Neuromuscular electrical stimulation – Is it useful for training, recovery, and rehab?
Neuromuscular electrical stimulation (NMES) units, which send currents through certain areas of your body depending on where you attach the electrodes, are quite useful for injury rehab and also for training. This article explains the ins and outs of using NMES for rehab and training. It also takes a look at whether marketing messages that NMES units are good for post-exercise recovery are supported by science. Remember, if you need more help with an injury, you're welcome to consult one of our physios online via video call.
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What is neuromuscular electrical stimulation?
Your muscles contract in reaction to electrical pulses from your nerves. The number and type of muscle fibres that contract will vary, depending on what your brain thinks is required.
Your brain tries to minimise muscle contractions, because it’s always trying to find ways to preserve energy. This is a remnant from a time in the history of our species when energy preservation was a matter of survival – when you couldn’t drive to a McDonald’s or order pizza delivery when you were feeling a bit peckish.
In practice, this means that when you do a bicep curl, your brain will fire up just enough muscle fibres to get the job done and no more. If you want to work your muscles hard to make them stronger, you have to curl heavy weights to get as many fibres involved as possible.
An NMES unit enables you to “override” your brain and decide how many muscle fibres you want to stimulate to contract. So, you can cause strong contractions in the biceps muscle without having to use those heavy weights in our bicep curl example.
Depending on the frequency you select on the NMES unit, you can either recruit more of your slow-twitch muscle fibres, which are for endurance, at lower frequencies, or more of your fast-twitch fibres, which are more strength-based, at higher frequencies.
What type of NMES unit do I need?
The NMES unit (a Compex) we used at the sports injury clinic in which I used to work was state-of-the-art. But if you’re a recreational athlete and/or you’re looking for basic rehab functions, you can get away with an NMES home unit that’s much more basic and affordable.
The number of pre-set programmes on the machine can make a substantial difference to the price. You get programmes such as one for disuse atrophy, e.g. if you haven’t been able to use your legs for quite some time (like when it’s been stuck in a plaster cast), or for neurological rehab. But if you’re willing to read up on the frequencies that are useful for stimulating various muscle fibres, you can get an NMES unit that is somewhat simpler and then do the necessary settings by hand. The basic settings you’re looking for are endurance, strength, and recovery.
Another factor that influences the price of an NMES unit is whether the electrodes you stick on yourself are connected to the unit by cables or wirelessly. Obviously, with the wireless electrodes you are much freer to move about during your “workout”.
Here's a selection of NMES units on Amazon. Or you can go to the Compex Store.
Neuromuscular electrical stimulation for training
So, does NMES actually work for training? The research is quite clear that it can make your muscles bigger and stronger and increase endurance, depending on how you use it.
However, the research studies did not all use the same methodology, so it’s difficult to compare NMES units in this regard. For instance, you get better results if you don't just sit still and let the electrodes do all the work, but this is what some studies had their subjects do. So, if you want to exercise your leg muscles, you should also do gentle squats to activate the muscles and let the electrical current from the NMES unit augment the contraction.
Interestingly, not all of the gains are down to your muscle fibres growing stronger. There's also research to show that NMES activates your spinal as well as the cortical nerves in the brain, so that it gets those neural pathways to your muscles firing better. If your nerves fire better, your muscles can contract better and are more coordinated, and more fibres can be recruited more easily.
A few words of warning
When you do “actual” exercise, your muscle fibres get micro-damage, which your body then repairs into a stronger state than before while you rest between exercise bouts, which is how we naturally grow stronger. NMES units create the same type of micro-damage. So don’t add NMES to your routine and keep on training like before; you might end up over-training. Give your muscles enough recovery time between NMES and training sessions.
There have also been reports of people getting rhabdomyolysis, which is a potentially fatal condition where you get so much muscle damage from a single session that the resultant waste that your muscles excrete affects your heart and/or kidneys.
So, if you’re new to NMES, rather ease into it – as one should do with any new type of exercise – than dialling your NMES unit up to maximum from the start.
Neuromuscular electrical stimulation for recovery
One of the big selling points that the marketers of NMES units try to hammer home is that it works wonders for post-exercise or post-competition recovery. However, the evidence for this is not very strong.
We have to distinguish here between active and passive recovery. Active recovery involves some gentle activity, while passive recovery is just resting as much as possible. Using an NMES unit for recovery would obviously simulate active recovery.
A review of a group of research studies compared NMES recovery with passive and active recovery by looking at three issues: how quickly the recovery reduced blood lactate levels back to normal, post-recovery performance, and post-recovery pain and fatigue.
Getting rid of blood lactate: NMES was better than passive recovery, but no better than active recovery.
Performance: NMES wasn’t any better than passive or active recovery, and in one of the studies it fared worse. (You’re at risk of not recovering that well if you use an NMES unit on a setting that’s too high, or if you use it at all when you’re not very fit. In general, passive recovery works better for people who aren’t fit. So, make sure you choose your recovery according to your fitness level.)
Pain (DOMS) and fatigue: NMES produced better results than passive recovery but wasn’t any better than active recovery.
So, in a nutshell: if you’re doing active recovery anyway, you don’t need NMES on top of that. But NMES could be useful for recovery in a scenario where e.g. a football team has to get onto a bus for a long ride home right after a game, which would make active recovery impossible.
Neuromuscular electrical stimulation for injury rehab
I have found NMES really useful for people who have had a limb immobilised for a very long time or whose muscles are struggling to contract after certain types of surgery.
For example, when you remove the plaster cast or orthopaedic boot after an ankle fracture (usually after 6 to 12 weeks), it’s amazing how “dead” the calf muscles are. And after knee surgery, the quad muscles sometimes just don’t want to fire.
Because NMES activates the nerve endings, it can really get the muscle working much quicker than if you tried to get them working properly again just with regular exercise.
Another good rehab use of NMES is to exercise muscles when a joint injury, such as a meniscus tear, makes regular exercises impossible or very painful – especially in the initial stages of rehab.
Like with regular rehab exercises, you have to start gently so that you don’t re-injure yourself. You can do this by going for the “disuse atrophy” setting on your NMES unit or, if this setting isn’t available, setting up your session so that the rest periods between contractions are quite long. If the machine doesn’t allow you to do that either, just use the endurance setting and go for shorter sessions to start with; the typical standard session duration on an NMES unit is 30 minutes, so maybe switch it off after just 10 minutes.
As with normal rehab exercises, if a session hasn’t caused you pain during or in the 24 hours afterwards, you know you’ve used your NMES unit right.
How we can help
Need more help with your injury? You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.
We're all UK Chartered Physiotherapists with Master’s Degrees related to Sports & Exercise Medicine. But at Sports Injury Physio we don't just value qualifications; all of us also have a wealth of experience working with athletes across a broad variety of sports, ranging from recreationally active people to professional athletes. You can meet the team here.
About the Author
Maryke Louw is a chartered physiotherapist with more than 20 years' experience and a Master’s Degree in Sports Injury Management. Follow her on LinkedIn and ResearchGate.
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