By Steve Bechtel

I am as excited about the next big thing in training as the next guy. When Electronic Muscle Stimulation (E-Stim) came on the scene, I could almost feel my forearms getting stronger just thinking about it. It was a great idea for climbers; a way to train the forearm muscles when you can’t climb, or when the joints or skin are too trashed to train. The idea of being able to build more endurance by stimulating the muscle fibers at the end of a long climbing day made total sense.

In a nutshell, you slap a couple of sticky electrodes to your skin (climbers would do this on the muscle belly of the forearm flexors) and hook them up to a low-voltage unit that cyclically jolts them with electricity. Clinical trials done in physical therapy settings show good maintenance of muscle bulk and some increase in strength, especially in otherwise immobile muscles. Research on active individuals is not so solid. In highly trained individuals (and let’s face it, any climber considering E-Stim is probably way up there in the forearm strength/endurance percentile) there is very little evidence that it helps improve either strength or endurance.

But it gets worse. Seeing no improvement is bad, but research now shows that these things can actually make you weaker, and here’s how. Muscles generate force not through the strength of individual fibers, but primarily through a concerted effort of many, many fibers firing together all at once. In fact, there’s an entire branch of training methodology dedicated to “recruitment training”, with protocols designed to teach the muscles to use are greater percentage of fibers together in each movement. Greater recruitment is how a skinny guy can be stronger than a muscular guy. It’s also how grandma lifts the forklift off a screaming baby.

This is achieved through an unbelievably complicated system of electrical nerve impulses responsible for communication and coordination, and is not helped by jolts of electricity through the skin. The research suggests that the E-Stim, although helpful in stimulating individual muscle fibers, is basically jacking the whole communication system, sending a confused signal to the muscles. Think of hitting all the keys on your keyboard at once in an attempt to type faster (hjuyn.lonUb BVPEG-QE4[OHNV[‘LO). Confusing isn’t it?

I think these units are probably a good idea if you are injured, or as part of a practical joke. Slap them on and you do feel the pump…but it’s probably just a simulation of overload. It’s pretty clear that you are doing yourself no favors by trying to use them as part of a high performance training program.


  1. Szu-Ping Lee on June 18, 2019 at 5:03 pm

    The chronic e-stim model can indeed weaken the muscles, but it is not because it “jacking the whole communication system, sending a confused signal to the muscles.” as stated in your article. The muscle fibers respond to tension, and e-stim that does not achieve high enough muscle tension (which is 99% of all protocols) won’t have a strengthening effect. In fact, the chronic stimulation model proves that prolonged low level e-stim caused the muscle to become very efficient at producing constant, low level contractions via changes such as higher proportion of Type I fibers, increase mitochondria density…etc. But the muscle overall is weaker after such treatment.

    I am a biomechanics researcher and teach exercise physiology and electrophysiology. If I may suggest a reference book to learn more about this: Skeletal Muscle Structure, Function, and Plasticity (Lieber 2009).

    • Petar Chalamov on February 8, 2021 at 10:03 pm

      Super interesting! Thanks for the info (as well as the comment above!!). I just got my hands on a Estim as part of a knee surgery recovery protocol and immediately thought about climbing:)

      Would you consider that there will be some capillary benefits to the forearms from using E stim? The major physiological benefit from ARC training (at least in my amateur understanding) is that blood goes to the muscles for longer time applying pressure to the capillries and eventually making them wider – helpful when ure shaking off on a jug.

      So while Estim could (temporarily?) offset some of your max strength requirement gains it might support you by boosting recovery times. Isnt that the same as ARC training anyways?!

  2. Rhianna on October 8, 2022 at 8:54 am

    What do we think about estim for antagonist muscle training

  3. Steve Bechtel on October 8, 2022 at 1:06 pm

    Probably OK if necessary in a PT or assistance environment, but not as a replacement for normal strength training. The book Szu-Ping recommends is excellent and is quite enlightening.

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