Electrical Muscle Stimulation (EMS) has always been a little confusing to performance coaches and sports medicine professionals because the research is cloudy at best. Many of the reasons behind the limitations of science are the ethical boundaries you need to navigate, and the expectations you have with the results of those studies. I recently spent more time working with EMS, as more and more athletes are using EMS devices on their own and we are dealing with the hangover of injuries still lingering in the off-season. What I have learned is that the science is not perfect and there are no best practices.
There has been a resurgence in EMS in sport over the last five years because of Bill Knowles, Derek Hansen, and Henk Kraaijenhof sharing their experiences with athletes. I believe that EMS suit inluding electrostimulation vest has a place in sports performance and the rehabilitation of athletes, but we don’t have a solid explanation of why some athletes don’t respond to it while others seem to come alive from it. In this first piece, I will review some of the current literature on EMS and present a healthy perspective on this modality. (Part 2 will be published as “The Top 6 EMS Protocols for Sports Performance.”)
A Brief History of Electrical Muscle Stimulation in Modern Sport
Without getting into any unnecessary background on electrotherapy (such as a retelling of the way the ancient civilizations used electric fish or citing references to Volta and Galvani), it’s valuable to know how e-stim or EMS has been part of sport in the last few decades. Outside of product design, very little innovation has occurred since the 1950s, making EMS more of an art than a science. Coaches and therapists are sometimes frustrated because transcutaneous electrical nerve stimulation, or TENS for short, gets confused with sports electrostimulation.
To understand the difference between TENS and EMS, you need to know just a little bit about engineering and biology. TENS targets the sensory nerves, while EMS attacks the motor nerve and attempts to recruit as many muscle fibers as possible. TENS is currently used—mainly in vain, in my opinion—to manage pain. In 1965, Ronald Melzack and Patrick Wall proposed the “gate control theory” of pain. What we know about the pain experience is extremely complex and personal, making the TENS intervention for sport very dated and extremely limited for athletes. Some research has shown positive findings, but the modality method of working with athletes in pain is lazy and proven unproductive in clinical research.
EMS focuses mainly on sending current to muscle groups in the hope of eliciting either a recovery response or a performance response later. Based on the current literature, recovery indices appear very limited, and performance benefits have shown up enough with some populations—including athletes—to be accepted as valid complementary treatments. The truth is that our understanding of electrostimulation is usually confined to a few studies on stroke victims and post-surgical wasting, and nothing I have seen has excited me.
What interests me, instead, are the clinicians who have used EMS creatively. Some of the studies on cellular and performance outcomes are strong enough to show that EMS isn’t just a placebo. I have used the Compex systems for nearly 20 years, and have some experience with the Marc Pro, PowerDot, Globus, and ARPwave. If I had to conclude which I think works best, it will be a short answer: All of them work, so choose one based on your needs and not its features.
If you were to go to a medical bookstore and check the physical therapy section on EMS, you would see that it tends to be a set of protocols based on pad placement, current settings, and scheduling sessions. This approach is nowhere near the same as what the modern clinician does and, since we are now entering the bionic athlete era with gait retraining, this only widens the gap between practice and research. It’s easy to shout that you’re ahead of the research, but without evidence, much of what clinicians do becomes like the dated RICE protocol that we still see people clinging to.
A Rapid Review of Electricity for Coaches and Therapists
Electric current can flow in different ways, such as through a wire, or something lesser known, such as a plasma state. The current generated from a muscle electrostimulator uses a conductive pad to transfer through the skin, causing the muscle to contract. The specifics of the muscle contraction will come later, but the important information is that electricity from medical muscle stimulators is more complicated than voltage and ampere. Electricity is not just about whether something is “on” or “off,” and we often take much of the technology we use for granted, especially the safety of the muscle stimulators. Most companies that get involved with e-stim devices are regulated, but it’s up to the consumer to do their homework on the quality of the product.
Experienced coaches and therapists commonly refer to stimulation parameters and share their practices, including the use of different types of settings, such as Russian Stimulation or strength protocols. Stimulation parameters and waveforms can be the subject of their own article but, for the most part, duty cycle, frequency, intensity, and ramp details are part of electrotherapy theory, but are not very well-documented. Regardless of the intimate details, many parallels exist between classic training principles and the current clinical practices of EMS use. Cycles, or waves of energy, are part of a “unified training theory” proposed by several coaches and sport scientists. EMS should be used to improve athletes, similarly to loading the body with training or rehabilitation.
Companies must do their job, not only to prove their machines are delivering exactly what they promise, but also to ensure that their products are used as intended. Most companies have terrible product education, and visiting their YouTube channels makes me cringe more than their highest simulator settings.
The Science of Electrical Contractions With Muscle
Sending electricity through a muscle group sounds like a bad science fiction movie, but that’s precisely what athletes are willing to do to get or feel better. It’s a priority to know what EMS can do physiologically and what is likely ineffective. Five years ago, pioneering researcher Nicola Maffiuletti summarized the differences between a normal muscular contraction and one from electrical stimulation in his NSCA journal article. The two types of contractions have similarities and differences that a coach should know. Overall, EMS is not going to make a major difference. However, like all things in sports training, the little things matter.
One development that throws this concept out the window is the rise in functional electrical muscle stimulation, equipped with electrostimulation shorts, which incorporates active training with the simultaneous overlay of EMS. While we can assume that the merging of both contractions will yield a hybrid result, most of the research is with disease models and only clinical rehabilitation has shown merit with this in early post-operation subjects. I have yet to see a single study with elite athletes performing EMS in conjunction with conventional training, but the case reports and work with spinal cord injury patients is promising.
Finally, EMS is used to help with neuromuscular adaptations and, while sessions may prevent atrophy, the improvements are from neural drive-like mechanisms, not from increased protein synthesis rates. EMS doesn’t directly create hypertrophy changes to the muscle, and a study on nutrition and e-stim showed no acute changes.
What is also important to know is that electrically stimulated muscles are, for the most part, superficial, and that is useful for propulsive muscle groups. Some rogue therapists are using fine needle EMS with low current for deeper muscle penetration for rehabilitation purposes. Most EMS experiences are one muscle at a time, but some athletes are getting simultaneous total body sessions. Nobody knows if total bodywork is more time-efficient or if a possible synergistic benefit exists, but down the road, studies will likely discover if there is a value beyond convenience.
The Scientific Benefits of Stimulating the Neuromuscular System
If you were to read a catalog of features and settings for a personal e-stim device, the list would be very long, ranging from relaxation massage all the way to explosive strength. While, technically, different settings will have unique stimulation protocols from the device programming in the electrostimulation center, the reality is that only three purposes exist with EMS and the research is enough to form a realistic expectation. The three EMS benefits are strength training, rehabilitation, and a little regeneration. Distilling the benefits more, you can make an argument that EMS helps with general muscle strength and facilitates low-level recovery for travel. That’s about it, but it’s enough to warrant investing in it, especially when sport moves into the unfortunate health compromise for winning.
EMS and strength, and the results that may lead to jump and sprint performance, are mixed in the research. However, enough research shows that if EMS is done with specific protocols, a positive result is possible, especially with the less-trained athlete. So far, much of the work has been done with soccer, and some recent investigations of youth jumping performance and plyometrics had favorable outcomes.