Muscle electrostimulation is experiencing a resurgence of interest in the worlds of training and rehabilitation. For some, it is a useful rehabilitation tool, while for others, it is an almost magical way to replace more traditional training. In the consumer fitness marketing space, electrostimulation is often presented as a quick method to lose fat, tone the body, or get results in just a few minutes per week.
As you might suspect, the reality is more nuanced…
Electrostimulation can effectively induce muscle contractions and lead to certain adaptations. In some contexts, it can improve muscle strength, help preserve muscle mass, or complement a more traditional training program. However, it does not automatically replicate the effects of a full workout, and unfortunately, the promises regarding weight loss or “targeted fat burning” are often exaggerated.
Let’s look in more detail at where electrostimulation comes from, what it is, and what it actually does…
What are the origins of electrostimulation?
If we look at the scientific origins of electrostimulation, they likely date back to the 18th century, with Luigi Galvani’s work on animal electricity. In 1791, Galvani published De viribus electricitatis in motu musculari commentarius1, a foundational text showing that an electrical stimulus can cause a muscle to contract. In the 19th century, the work of Duchenne de Boulogne played a major role in the development of electrical stimulation applied to human muscle, notably with De l’électrisation localisée et de son application à la pathologie et à la thérapeutique2, published in 1861. This work helped structure the use of electrostimulation in neurology and in the functional exploration of movement. In contrast, the use of electrostimulation as a training method is much more recent. This approach developed primarily in the 20th century and gained momentum starting in the 1970s–1980s in physical preparation, rehabilitation, and later in fitness training. Although the idea of using electricity to make a muscle contract is ancient, its modern use as a structured training tool is relatively recent in the history of physiology.
What is electrostimulation?
Electrostimulation consists of applying an electrical current through the skin to stimulate a motor nerve and induce muscle contraction. In practice, electrodes are placed on the skin over a muscle or muscle group, and an device delivers electrical impulses according to defined parameters: frequency, pulse duration, intensity, contraction time, and rest time3,4. There are different forms of electrostimulation, each with its own applications and effects (and, above all, they should not be confused).
EMS or NMES
EMS (Electrical Muscle Stimulation), also called NMES (Neuromuscular Electrical Stimulation) in the scientific literature, is a form of electrostimulation that uses electrical impulses delivered through the skin to activate motor nerves and induce involuntary muscle contraction. It is used in rehabilitation to limit atrophy or restore muscle function, but also as a training complement to stimulate muscle strength when voluntary contraction is limited. The main application parameters are stimulation frequency, pulse duration, current intensity, contraction time, and rest time.
In practice, overload relies primarily on the progressive increase of the intensity tolerated by the participant, as this largely determines the level of muscle tension achieved. Overall, data suggests that EMS can primarily improve muscle strength, especially when applied at a high intensity and integrated into a structured program. Its effects strongly depend on the context of use, the targeted muscle, and whether or not it is associated with voluntary contraction or dynamic exercise3-5.
WB-EMS
WB-EMS (Whole-Body Electromyostimulation) is a form of electrostimulation in which several large muscle groups are stimulated simultaneously via a vest, a belt, and straps or electrodes placed on different regions of the body, generally during the execution of simple movements or low-load exercises. Unlike local EMS, which targets a specific muscle or muscle group, WB-EMS aims for global body stimulation. Its application parameters are similar to EMS (stimulation frequency, pulse duration, intensity tolerated by the participant, etc.), with the added complexity of the exercises or movements performed during the session. Available data suggests that WB-EMS can improve muscle strength and, in some cases, certain body composition parameters, particularly in non-athletic, sedentary, or older adults. The observed effects remain highly dependent on the protocol, the population studied, and the supervision6,7. Furthermore, this modality must be used with caution, as excessive intensities or inadequate progression have already been associated with significant adverse effects, particularly muscular ones8.
TENS
TENS (Transcutaneous Electrical Nerve Stimulation) is a form of electrostimulation applied through the skin primarily for analgesic purposes, not to provoke significant muscle contraction like EMS/NMES. It consists of stimulating mainly sensory nerve fibers using skin electrodes to modulate pain perception9. Its application parameters are generally similar to EMS. However, unlike EMS, it is not a modality based on a logic of progressive muscular overload. TENS is mainly used for the symptomatic relief of pain in acute or chronic contexts, with variable results depending on the indication, the protocol, and the individuals. It can therefore be useful as a complementary non-pharmacological tool, but it does not aim for strength development or structural muscle adaptation10,11.
How does electrostimulation work?
During a voluntary contraction, the brain sends a bioelectrical signal to the motor neurons that activate the muscle fibers. With electrostimulation, this central command is partially bypassed: the external current stimulates the peripheral nerves and causes contraction in an artificial or “external” way3,7,11.
