The Slendertone ab toner belt plopped onto my radar when a reader of my popular Ab Wave review left a comment asking me if I’d ever heard of it.
I hadn’t heard of this specific brand, but I was well aware of the different types of electrostim products.
I did a bit of digging and found the company website company website and a listing on Amazon with numerous consumer reviews.
In a promotional video for the product, the announcer asks, “Do you want firmer, toned abs in just weeks? Then you need the button, the Slendertone button.”
Then the ad goes straight into a parade of hot-bodied goddesses and adonises which gives viewers the misleading impression they can put on the belt, push a button, and get the same svelte bodies as the models.
I’ll be honest. I think the advertising for this product is complete rubbish and it sends the wrong message to consumers.
There are already so many ab gadgets and gimmicks out there that my knee jerk reaction was to throw the baby out with the bathwater and give Slendertone a good smack across the face with a frozen Atlantic salmon.
The company claims it’s “clinically proven,” which is often a red flag for snake oil.
Surprisingly, the company actually cites a single peer-reviewed journal article as evidence of product efficacy. Sounds great, but in my opinion, I think they took some liberties with lifting their advertising claims out of context.
Therefore, the purpose of this article is to:
- Provide an independent review of Slendertone marketing claims; and
- Compare them to the original research
Also check out this site’s health and nutrition calculators:
- Macronutrient percentage calculator
- Protein calculator for weight loss
- Total daily energy expenditure calculator
- Lean body mass calculator
What is the Slendertone Flex Pro?
Before we dismantle and evaluate the evidence, what exactly is the Slendertone Flex?
Made by Bio-Medical Research Ltd and headquartered in Galway, Ireland, the product line encompasses electrical muscle stimulation pads which are applied to the skin and ‘zap’ your muscles to contract.
Electrostimulation has therapeutic use in a clinical environment (hospital or clinic) for rehabilitation purposes, but this technology is now being applied to consumer health, fitness, and beauty goods (such as Slendertone).
Does it really work?
The short answer is yes, no, and it depends. You need to define “work” and what it means to you.
This question begets two more questions which are necessary to consider in answering the overall question:
- Is there any objective, scientific, peer-reviewed evidence to support marketing claims? and;
- What are your individual expectations from the product?
Question 1: Are claims supported by science?
A single study is listed on the company’s website. Porcari and colleagues (2005) compared a group of men and women receiving 8 weeks of abdominal electrostimulation to a non-electrostim control group.
At follow up, they noted the following results:
- 58% increase in strength
- 100% abdominal endurance, but 28% increase in control group due to learning effect. Therefore they subtracted the 28% from 100% for a 72% change.
- 2.6 cm decrease in abdominal circumference
- 3.6 cm decrease in waist circumference
- 1.4 cm decrease in front to back diameter
- No change in abdominal or suprailiac skinfold thickness
I compared the marketing claims against the original research article and I can verify that the numbers are “technically” truthful, BUT…
There are a number of limitations you must consider:
Strictly using the machine, the increases in strength and endurance would be isolated to the specific targeted areas.
For any kind of functional/translational benefit to real world sports or activities, you would actually need to do full body compound movements which fire the abdominal musculature within the context of the entire kinematic chain (using all the body’s muscles together the way they were designed).
For example, if you are a baseball pitcher, you would need well-conditioned core musculature to link your lower and upper body during a pitch.
This would best be trained by both sport-specific exercise (pitching a baseball) or simulated whole body movements which mimic pitching technique (cables).
Bottom line: the machine is highly unlikely to give you a body that looks anything like the hired models in their advertisements.
There were improvements in circumference measures but in discussing the limitations of the study, the authors openly acknowledge:
“An increase in the strength of the abdominal muscles could theoretically reduce the circumference of the mid-section. Since, one of the roles of the abdominal musculature is to support the abdominal contents, it follows that strengthening the abdominal muscles could in effect “pull in” the abdomen, much like a girdle. This effect would decrease both the circumference and front-to-back diameter of the waist.”
