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Electrical muscle stimulation (EMS), neuromuscular electrical stimulation (NMES), and electromyostimulation, all refer to the elicitation of muscle contractions using electric impulses. EMS began gaining popularity in the early 1970’s largely due to Dr. Kots claim that EMS stimulation in elite athletes resulted in force gains of up to forty percent1. Since this claim was made there have been numerous studies performed on all of the different applications of EMS training and its effects on muscle mass, muscle strength, muscle recovery, and preventing muscle atrophy. Before we cover the different applications of EMS, it is important to understand how EMS interacts with the body. During voluntary muscle contractions, the human body follows a pattern known as Henneman’s Law2. According to this principal, the smallest motor units (also known as slow twitch muscle fibers) are activated first due to their low recruitment thresholds. As the demand on the muscle increases, the bigger motor units (Fast-twitch) begin to be recruited. EMS reverses this pattern through three methods:
- EMS has shown preferred recruitment of superficial motor units over deeper ones4
- Snyder-Macier et al. have established that fast twitch motor units have a tendency to be closer to the skin surface3
- Cutaneous receptors tend to increase the recruitment of fast twitch fibers over slow twitch ones5
To summarize, EMS stimulation first tries to recruit the muscle fibers closest to the skin, which are fast-twitch muscle fibers, and because EMS stimulation is transcutaneous, the skin receptors also begin recruiting fast-twitch fibers over slow ones.
Now that we have a basic understanding of the science behind EMS therapy we can take a deeper dive and understand how these different methods result in increased muscle mass, strength, recovery, and the prevention of muscle atrophy.
- Muscle Mass: EMS is able to aid in muscle hypertrophy due to the micro-trauma that is caused by EMS caused muscle contractions, in fact evidence suggests EMS training leads to more micro-trauma than concentric training6, and because we know EMS targets fast-twitch muscle fibers we can assume that the hypertrophy from EMS training occurs mostly in these fibers.
- Muscle Strength: EMS is capable of increasing strength; these gains are mediated through both increases in muscle hypertrophy and neuromuscular adaptations. A common misconception of EMS training is that since EMS replaces the central nervous system in activating the muscles, there are no neuromuscular adaptations; there is a lot of evidence suggesting the opposite. One study in particular suggests that EMS training can increase the recruitment of motor-units by lowering the activation/innervation thresholds of the muscle fibers8. EMS can increase strength and is capable of accomplishing this in a short time frame, some studies claim substantial increases in strength as early as three weeks into training programs7.
- Muscle Recovery and Atrophy Prevention: Sub tetanic EMS therapies can be used to increase recovery by using pulsating contractions, acting like a sport massage and stimulating blood flow to the muscles by creating a pumping effect. EMS can help the prevention of muscle atrophy from inactivity because EMS has shown increases in muscle size and strength, and can be used on a muscle or group of muscles when regular training is not possible
- Alex R. Ward, Nataliya Shkuratova; Russian Electrical Stimulation: The Early Experiments
- Elwood Henneman; The Size-Principle: A Deterministic Output Emerges From A Set of Probalistic Connections
- Manuel Mercier et al: Neuro-Oscillatory Phase Alignment Drives Speeded Multisensory Response Times: An Electro-Corticographic Investigation
- Vladimir Medved: Measurement of Human Locomotion
- Struppler and Weindl: Clinical Aspects of Sensory Motor Integration
- Kazunoru Nosaka: Muscle Damage Induced by Electrical Stimulation
- Babault, Cometti, Bernardin; Effects of Electromyostimulation on Muscle Strength and Power of Elite Rugby Players
- Niccola Maffiiuletti: Neural Adaptations to Electrical Stimulation Strength Training