Since I plan to discuss a number of studies on electric stimulation, I figured I should get this one out there. It gives some background as to which electric stimulation parameters work for increasing muscular performance so that people can judge if what they are doing (or plan to do) is anywhere close to the ballpark of what works. There are countless electric stim machines out there that range from less than $100 to many thousands of dollars, and this is a case where it’s not as simple as “you get what you pay for”. Rather, you have to know what works and if a given machine can do that or not. In that sense this review is incredibly useful. The abstract, which is a bit daunting, is as follows:
“Our first review from our 2-part series investigated the effects of percutaneous electromyostimulation (EMS) on maximal strength, speed strength, jumping and sprinting ability, and power, revealing the effectiveness of different EMS methods for the enhancement of strength parameters. On the basis of these results, this second study systematically reviews training regimens and stimulation parameters to determine their influence on the effectiveness of strength training with EMS. Out of about 200 studies, 89 trials were selected according to predefined criteria: subject age (7 days). To evaluate these trials, we first defined appropriate categories according to the type of EMS (local or whole-body) and type of muscle contraction (isometric, dynamic, isokinetic). Unlike former reviews, this study differentiates between 3 categories of subjects based on their level of fitness (untrained subjects, trained subjects, and elite athletes) and on the types of EMS methods used (local, whole-body, combination). Special focus was on trained and elite athletes. Untrained subjects were investigated for comparison purposes. The primary purpose of this study was to point out the preconditions for producing a stimulus above the training threshold with EMS that activates strength adaptations to give guidelines for implementing EMS effectively in strength training especially in high-performance sports. As a result, the analysis reveals a significant relationship (p < 0.05) between a stimulation intensity of ≥50% maximum voluntary contraction (MVC; 63.2 ± 19.8%) and significant strength gains. To generate this level of MVC, it was possible to identify guidelines for effectively combining training regimens (4.4 ± 1.5 weeks, 3.2 ± 0.9 sessions per week, 17.7 ± 10.9 minutes per session, 6.0 ± 2.4 seconds per contraction with 20.3 ± 9.0% duty cycle) with relevant stimulation parameters (impulse width 306.9 ± 105.1 microseconds, impulse frequency 76.4 ± 20.9 Hz, impulse intensity 63.7 ± 15.9 mA) to optimize training for systematically developing strength abilities (maximal strength, speed strength, jumping and sprinting ability, power).”
My comments:
In the text they look at all aspects of electric stimulation: the type of wave, the intensity, duration, rate, etc. The authors discuss how it performed with an emphasis on athletics, give a summary of the results with regards to what seemed most effective, and give some ballpark figures to work with. Though the paper attempts to focus more on the training of healthy athletes, I find that information invaluable in rehabilitation situations as well. Unless I have reason not to, I tend to use similar (but not always the same) parameters with my patient population. Reading each section, what the authors note/recommend is as follows:
- Impulse type/form: biphasic square wave is emerging as the current favorite
- Training Frequency: 3 days per week
- Contraction time: 3-10 seconds
- Duty Cycle: 20-25%
- Impulse Frequency: >60 Hz
- Impulse Width: 200-400 uS
- Impulse intensity: >50 mA
The guidelines are all a little rough, but this paper describes parameters that current research is pointing towards. It’s more current and usable than any electric stimulation book I have read. Unfortunately, while it is pretty well established that electric muscle stimulation works, there are still a lot of unknowns with regards to what works best.
Training 3 times per week sounds like a good place to start, however I think if a person’s muscles are particularly atrophied and difficult to activate, more frequent stimulation might be better. Some studies on post-op knee replacement have stimmed 2 times per day with beneficial effects. On the other hand if muscle is developed and the stimulation intensity is high, I think 3 times per week might be too much for adequate recovery between workouts. In my own training where I have worked up to a high intensity of stimulation, training each bodypart every 3rd day feels about right.
In terms of contraction time, 3-10 seconds sounds right. I usually use 10 seconds on and 50 off, but I do so largely by appealing to the authority of Kots (Russian stim) and Charlie Francis’ work with his sprinters. Duty cycle of 20-25% sounds good, but the famed “Russian stim” parameters is a 10 second on 50 second off, which equates to about 16% duty cycle. I liken this to lifting weights when people ask what number of reps is best. The answer is “it depends.” The idea of the long rest period of 10 on 50 off is that your muscles are able to recover more fully and thus contract harder during each upcoming contraction. I do notice however that if I shorten the rest period, upcoming contractions are not as hard, but I am then able to turn up the intensity of the machine and reach new muscle fibers. This makes me wonder which contraction time pattern is more effective in the long term.
Impulse frequency >60 Hz sounds right according to most research I have seen and is enough to give a tetanic contraction. I use 120 Hz because I first became interested in electric stimulation after reading sprint coach Charlie Francis’ book, and that’s what he used. I have yet to find any reason to change it. 120 Hz feels more smooth than 60 Hz for what that is worth.
In my experience impulse width is underappreciated and is as important as intensity. 200 uS seems a bit short to me. It will probably work fine for arms but won’t be enough for core or leg musculature. 300 uS is pretty stout, will adequately train most anyone, and can be found in inexpensive but quality stim machines (i.e. the EV-906). 300 uS is also strong enough that most people will not be able to max out. I do notice my patients with neuropathy in the calves and feet, 300 uS at 100 mA often isn’t enough to get a strong muscle contraction. However, in that case the Globus unit with the availability of 450 uS is enough to get good muscle activation out of all but those with full denervation.
Impulse intensity over 50 mA sounds reasonable. If the pulse width of the machine is just 50 uS, then 50 mA isn’t going to feel very strong, but bring the pulse width up to 300+ and it’s another matter altogether. For optimal strength the research seems to suggest that more intensity is better. Work up to as much as you can take!
Not addressed in this paper but worth knowing: I find you can comfortably get more current into a large muscle by adding electrodes rather than just turning up the electrodes. Two electrodes (1 channel) for large muscles like the quadriceps and hamstrings does not feel like it works the muscle as completely as 4 electrodes (2 channels) on each. However, this depends on the size of the person, how many channels you have available, and how many muscles you want to work at once. Large electrodes are more comfortable than small ones because they lessen the current density going through your skin. Rubber carbon electrodes last a lot longer than sticky gel electrodes, but you do need straps to hold them in place. In my opinion stick on gel electrodes are more trouble than they are worth. Rubber carbon electrodes wet with water and held with good straps feel better, work better, and last a lot longer. I’ve tested all sizes and 4” round rubber carbon electrodes are my favorite type and size. A 4” wide elastic-velcro strap is best to hold them in place.
Thanks for reading my blog. If you have any questions or comments (even hostile ones) please don’t hesitate to ask/share. If you’re reading one of my older blogs, perhaps unrelated to neck or back pain, and it helps you, please remember SpineFit Yoga for you or someone you know in the future.
Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.
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