish a defined skin-tightening or skin-removal result. Loose skin should be assessed as a separate concern rather than inferred from fat and muscle measurements. [S05]
Can the triceps result be used to advertise biceps growth?
Not from this paper. The anatomical site and measured muscle should remain attached to the finding. A different placement needs its own supporting evidence and clinical assessment.
Is four sessions the correct course for me?
Four sessions were used in the research protocol. The article cannot decide the appropriate treatment plan, settings or suitability for an individual.
Sources
[S05] Jacob C, Weiss RA. Simultaneous HIFEM and Synchronized RF Procedure Can Be Effectively Used for Increasing Muscle Mass and Decreasing Fat in the Upper Arm. Journal of Clinical and Aesthetic Dermatology. 16(2):50–54. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC10005810/
[G01] US Food and Drug Administration. Non-Invasive Body Contouring Technologies. Patient information. 2026. https://www.fda.gov/medical-devices/aesthetic-cosmetic-devices/non-invasive-body-contouring-technologies
Practical information
Start with an individual assessment
General information cannot determine whether treatment is right for you. Request a private assessment with the ¹EM team.
General educational information, not individual medical advice. Published research findings are not ¹EM patient-outcome data. Suitability, experience and results vary.