What are electrical muscle stimulators (EMS)?
Electrostimulation has become one of the most powerful tools in recent years. Over time, the sector electrical muscle stimulators have become increasingly professionalized and we have gone from the application of local electrodes with very small patches to systems fully packaged in electrostimulation suits. Electrical muscle stimulators emerges as a new training methodology that reduces training time offering the same or even better results than conventional training.
We already know that the prevalence of obesity and sedentary lifestyle has skyrocketed in recent years in all parts of the world. Low physical activity and the increase in hypercaloric diets based on ultra-processed foods has caused our society to transform into a sick society. In this sense, physical activity seems to be a useful tool to reduce the numbers of obesity, both in adulthood and in childhood and adolescence. According to world organizations such as the World Health Organization, we should all perform at least 150 to 300 minutes of moderate aerobic physical activity and between 75 and 150 minutes of vigorous aerobic physical activity. These recommendations are transmitted from the competent authorities with the aim of alleviating the effects of sedentary lifestyle and poor nutrition.
However, although these recommendations and interventions seem to be useful, they do not generate sufficient adherence to introduce them into the lifestyle of the population. In addition, one of the main barriers that people usually show to not perform physical exercise is the lack of time. We live in a society in which everything happens very quickly and sometimes we do not have the physical time to spend 1 hour or 2 hours exercising, getting into a body-combat class or going out to do a bicycle route.
In this sense, electrical muscle stimulators have managed to design a new methodology that in approximately 20-30 minutes can achieve the same effect as a conventional session. However, activating the muscles passively and uncontrollably can have a detriment to health. In fact, there is some study that indicates that malpractice during a workout with electrical muscle stimulators can lead to serious health problems.
However, this does not have to scare us since the effects of well-controlled electrical muscle stimulators are the same effects we have when we exercise. One of the main fears of electrical muscle stimulators is that it can lead to too much muscle damage and raise a protein called CK (creatine kinase) that can cause kidney problems. This protein rises in the blood when performing a very high intensity exercise in untrained people. In fact, this can happen to anyone who goes to the gym for the first time and their trainer designs a workout that is too demanding for that person.
How do electrical muscle stimulators work?
Once the fear that electrical muscle stimulators can be dangerous has been overcome, we have to take into account that there are multiple electrical parameters that can be modified and whose relationship will provoke one response in the body or another. So that we can have a very basic idea about these electrical parameters we will explain the 4 basics: frequency, intensity, pulse width and work/rest time:
- Frequency: Indicates the number of pulses per second and is measured in Hertz (Hz)
- Intensity: Indicates the amount of electrical current passing from the artificial device to the person and is measured in milliamps (mA).
- Pulse width: Indicates the total time each electrical impulse is innervating the muscle and is measured in nanoseconds (μseg)
- Work/rest time: It is the time in which the electrostimulation is activated and the time it is stopped.
This last parameter requires greater attention since electrical muscle stimulators (hereinafter EMS) will never be active at all times, but work and rest times will be interspersed. Here is an illustrative image of what we have just explained:
In the image we can see that this time the electrical muscle stimulators are acting with a frequency of 4 Hz (4 pulses per second), at 85 mA (amount of electric current that is transmitted) with a pulse width that several between 200 and 400 μseg and a time of 30 seconds electrical muscle stimulator active and 30 seconds electrical muscle stimulators off.
Knowing these electrical parameters is of vital importance to be able to understand the effects that studies and exercises with electrical muscle stimulators have and have had. Thus, for example, it would not be the same to put 1 Hz at 100 mA with a work/rest time of 10/50 than to put 100 Hz at 100 mA with a work/rest time of 4/4. After all, it is the same as training with loads, it would not be the same to do 10 sets to 1 repetition with 100 kg and rest 10 seconds between repetitions than to do 5 sets of 10 repetitions with 10 kg and resting 1 minute between sets.
As in the training variables we have to control very well how we combine them so that they give us a specific result in training with electrical muscle stimulators we must also do it.
