From Synthol and silicone injections to the new world of injectable muscle contouring
Written by Injector Rick at BONAVADA Aesthetics in Worthing
Apparently, the latest route to a more muscular body may not involve meal preparation, protein shakes or spending six evenings a week arguing with a cable machine.
It may involve a cannula, several large syringes of filler and a bank card with very relaxed spending limits.
Videos are now appearing online and across social media showing hyaluronic acid fillers and biostimulators being used to exaggerate the appearance of pectoral, abdominal, shoulder and arm muscles.
The results can look impressive.
But are we genuinely looking at the future of body contouring, or are we repeating an old pattern with newer and more sophisticated products?
The straightforward answer
Injectable muscle contouring can create the appearance of greater muscular definition.
It does not grow muscle, increase strength or improve genuine muscle tone.
The filler is generally placed into the tissue overlying the muscle, creating additional projection and stronger areas of light and shadow. In simple terms, it enhances the outline of the muscle underneath.
It is contouring, not bodybuilding.
What does the current research show?
The science exists, but it remains very small.
A 2024 pilot report described treatment of ten men using hyaluronic acid around the abdominal and pectoral areas. An average of 42 ml was used, with follow-up extending to 120 days. The authors reported high satisfaction and no serious adverse events, but acknowledged that longer-term research was needed (Dziabas, Kasai and Viana, 2024).
A separate study followed seven men after ultrasound-guided abdominal filler treatment. All reported improvement, and residual hyaluronic acid remained visible on ultrasound after nine months. Reported effects included mild bruising and short-lived discomfort (Lourenço et al., 2025).
Then came a 2025 case report involving one man who received a rather breathtaking 134 ml of filler across his chest, shoulders and arms. The visible result was positive and no complication was reported after one month (Yi et al., 2025).
That proves the technique can change appearance.
It does not tell us what happens after repeated treatments over five, ten or twenty years.
Why does this feel strangely familiar?
Bodybuilders have previously injected site-enhancement oils, commonly referred to as Synthol, directly into muscles to make them appear larger without creating real muscular growth.
The complications reported from these oils include infection, deformity, chronic inflammation, severe fibrosis and impaired muscle function. Some cases have required extensive surgical removal of damaged tissue (Nassar et al., 2024).
There is also the history of free liquid silicone injections.
During the twentieth century, silicone was injected directly into breasts and other body areas to create volume without implants. It sometimes looked successful initially. Years later, some patients developed migration, painful nodules, granulomas, chronic inflammation and tissue destruction. In one published case, complications eventually required bilateral mastectomy 15 years after the original injections (Bhardwaj et al., 2020).
The US Food and Drug Administration continues to warn that injected free silicone can migrate and cause permanent disfigurement, embolism, stroke or death.
Is modern HA muscle contouring the new Synthol?
No. That comparison would be scientifically unfair.
Modern hyaluronic acid filler is fundamentally different:
it is biodegradable;
it is manufactured as a medical product;
it can often be reduced using hyaluronidase;
and published muscle-contouring techniques generally place it over the muscle rather than injecting oil directly into it.
Hyaluronic acid is not Synthol, and it is not free silicone.
The valid comparison is about timing.
In each case, the impressive immediate result arrived before we fully understood how large quantities of injected material would behave over many years.
History does not prove that the same disaster will happen again.
It does remind us that a satisfied patient after one month is not long-term safety data.
Could the filler migrate?
Migration is a recognised potential complication of dermal fillers generally, but we do not yet know how frequently it might occur following high-volume muscle contouring.
The chest, abdomen and arms are constantly moving, stretching and being compressed. Researchers have not yet established how repeated muscular movement, exercise, pressure and maintenance treatments affect the material over several years.
The FDA also notes that migration, permanent nodules and delayed reactions can occur with dermal fillers and that the safety of repeated long-term use has not been evaluated in controlled clinical studies.
That does not mean migration is inevitable.
It means the honest answer is currently:
We do not know enough yet.
What about biostimulators and “enzymes”?
This introduces another level of uncertainty.