Plain English translation: the numbers reported are “truthful” but there may be other reasons to explain the results that have nothing to do with changes in body fat.
The results also indicated no change in abdominal and suprailiac (just above your hipbone) skinfold thicknesses, body weight, or body mass index.
My interpretation is that, whilst there were changes in the tape measure readings, when put into context with these other factors, we really don’t have a physiologically confirmed reason WHY the circumference measures decreased.
There was no direct measure of visceral (around the organs) or subcutaneous (superficial fat you can pinch) fat changes.
Circumference readings and skinfold calipers can be useful field measures and give suggestive evidence, but are not the gold standard of body composition – not even close.
I would like to see a more thorough investigation using sensitive body composition assessment measures such as CT scans, MRIs, or DEXA to assess body composition.
The study’s authors also state:
“In support of the decrease in waist circumference was the fact that 13 out of 24 (54%) subjects in the stimulation group felt that their cloths fit better around the mid-section at the conclusion of the study. None of the control group subjects reported any change in how their clothes fit.”
The issue with the above statement is that how one’s clothes fit cannot be reliably or objectively measured. So whilst this might be suggestive, it does not necessarily indicate a reduction in fat localised to the belly.
Taken as a whole, the results from this study demonstrate that localised electrostimulation causes small increases in isolated strength and endurance in a clinical setting.
However, from a practical real-world standpoint, I would not recommend Slendertone as a solution for reducing body fat or body weight.
You can do all the crunches or electrostimulation you want, but your abs will NOT become visible until you lose the fat between your skin and muscles. Less doughnuts and hamburgers and more fruits and veggies!
An earlier electrostimulation study by Porcari and colleagues (2002) found no significant improvements in measurements of body weight, body fat (via skinfolds), girth, isometric and isokinetic strength (biceps, triceps, quadriceps, hamstrings), and appearance (via photographs from the front, side, and back). However, I believe this study used a different electrostimulation unit and the subjects used the machine only three times per week.
Question 2: What are your expectations?
Whether the Slendertone belt “works” or not depends on your individual expectations.
Will it make your abdominal muscles stronger? Technically yes.
It could plausibly increase localised muscular strength and endurance around your mid-section, but it’s not any kind of relevant functional training that will translate to making you a pro athlete.
It will not translate to any sport-specific adaptations. For that, you’ll need to get out and actually do sport and exercise (the real stuff!).
Will it help you strip away that loaf of fat around your belly? Highly unlikely.
As I previously mentioned, if you think this product is going to strip away the fat while you kick back on the couch downing chips and beer, then you’re in for a surprise. The evidence does not support this.
The fine print – always read the fine print
As with all exercise products and supplements which give the impression you can get in shape while you lounge around the house, you must ALWAYS read the fine print (the one with the pesky *asterisk*).
The company discloses on their website:
“ *Slendertone ab belts must be used as per the guidelines stated in the instruction manual. For best results, we recommend that you use your Slendertone belt in conjunction with a normal, healthy diet and exercise.”
I interpret this to mean that the Slendertone belt itself probably won’t do much to reduce body fat unless you help it along with some veggies, tofu, hitting the gym, plus some regular walks around the neighbourhood.
How much does it cost?
Slendertone can range from $80 to $180 USD depending on the model and whether or not it’s new or used.
Depending on your individual budget, that’s a fair bit of cash to spend on something backed by a single study loaded with limitations.
Where is it available?
The company website lists distributors in numerous countries including the United Kingdom, Ireland, United States, Australia, New Zealand, Hong Kong, Macau, Japan, Korea, Philippines, Singapore, Malaysia, Indonesia, Taiwan, even Russia. On the top right hand side of the websites, you’ll see a drop-down menu for a number of countries.
Risks or side effects
In my experience with electrostim in general and in my investigation of this particular product, I did not come across any documented risks or dangers associated with using the Slendertone as instructed.