Voluntary contraction vs. electrostimulation
In a voluntary contraction, the motor units that mobilize muscle fibers are generally recruited in a progressive order (Henneman’s Principle12), from the smallest to the largest (Type 1 to Type 2). With electrostimulation, recruitment is more dependent on electrode placement, tissue depth, and current intensity. The recruitment of motor units and muscle fibers is therefore more “geographical” or based on the proximity of the current to the motor units. This changes the way the muscle produces force and partly explains why an electrical contraction is not equivalent to a well-coordinated voluntary movement4. This proximity effect modifies the application of Henneman’s principle by potentially changing the order of muscle fiber recruitment. During a voluntary muscle contraction, we observe a progressive recruitment of motor units (Type 1 to Type 2) based on the required intensity. The heavier the load, the more 1) a large quantity of motor units and muscle fibers are involved and 2) there is recruitment mobilizing Type 2 units. However, during muscle contractions induced by electrostimulation, the motor units and fibers located near the current emission are the ones mobilized, regardless of their nature (Type 1 or Type 2). One thus ends up bypassing Henneman’s principle.
Adaptations
Electrostimulation can induce:
- Strong local muscle tension
- Significant local fatigue
- Mainly peripheral neural adaptations
- In some cases, strength gains
- Sometimes effects on muscle mass or body composition.
The probably most critical point lies in the participant’s ability to tolerate the pain generated by the current. In practice, many users do not reach a sufficient intensity to produce a significant training stimulus allowing for major adaptations4,13. The intensity in electrostimulation is limited by pain tolerance rather than effort tolerance.
The main ways to use electrostimulation
We can distinguish three main contexts for using this form of training/stimulation.
Electrostimulation alone Here, the device causes contractions while the person remains at rest or performs little voluntary movement. This approach is primarily relevant in rehabilitation, in cases of immobilization, pain, or significant weakness4,5,7. For example, a person immobilized following a trauma where one would wish to preserve muscle mass and limit atrophy, but who is unable to voluntarily contract certain muscles.
Electrostimulation combined with voluntary contractions In this case, the person voluntarily contracts the muscle while the device stimulates at the same time. This approach seeks to increase the level of muscle activation and improve the transfer to more functional muscle capabilities4,5,7. Following underutilization or an injury, one can locally stimulate a muscle contributing to a complex movement to avoid muscle compensations by other involved muscles.
Electrostimulation combined with loaded exercises Here, electrostimulation is added to exercises such as squats, lunges, or other strength training movements. This is notably the case for some WB-EMS approaches used in the fitness industry. This method adds electrical stimulation to voluntary mechanical work. This is probably the most relevant form when one is interested in performance or body composition in healthy adults4,5,7,8,14.
What are the effects on muscle strength?
Systematic reviews and synthesis work show that NMES/EMS can improve muscle strength, particularly in the quadriceps, especially when contractions are sufficiently intense and the program lasts for several weeks4,14-17.
However, nothing is miraculous…
It is important to qualify certain elements. For example, strength gains are more marked in deconditioned, injured, immobilized, or older people. In already-trained subjects, effects are sometimes observable, sometimes absent.
EMS alone can improve the strength of a muscle for a simple specific movement (leg extension), but that does not mean it improves a complex movement as much as traditional strength training. Electrostimulation can hardly coordinate and adequately optimally engage several muscles involved in a complex movement like a squat.
Although electrostimulation can increase strength, it does not automatically replace a well-structured strength training program.
What are the effects on power?
Muscle power corresponds to the ability to produce force quickly. It is a more specific quality than maximum strength because it also depends on speed, coordination, and the movement performed.
Some studies in athletes have reported positive effects of electrostimulation on variables such as jumping or certain neuromuscular performance markers, but the results are more variable than for strength18.
Power is not strictly a question of contracting harder. Power production depends on many factors (synchronism and multi-muscle coordination among others) that allow for optimal management of the contribution of several muscles to the same movement. Being able to produce force quickly, without opposition from other muscles, in a specific movement represents a significant work of recruitment and muscle synchronism. However, EMS reproduces poorly the coordination requirements of a jump, a sprint, or a sports movement by combining all the required variables.
In practice, electrostimulation can therefore be seen as a potential complement, but rarely as the core of power training.
What are the effects on local muscle endurance?
Local muscle endurance corresponds to the capacity of a muscle to maintain an effort or repeat contractions over time. Here again, electrostimulation can produce local adaptations, notably when a protocol repeats a large number of contractions4,5,14.