Hyaluronic acid can usually be treated with hyaluronidase. Common collagen biostimulators work differently and cannot necessarily be dissolved in the same straightforward way.
If HA, biostimulators and vaguely described “enzymes” are combined, a future lump or irregularity may be harder to interpret. Is it filler, collagen, inflammation, infection or several things at once?
Without knowing the exact products, quantities and tissue planes used, a branded protocol name tells us very little about its long-term safety.
My honest verdict
Injectable muscle contouring is not ridiculous. It has a believable mechanism, some impressive early results and possible value for correcting asymmetry following injury, surgery or uneven muscle development.
But its popularity is moving considerably faster than its evidence.
The current studies involve very small numbers of patients, large product volumes and limited follow-up. They cannot yet reliably establish rates of migration, nodules, repeated-treatment complications or problems that might appear many years later.
At the time of writing, this is not currently a treatment I offer at BONAVADA Aesthetics.
Yet.
I am interested, but not convinced. Never say never, although the long-term evidence gets a vote before I start ordering body filler by the bucket.
Frequently asked questions
Can filler genuinely give you a six-pack?
It can make the abdominal contours appear more prominent. It does not create muscle fibres, reduce body fat or improve strength.
Is it the same as Synthol?
No. HA filler is biodegradable and is generally placed over the muscle. Synthol is a non-biodegradable site-enhancement oil injected into muscle.
Is injectable muscle contouring proven to be safe?
Small early studies are encouraging, but there is not yet enough long-term research to establish its safety over repeated treatments and many years.
The bottom line
Modern HA filler is not free silicone or bodybuilding oil.
But history repeatedly teaches us the same lesson:
An excellent photograph today cannot tell us what an injected material will be doing inside the body ten years from now.
Written by Injector Rick at BONAVADA Aesthetics, Worthing.
Because apparently even a six-pack can now arrive by syringe.
References
Bhardwaj, P., Greenwalt, I., Ko, K., Sher, S.R. and Tsiapali, E. (2020) ‘Free silicone injections to the breast: Delayed complications and surgical management of sequelae’, Plastic and Reconstructive Surgery Global Open, 8(11), e3208. doi: 10.1097/GOX.0000000000003208. Available at:
https://pmc.ncbi.nlm.nih.gov/articles/PMC7722574
Accessed 30 July 2026
Dziabas, D., Kasai, M. and Viana, R. (2024) ‘Corporal Filler HD, a minimally invasive technique for male body contouring: A pilot study’, Plastic and Reconstructive Surgery Global Open, 12(11), e6269. doi: 10.1097/GOX.0000000000006269. Available at:
https://pmc.ncbi.nlm.nih.gov/articles/PMC11557006
Accessed 30 July 2026
Lourenço, L.M., Di Sessa, D., Tebet, A.C.F., de Noronha, M.G.O., de Medeiros, H.L. and Sigrist, R. (2025) ‘Hyaluronic High Definition Fill Technique’, Journal of Cosmetic Dermatology, 24(2), e16692. doi: 10.1111/jocd.16692. Available at:
https://pmc.ncbi.nlm.nih.gov/articles/PMC11845964
Accessed 30 July 2026
Nassar, A., Osseis, M., Sleilati, F., Nasr, M. and Abou Zeid, S. (2024) ‘Management of Synthol-induced fibrosis’, Plastic and Reconstructive Surgery Global Open, 12(12), e6391. doi: 10.1097/GOX.0000000000006391. Available at:
https://pmc.ncbi.nlm.nih.gov/articles/PMC11649267
Accessed 30 July 2026
United States Food and Drug Administration (FDA) (2017) FDA warns about illegal use of injectable silicone for body contouring and associated health risks. Available at:
Accessed 30 July 2026
Yi, K.H., Wan, J., Yoon, S.E., Basmage, L. and Bautzer, C. (2025) ‘Hyaluronic acid filler injection for upper body aesthetic contouring’, JPRAS Open, 45, pp. 443-448. doi: 10.1016/j.jpra.2025.07.006. Available at:
https://pmc.ncbi.nlm.nih.gov/articles/PMC12396288
Accessed 30 July 2026