Electrical muscle stimulators have changed a lot over time. Early devices used local electrodes while now there are complex electrical muscle stimulators suits that innervate the entire body at once. In this sense, it has been shown that local electrical muscle stimulators have effects for the improvement of strength and power.
What does science say about electrical muscle stimulators?
A systematic review with meta-analysis carried out by Filipovic and collaborators in 2012 collected the scientific evidence created so far to give a series of tips to follow when using electrical muscle stimulators (1). In this systematic review the aim was to see what electrical parameters and under what circumstances electrical muscle stimulators seemed to improve fitness parameters in trained and elite athletes. The result of their study seems to indicate that electrical muscle stimulators is a good tool to enhance the gains of maximum isometric force, dynamic force or the RFD curve.
Let’s go on to analyze one of the studies carried out in the early 2000s where they wanted to check if electrical muscle stimulators could help improve vertical jumping in volleyball players. The intervention time was short (4 weeks) but, apparently, they obtained significant changes both at 2 weeks and at the end of the intervention. In this case, the type of intervention was quantified with the number of contractions caused by electrical muscle stimulators and followed the following scheme:
- Frequency: 115-120 Hz
- Intensity: 60-120 Ma
- Pulse width: 400 μseg
- Work/rest time: 3/17
- Session duration: 26 minutes
The results show that the electrical muscle stimulators intervention was effective since by week 2 of the intervention the strength of the leg extension had increased by 20% and the strength of the plantar flexors by 13%. And not only that, at week 4 they got better in the “squat jump” (21%) and in the “spike countermovement jump”. Therefore, from this study we can conclude that electrical muscle stimulators has been effective for the improvement of vertical jumping in volleyball athletes. It should be noted that the training was not carried out only with electrical muscle stimulators but was also accompanied by a plyometric exercise-based training (2).
On the other hand, we will analyze a study carried out in a single athlete in this case weightlifter to see if electrical muscle stimulators was useful in their preparation (3).. In this study, in addition to checking if there have been improvements in sports performance parameters, muscle biopsies were also taken to see if the number of fibers was the same or if the type of muscle fiber had been modified thanks to electrical muscle stimulators.
On this occasion, electrical muscle stimulators training followed the following pattern:
- Frequency: 75 Hz
- Intensity: 200 Ma
- Pulse width: Unknown
- Work/rest time: 11/180
- Session duration: ≈ 30 minutes
This study is very nice because it tells us the change that has been in the type of muscle fibers of the quadriceps. However, we are going to stay with the part that interests us the most: performance.
In the previous image we have two different moments: A and B that mark when EMS is not used (A) vs when it is used (B). In all cases we see that using electrical muscle stimulators seems to improve the weight values lifted by this professional lifter in all modalities (squat, clean and jerk and snatch). Therefore, we can conclude that in this case electrical muscle stimulators also seems to offer guarantees of improvement.
Finally, I would like to end this blog by remembering that well-applied EMS is not harmful to the athlete and that it can increase their motivation, their adherence and of course their fun. Electrical muscle stimulators are a useful tool and not only at the physical level but also at the contextual level.
Unai Adrián Pérez de Arrilucea Le Floc’h
1.Filipovic A, Kleinöder H, Dörmann U, Mester J. Electromyostimulation—a systematic review of the effects of different electromyostimulation methods on selected strength parameters in trained and elite athletes. The Journal of Strength & Conditioning Research. 2012;26(9):2600-14.
2.Maffiuletti NA, Dugnani S, Folz M, Di Pierno E, Mauro F. Effect of combined electrostimulation and plyometric training on vertical jump height. Medicine and science in sports and exercise. 2002;34(10):1638-44.
3.Delitto A, Brown M, Strube M, Rose S, Lehman R. Electrical stimulation of quadriceps femoris in an elite weight lifter: a single subject experiment. International journal of sports medicine. 1989;10(03):187-91.
Graduado en Ciencias de la Actividad Física y del Deporte.
Investigador en el grupo PROFITH-ACTIBATE.
Máster en investigación de la Actividad Física y el Deporte (UGR).
Doctorando en el programa de Biomedicina por la Universidad de Granada (UGR).
Colaborador del "The Voice of Science".