Electric Muscle Stimulation (EMS) Training
We live in a society that embraces convenience, what could easily be referred to as a McDonalds mindset. We want it standard, quick and certainly easy. This mindset has translated to fitness. How often do you see an advertisement that you can get 6-pack abs in just 10 minutes a day; if you wear this belt to the gym, fat will melt away; buy this new machine and you will look just like this guy here..
Trying to optimize time spent training is not necessarily a bad thing. Not everyone has 2-3 hours to spend in a gym (nor wants to spend that time). A relatively new fitness trend is Electric Muscle Stimulation (EMS), also known as Neuromuscular Electric Stimulation (NMES). For the purpose of keeping it simple, we will refer to this as EMS.
EMS is not a new application to athletics. It has applications as a tool for strength training, rehabilitation, testing and for recovery. However, what we see now in centers marketing EMS is a break from the traditional use. As an example, a local center here in Santiago claims to work 350 muscles/session, that 20´ is equivalent to 3 hours in the gym and that all desired results can be achieved with 2 sessions/week. Those are some pretty bold statements. So, let´s look at EMS more closely.
What is EMS exactly? EMS stimulates the muscles repeatedly, at random. The nature in which the muscles are stimulated (superficial, spatially fixed and incomplete) implies that the same motor units are repeatedly activated by the same amount of electrical current and therefore brings on muscle fatigue more quickly. As a result, this can cause profound muscle damage.
Muscle damage is any injury or harm that impairs muscle function. This damage can range from a small micro injury of the muscle fibers to a complete disruption of muscle function. At any point where there is a loss of function to the muscle for a period greater than 2 days, this is an indicator of muscle damage.
Muscle damage can also be tracked by looking at the levels of Creatine Kinase (CK) and Myoglobin (Mb) in the blood. CK is found in the heart, brain, skeletal muscle and other tissues within our body. When muscle damage occurs, CK is released into the blood and overall levels increase. These increased levels are associated with rhabdomyolysis (to which we will refer to as rhabdo). Mb is found in muscle tissue and its function is to provide extra oxygen to release energy to power muscle contractions. When muscles are damaged, concentrations of Mb enter the kidneys where it is toxic and contributes to acute renal failure.
Let´s look at two different studies, one focusing on the longer leg muscles (there is some research to support that the longer muscles are more susceptible to damage with EMS) and one examining the effect on the biceps brachii and brachioradialus.
The first study involved ES-evoked isometric contractions of the knee extensors. Stimulation was increased towards maximally tolerable levels. Two sessions were completed two weeks apart using the same muscles. The study resulted in a maximal voluntary isometric contraction (MVC) strength below baseline by 30% after ES for 2 sessions. Additionally, levels of CK were significantly higher after 4 days for the first session. (3)
In the second study, participants were tested doing preacher curls. The control group performed the movement without ES while the ES group was stimulated at the biceps brachii and brachioradialus. The average peak torque was significantly greater for voluntary contractions. While MVC decreased for both groups, the decrease was significantly greater and recovery significantly slower for ES vs. MVC. The magnitude of soreness was significantly greater 2-3 days post exercise for ES. Finally, there was a significant increase in CK 4 days post exercise for the ES group.
EMS can be a useful tool to supplement resistance training (weights), but should not be used to replace it.
Pre-training measurements and assessments of thyroid and kidney functions should be conducted to identify risk of rhabdo.
EMS requires a greater recovery time than traditional training to allow the CK blood levels to return to an acceptable level (especially in the beginning). By performing this training without proper recovery time, the client increases the risk of rhabdo.
Despite claims, studies have shown that resistance training has a 50% greater effect at reducing body weight over EMS. Additionally, EMS has no significant change in the waist to hip ratio, while resistance training does.