What is Electrical Stimulation?
Electrical stimulation (ES) is a technique by which an athletic trainer or rehabilitation professional applies electric current to the muscles. This can be done via electrodes attached to the skin or by electrodes implanted under the skin.
ES is used to increase muscle strength, improve muscle endurance, and speed up the recovery process from injury.
Types of electrical stimulation
There are two primary types of electrical stimulation:
- Neuromuscular electrical stimulation (NMES)
- Transcutaneous electrical nerve stimulation (TENS)
Both methods are used to increase muscle strength and endurance. NMES is used to activate muscles independent of voluntary commands from the brain.
This is particularly useful for athletes with muscle damage or any person with a neurological condition that affects the ability of the motor pathways of the brain to activate specific muscles. NMES can be used alone or in conjunction with voluntary muscle contraction.
Electrical stimulation for athletes
NMES can be used to target specific muscle groups involved in sport-specific skills. For example, NMES can strengthen the quadriceps muscles in basketball players where jumping is required or the pectoralis major muscle in freestyle swimmers.
Through the targeted use of NEMS to isolate specific muscles or muscle groups, athletes can improve muscle performance and reduce the risk of injury.
Whereas NMES is more viable for muscle strength and endurance gains, TENS is more likely to be used to alleviate pain and reduce inflammation in injured muscles and joints.
TENS works by manipulating the nerves that transmit pain signals to the brain, which can help to alleviate the perception of pain. In that way, TENS acts as an analgesia, either perceived or actual nerve-blocking.
It may also help to facilitate the flow of oxygen-rich blood to injured tissues, which can accelerate the healing process.
NMES after knee surgery
Loss of quadriceps strength after knee surgery is a major issue for athletes. To examine the effects of early NMES post-surgery, researchers in 2020 examined athletes with an acute, first-time ACL rupture.
Subjects either received NMES five days per week or simulated microcurrent electrical nerve stimulation treatment to the quadriceps muscles of their injured leg.
Researchers performed bilateral biopsies of the vastus lateralis three weeks after surgery to measure skeletal muscle fiber size and contractility. They assessed quadriceps muscle size and strength six months after surgery.
Results showed that NMES reduced muscle fiber atrophy, increased maximal contractile velocity, and preserved muscle power output. However, there were no differences in whole muscle strength between the two groups.
These results demonstrate the effectiveness of the early use of NMES to mitigate some of the skeletal muscle maladaptation to ACL reconstruction.
NMES with blood flow restriction
Athletic trainers and rehabilitation professionals have also shown recent interest in combining NMES and traditional resistance training with blood flow restriction (BFR). The intent is to increase muscle cross-sectional area (CSA) or total muscle mass or size.
CSA is important to athletes because the total size of a muscle contributes directly to muscle strength and power capabilities. Both are paramount to athletic success.
In practice, BFR requires the use of a tourniquet or cuff to partially restrict blood flow to the muscles during training. Researchers believe this increases metabolic stress and overall muscle activation.
A recent study (Bergamasco, et al., 2022) compared the effects of low load-blood flow restriction (LL-BFR; traditional resistance training) and neuromuscular electrical stimulation-blood flow restriction (NES-BFR; electrical stimulation) on vastus lateralis cross-sectional area, rate of perceived exertion (RPE), and pain in 15 healthy young males.
The results showed that vastus lateralis CSA significantly increased in both groups. However, the LL-BFR group demonstrated significantly greater CSA changes than the NES-BFR group.
This means that actual resistance training with blood flow restriction produced greater muscle hypertrophy than NES with blood flow restriction. LL-BFR also produced significantly lower RPE and pain responses than NES.
These results demonstrate that, although NMES is a tool to develop muscle mass, strength, and power, it is not a replacement for traditional resistance training.
A useful tool
ES is a valuable tool for both athletic trainers and athletes alike. It can help athletes who want to improve athletic performance, prevent injuries, and facilitate recovery.
It is not, however, a substitute for traditional resistance training and should be used primarily for injury recovery and only by trainers with knowledge of ES methods and best practices.
This article was written by Amy Ashmore, PhD.