However, if one stimulates a muscle in a laboratory, one can sometimes improve its local resistance to fatigue, but this does not guarantee an equivalent improvement in functional tasks. Furthermore, pain tolerance becomes a moderating element that can limit the prolonged use of electrostimulation at intensities likely to promote adaptations in local muscle endurance.
What are the effects on aerobic capacity and aerobic endurance?
Here, commercial promises often exceed real data.
Aerobic capacity Aerobic capacity, or maximal oxygen consumption (VO2max), depends on the integration of the cardiovascular, respiratory, and muscular systems. Electrostimulation certainly causes local muscle work, but it does not spontaneously replicate all the constraints of a structured aerobic training. One targets the periphery (the muscle), but one manages less to reach the more central elements (cardiovascular component).
In healthy people capable of walking, running, pedaling, or rowing, there is no reason to consider EMS as a primary tool to improve aerobic capacity. In contrast, in clinical or very deconditioned populations, NMES can contribute to maintaining or improving certain functional indicators when conventional exercise is difficult19. Using electrostimulation as a reconditioning tool acting as a gateway to more conventional aerobic activities could prove to be an interesting strategy when physical capabilities are very limited.
Aerobic endurance Aerobic endurance, i.e., the capacity to sustain a prolonged effort, relies even more on training specificity. To improve this quality, one must generally expose the body to a prolonged effort mobilizing a large muscle mass and sufficient cardiovascular load.
EMS can eventually improve certain peripheral determinants, such as local muscle function. But it does not constitute an effective substitute for classic cardiovascular training in people capable of doing so.
What are the effects on body composition?
This is one of the most popular topics, but also one of the most distorted by marketing.
Literature on WB-EMS suggests that there may be, in certain non-athletic populations, modest positive effects on lean mass, strength, and certain body composition parameters20. But these effects should not be interpreted as proof that EMS melts fat or allows for significant weight loss without lifestyle changes.
What the data allows us to say
- WB-EMS protocols can contribute to improving body composition in non-athletic adults, especially when they increase the overall activity level or serve as a gateway to more regular practice20.
- The observed effect is not comparable to the extreme promises of certain marketing messages.
- There is no solid basis for claiming that a device will target fat locally.
- Fat mass loss depends primarily on energy balance, diet, total physical activity level, and the functional maintenance of muscle mass. It can also prove difficult to significantly increase energy expenditure during electrostimulation sessions without generating significant/excessive fatigue that could affect the ability to expend energy over 24h.
- The FDA has also recalled that muscle stimulators are sometimes promoted abusively with claims related to weight loss, waist reduction, or obtaining dream abs, without a solid basis to justify such promises21.
What about energy expenditure?
This is an essential question, notably because it directly touches on the principle of energy balance related to weight loss. To fully understand the energy expenditure related to electrostimulation training, one must go through a little physiology. Muscle fiber energy expenditure depends primarily on the activity of the links between actin and myosin filaments and the activity of the calcium pumps necessary for muscle contraction. Type 1 motor units and their associated muscle fibers (also Type 1) are the most efficient. To generate tension, these motor units and fibers are the most economical. Type 2 motor units are between 2.5 and 5 times less economical22 than Type 1. When they are mobilized, we observe an increase in the energy cost of muscle contraction.
A traditional strength training session allows for muscle recruitment based on Henneman’s principle. The heavier the load, the more a large quantity of motor units are solicited (initially Type 1 then progressively Type 2 depending on the magnitude of the load). An electrostimulation session allows for recruiting muscle fibers without respecting Henneman’s principle. It is therefore possible (but not guaranteed) to recruit a larger quantity of motor units and Type 2 fibers with lower loads. By relying on the lower efficiency of Type 2 fibers, one can thus increase the energy expenditure of a strength training session while using lower loads. Concretely, Kemmler et al.23 observed an energy expenditure of around 412 kcal for a strength training session combining electrostimulation and low-intensity strength training, and 352 kcal for the same session but without electrostimulation. It is also important to note a significant increase in the perception of effort between the 2 sessions (14.7 Borg RPE “difficult” for the session with electrostimulation vs 11.9 “light to moderate” for the session without electrostimulation).
However, the difference in energy expenditure will be smaller when the intensity of the strength training is higher (higher recruitment of motor units and Type 2 fibers). Electrostimulation therefore allows for increasing energy expenditure when submaximal loads are used.
Some authors also report an energy cost linked to recovery that is potentially higher than for traditional training24,25. The reported values seem relatively similar or higher than those observed for traditional strength training. It was not possible for me to find publications reporting the measured effects of electrostimulation on total energy expenditure. Although this method may increase post-exercise energy expenditure (recovery energy cost), this does not necessarily imply an increase in total energy expenditure. As with strength training, compensatory mechanisms can limit or cancel this energy increase26. Electrostimulation is unlikely to influence the energy balance differently than other forms of exercise, thus limiting its power of action on the energy balance.
