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
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.
References
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
ptwinstitute.com
The Physical Therapy & Wellness Institute
2456 W Main St. Norristown, PA 19403
tel: (610) 630-0101 fax: (610) 630-1068
ptwinstitute.com