However, one unlucky woman did file a complaint with the Food and Drug Administration when her Slendertone unit exploded.
I’m renowned for pissing on the parade with my scathing reviews, but compared to other ab gadgets on the market, I found the Slendertone marketing claims to be comparatively tame (as I did with It Works body wraps).
Bio-Medical Research Ltd has not made any overtly false claims in their promotional materials, but with lots of sleek bodies and testimonials plastered all over the website, I think you need to be aware of how you personally react to and interpret these messages.
Be careful not to mislead yourself into thinking the product will burn fat off your abs with no effort. That’s highly unlikely to happen.
At a cost of a couple hundred bucks, I suggest that you determine what you want to get out of this product, look at the existing evidence and its limitations, and then make an informed decision about whether or not it’s right for you.
Tuesday 23rd of November 2021
This is an old blog that I just ran into, so hope you still respond. I have diastasis, rectus abdominis (male) per an ultrasound I just had. I am losing weight now that I have a healthy diet. I also exercise regularly, to include full ROM of all muscle groups. The abdominal bulging during exercise really worries me (that's why my doc ordered the ultrasound). Do you think this device would benefit me and help close the gap (4 cms) between my ab muscles?
Dr Bill Sukala
Wednesday 24th of November 2021
Hi Keith, It's hard to say for sure, but I would strongly suggest working closely with your doc and perhaps getting a referral to work with a physical therapist who can best prescribe exercises specific to your situation.
Friday 11th of January 2019
Hi there. My question is....would the electrical stimulation of Abs muscles impact in any way on a Titanium Hip Replacement joint as it is metal? Thank you.
Sunday 7th of April 2019
Hello, I was wondering if this devise can be used if you have a pacemaker/defibrillator internal devise? Thank you
Dr Bill Sukala
Friday 11th of January 2019
I'm not sure what you mean. Impact in what way? I doubt it would adversely affect the hip joint in any way, but if you have concerns, it's always best to ask your doctor, as s/he will be most familiar with your medical history.
Sunday 2nd of September 2018
Hello there, great blog and research. I am using the slendertone belt as I type. I find it works and it motivates me to work out in the gym; but I am fairly slender and not over-weight. I do work out in the gym and use the slendertone when Im on the laptop or watching TV. Its useful but it is a strengthening device not a slimming tool.
Thursday 7th of June 2018
Hi there - I just read every message in this thread as not to repeat a question. I have had great success with this belt. I set it to the point where it is slightly uncomfortable. It automatically sets the time to increase after each week of usage. My lower back is such that crunches are difficult for me to do, so this has really helped me strengthen my core. This product has encouraged me to exercise more. I am at the point where I can hold planks for longer than ever before now! I used to give up after 30 seconds. To me, this is worth the cost. Just committing to this machine is making me more aware of my abs, posture, back and thinking every day about what I am doing to improve my body.
My question is that i wonder if I could wear it across my back? I want to try it, but don't know if the placement of the electrodes might not be properly aligned and I could tweak it. Thanks in advance for you time and consideration.
Dr Bill Sukala
Thursday 7th of June 2018
Hi Kathryn, The thing to remember with these types of devices is that they work muscles in isolation. Your core/postural muscles tend to work best together rather than by themselves and, accordingly, it's a good idea to train the muscles of the body in ways that are consistent with our natural movement patterns. You could probably put the device anywhere on the body and, as I mentioned in my article, these sorts of gadgets can help in situations where you're immobilised (like after injury, surgery, etc), but they're not substitutes for real, natural human movement in healthy adults. Kind regards, Bill
Wednesday 30th of May 2018
Hi Dr Bill,
I've a 22mm stone in right kidney. Please advise ..is it OK to use this slender tone ab belt or any other electronic stimulator to reduce the weight?
Dr Bill Sukala
Wednesday 30th of May 2018
That's a question only your doctor can answer. If your doc clears you then you should be ok. Kind regards, Bill