Monday, February 20, 2017

E-Stim:What is it Good For?

Electrical Stimulation: An Overview

If you have spent time in physical therapy while rehabilitating an injury, you may have experienced electrical stimulation, or “E-stim”. Patients are not always fully aware of the implications or purpose of the electrical stimulation, and so what follows is a brief introduction to inform you as to why your physical therapist may suggest that electrical stimulation to be an important intervention during the rehabilitation process.

There are different forms of electrical stimulation
(or “E-stim”) that serve a variety of functions. Perhaps the most well-known use of E-stim is for pain control. When E-stim is used for pain control, it is commonly referred to as TENS (transcutaneous electrical nerve stimulation). TENS is often utilized post-sessions to reduce joint or muscle pain; electrodes are placed at or around the site of pain to stimulate joint receptors and override the pain signal. This can especially important for individuals with osteoarthritis, back pain, or for patients in rehab following a surgery. One study reports that although TENS will not speed up or alter the longterm outcomes after shoulder surgery, the use of TENS has been shown to decrease opioid use in the first 72 hours and help to control postoperative pain (Thigpen et al). With the overdosing of narcotics and opioids to control pain in modern society, TENS is likely an underutilized alternative to pain management.

One key to maximizing the pain-relieving benefits of TENS is in the intensity of the signal. Studies indicate that the intensity should be turned at a level 3x the sensory threshold. What this means is that if you start to feel a tingle at 10mA (milliamp), you will gain the greatest pain relief if the treatment is turned up to 30mA. You may also notice that after a few minutes into a TENS session, the signal does not feel as strong. You may worry that you are no longer gaining the same benefit. However, it has been shown that although your perception of the signal may change, the activation of your sensory nerve fibers does not change (Pietrosimone et al). So if it feels stronger in the beginning, but less intense after a few minutes, you are still gaining the same pain-relieving benefit!

Another common function of electrical stimulation is for strengthening muscle, when it is known as NMES (neuromuscular electrical stimulation). “Isn’t that what the exercise is for?” you say. Absolutely! However, in order to understand why NMES is so helpful for strengthening, let’s take a look at one basic principle of strength training, the recruitment principle. The boiled down version of this rule says that when you strength train at low intensity (lifting light weights) or are doing aerobic exercise (walking), you are using your type 1 muscle fibers. When you are completing intense exercise (lifting heavy weights or with fast jogging/sprinting), you first recruit those same type 1 fibers, and then type 2a, and finally type 2 b fibers. So in order to get full benefit from strength training, you generally have to work extra hard in order to recruit all your muscle fibers. However, NMES skips right to the chase for you. It utilizes ‘’random recruitment’’ which means it automatically recruits all 3 muscle fiber types. How does this affect strengthening? For one, it results in increased pennation angle of fibers so that you can fit more contractile proteins in parallel throughout the muscle (Gondin, 2005). Let’s take a look at one study following ACL reconstruction.

When studying strength recovery of the quadriceps 6 weeks after ACL surgery, two groups were compared. One group utilized NMES, the other group utilized voluntary exercise (normal exercise routine, no NMES). The results weren’t even close. The NMES group had restore their affected leg’s quadricep’s strength to 70% of the unaffected leg’ strength, while the voluntary exercise group had only recovered about 50% of the strength. Bottom line: NMES restored strength quicker, which translates into quicker recovery time.

NMES is also viable in strengthening older adults (>65 yrs). Stackhouse et al reported that when using NMES on fatigued muscles, there was a 16% stronger muscle contraction with using NMES vs voluntary strength training.

 A third use of e-stim is for restoring functional control of muscles (functional electrical stimulation). This option can be utilized for someone who is having trouble activating key muscles to perform a basic movement. For example, in a patient who has had a stroke may have difficulty bringing their toes up towards their nose (dorsiflexion), which can manifest as a falling hazard when walking. FES can be used to stimulate the muscles in charge of dorsiflexion when this patient is walking, resulting in improved voluntary control of these muscles over time and increased safety.
SUMMARY To recap, e-stim is used for a variety of purposes, the most common of which are: pain control (TENS), strengthening (NMES), and to improve functional capacity (FES). All 3 use variations in certain parameters including signal frequency, phase duration, and amplitude to accomplish what each patient needs. Talk to your physical therapist or ask questions you may have regarding this effective intervention.

Gondin, et al. Electromyostimulation Training Effects on Neural Drive and Muscle Architecture. Medicine & Science in Sports & Exercise, 2005, Volume 37(8) pp. 1291- 1299.

L Snyder-Mackler. Strength of the Quadriceps Muscle and Functional Recovery After Reconstruction of the ACL: A Prospective Clinical Trial of Electrical Stimulation. Journal of Bone and Joint Surgery Vol. 77A, No. 8: 1166-1173, 1995

Mizner, et al. Early Quadriceps Strength Loss After Total Knee Arthroplasty. J Bone Joint Surg, 2005. 87 (5): 1047-1053

Pietrosimone BG, et al. Effects of transcutaneous electrical nerve stimulation and therapeutic exercise on quadriceps activation in people with tibiofemoral osteoarthritis. JOSPT. 2011 Jan;41(1):4-12.

Stackhouse et al. Maximum Voluntary Activation in Nonfatigued and Fatigued Muscle of Young and Elderly Individuals Physical Therapy 81(5):1102-9 · May 2001

Thigpen, Charles A, et al. The American Society of Shoulder And Elbow Therapists’ consensus statement on rehabilitation following arthroscopic rotator cuff repair. Journal of Shoulder and Elbow Surgery. 2016. 25, 521-535.

Matthew J. Brennan PT, DPT
The Physical Therapy & Wellness Institute
 2456 W Main St. Norristown, PA 19403
 tel: (610) 630-0101 fax: (610) 630-1068