Combined neuromuscular electrical stimulation and transcutaneous electrical nerve stimulation for treatment of chronic back pain: a double-blind, repeated measures comparison. (1997)

INTERVENTIONS:
Subjects self-administered NMES, combined NMES/TENS, TENS, and placebo treatments. Each treatment had a duration of 5 consecutive hours per day over 2 consecutive days, with a 2-day hiatus between treatments to minimize carryover effects.
MAIN OUTCOME MEASURES:
Pain reduction was assessed through pretreatment to posttreatment differences on the Present Pain Intensity (PPI) scale, and a visual analogue scale of Pain Intensity (VAS-I). Posttreatment pain relief was assessed using a visual analogue scale of Pain Relief (VAS-R).
RESULTS:
Combined treatment, NMES, and TENS each produced significant pretreatment to posttreatment reductions in pain intensity as measured by both the PPI and VAS-I (p < .05). Combined treatment was superior to placebo on pain reduction (p = .001, p = .016) as well as pain relief (p < .001). Combined treatment was also superior to both TENS and NMES for pain reduction and pain relief (p < .01). NMES and TENS were superior only to placebo for pain relief (p < .001).
CONCLUSIONS:
Combined NMES/TENS treatment consistently produced greater pain reduction and pain relief than placebo, TENS, or NMES. NMES alone, although less effective, did produce as much pain relief as TENS. Although preliminary, this pattern of results suggests that combined NMES/TENS may be a valuable adjunct in the management of chronic back pain. Further research investigating the effectiveness of both NMES and combined NMES/TENS seems warranted.

Select quotes from the article:
“Research with animals suggests that NMES may reduce pain by stimulation of the release of endogenous analgesics as well as vasoactive substances affecting blood flow and possibly temperature. Its also possible that NMES reduces pain through muscle toning and prevention of disuse atrophy and the muscle degeneration frequently associated with chronic myofascial pain.”
“Group trends show that TENS was remarkably similar to placebo on every measure except the VAS-R, in addition to being inferior to both combined treatment and NMES on every measure. In contrast trends for NMES were in the direction of greater effectiveness than both placebo and TENS on every dependent measure.

TENS Parameters used:

• Waveform: asymmetrical biphasic square wave
• Duty Cycle: continuous
• Duration: 5 hour
• Rate: 100 hz
• Pulse Duration: 100 mS
• Intensity: machine max 60 mA, instructed “to an amplitude that produced comfortable tingling sensation”
• Training Frequency: 5 hours per day for 2 days

NMES Parameters used:

• Waveform: symmetrical biphasic
• Duty Cycle: 5s on 15s off
• Duration: 10 minutes
• Rate: 70 Hz
• Pulse Duration: 200 mS
• Intensity: 10 mA max, instructed “strong and perceptible, but not painful contractions of the muscle under each electrode”
• Training Frequency: 3 times in 5 hours with 130 minutes rest between, for 2 days

Chad’s comments:

This is a great study that nobody knows about, and every physical therapist should.

For the record, a lot of practitioners and I use the term “EMS” (electrical muscle stimulation) interchangeably with “NMES” (neuromuscular electrical stimulation), as the same currents used with the purpose of increasing muscle strength, while TENS (transcutaneous electrical nerve stimulation) being used with the intention of decreasing pain.

The combination group had the greatest reduction in pain, but that isn’t what intrigues me. What I find most interesting (because I find it in my physical therapy office as well) is that EMS currents did a better job at reducing pain than did the TENS currents. The study was only over 2 days, so that is not enough time for muscle strengthening to have an effect on pain; therefore, the greater effect of EMS has to be from the current itself. Most proponents of TENS cite gate control theory (which simply suggests that increasing general sensation to the brain inhibits the brain’s ability to detect pain) as being a large part of the reason pain is decreased with TENS. Gate control theory does seem to be holding up as legitimate over time, and what I think EMS does better than TENS is it uses much stronger stimulus. My way of thinking, which works great with my physical therapy patients (whether it be low back pain, neck pain, arthritic pain, or even headaches) is that if you are going to exploit gate control theory to reduce pain, EXPLOIT THE THEORY, which EMS does with overwhelming sensory input with intensities great enough to cause strong muscle contractions. The side with a benefit of EMS is that you get a two-for-one benefit of also increasing strength, which for most people (especially those in pain) is a pretty big benefit.

Also I shouldn’t ignore the primary finding of this study which was that the combined TENS and EMS was best overall, so I’ll have to think about that and how that can be best implemented in practice. I don’t think that just doing EMS solely to the muscles that hurt is ideal, nor do I think you should just anesthetize the body to pain with strong electrical currents all day long is ideal if doing so allows the patient to continue maladaptive behaviors that will lead to further physical decline. So like many things it is all about balance.