Myths to demystify
Myth 1: “Electrostimulation melts fat” This is one of the most widespread myths. In reality, lipid oxidation depends on the global energy context, effort intensity, duration, nutritional status, and global metabolic adaptation. Local muscle stimulation does not automatically lead to significant localized fat loss.
The fact that a muscle contracts does not mean it specifically uses the subcutaneous fat located just above it. This idea of localized combustion is very seductive commercially, but it is not supported by robust scientific data.
However, a drop in the respiratory quotient post-electrostimulation training session is mentioned. This change in the ratio of produced CO2 and consumed O2 generally signifies a decrease in carbohydrate utilization for the benefit of an increase in lipid utilization. We could be tempted to conclude that electrostimulation training indeed promotes greater post-effort lipid oxidation, which could translate (possibly) into a decrease in fat mass.
Except that…
Based on respiratory quotient data from a few studies27,28, I have prepared three scenarios (Table 1) quantitatively presenting what could happen at the level of energy substrate utilization.
For each 100kcal expended at rest (because when intensity increases, carbohydrate oxidation also tends to increase), we can theoretically observe an increase of around 0.5g to 2.7g of fat burned. Assuming a person remains at rest throughout the day and nevertheless expends 2000kcal, electrostimulation would theoretically lead to an increase in lipids used of around 54g. Obviously, this scenario is unlikely, but it helps put the scale of the effect of electrostimulation on substrate oxidation into perspective.
Myth 2: “20 minutes of EMS is equivalent to several hours of training” This type of message abusively simplifies reality. One cannot directly compare an EMS session to several hours of training without specifying the type of effort, the goal, the intensity, the engaged muscle mass, and the intended adaptation. A locally imposed contraction is not equivalent to a full workout of strength, power, aerobic endurance, or mobility. Electrostimulation training primarily allows for increasing strength adaptations when relatively low loads are used. The more the intensity (the load or muscle tension in resistance training) increases, the more large-caliber motor units will be mobilized (the famous Henneman’s principle), thus limiting the potential contribution of electrostimulation to muscle recruitment (electrostimulation allows for locally stimulating motor units, but if they are already mobilized by the effort, the effect will not be additive).
Myth 3: “EMS replaces weight training” For a person capable of training, the answer is no. Electrostimulation can complement, facilitate, or offer possibilities for more specific muscle recruitment. But loaded weight training provides mechanical load, motor learning, coordination, progression, and a much more complete functional transfer. It proves more accurate to consider electrostimulation as another training modality, with its advantages and limits, rather than a complete training mode in itself.
Myth 4: “If it burns or shakes hard, it must be effective” Sensation is not a sufficient criterion. A strong electrical sensation ensures neither a good protocol, nor a useful effect, nor a functional transfer. Pain tolerance becomes a non-negligible limiting factor. The physical constraints of electrostimulation (the number of electrodes limited per muscle group, their fixed positioning) mean that motor units and muscle fibers will be primarily recruited “around” the electrode. This is not recruitment that is ordered or sequenced according to the movement and its characteristics, but rather based on the positioning and distribution of current through organic tissues. In order to extend recruitment, increasing current intensity can be painful and limit neuromuscular recruitment capacity (while potentially being unpleasant).
Precautions and Recommendations
Electrostimulation is not a harmless gadget. It must be used with discernment.
Some general precautions
- Read the manufacturer’s instructions and prioritize professional-grade equipment
- Start progressively
- Avoid seeking maximum intensity right from the start
- Monitor skin reactions under the electrodes
- Be cautious in case of unusual pain, cramps, or malaise
- In a clinical context, seek advice from a qualified professional
Contexts requiring particular caution Certain situations require a prior evaluation or a relative contraindication depending on the clinical context and the type of device:
- Implanted devices (needles)
- Certain heart conditions
- Pregnancy, depending on the area of application
- Skin lesions
- Specific neurological disorders
- Unexplained pain
- Unsupervised use of high intensities.
Conclusion
Electrostimulation is neither a total fraud nor a miracle solution.
It is a real tool, with effects documented in certain contexts, especially on muscle strength and as a complement in rehabilitation or for individuals who are not very capable of training. It can also, under certain conditions, contribute to modestly improving certain body composition parameters or complementing voluntary training.
But its effects are often oversold, particularly when it is attributed with a significant capacity to cause weight loss, massively oxidize lipids, or replace actual training. For aerobic capacity, aerobic endurance, power, or fat loss, the benefits are much more limited or much more context-dependent than marketing would have you believe.
The best way to view electrostimulation is therefore this: a complementary tool, sometimes relevant, but rarely central.
References
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