wong1986

High Voltage Versus Low Voltage Electrical Stimulation
Force of Induced Muscle Contraction and Perceived
Discomfort in Healthy Subjects
RITA A. WONG
Key Words: Electric stimulation, Muscle contraction, Muscles.
Research findings support the use of electrical neuromuscular stimulation for several treatment goals: 1) strengthening
atrophied muscle or minimizing disuse atrophy,1-6 2) facilitating muscle reeducation,6-9 3) maintaining range of motion
and decreasing joint contractures,1,4,10 4) inhibiting spasticity,11-14 and 5) providing orthotic support to a joint. 71516 All
of the supportive research, however, is based on the use of
low voltage neuromuscular stimulation (LVNMS), which has
a maximum voltage output of less than 150 V, pulse duration
capabilities in the microsecond range, and either a monophasic or a biphasic waveform. 17
High voltage pulsed galvanic stimulation (HVPGS) is a
relatively new form of neuromuscular stimulation that typically uses voltages between 100 and 500 V, a twin-peaked
monophasic waveform, and a pulse duration of up to 200
µsec.18 The HVPGS technique is purported to fulfill all of the
treatment goals fulfilled by LVNMS, except for its limited
functional usefulness for providing orthotic support.17,19 This
limitation results because of the physical size of HVPGS units,
not because of their stimulation capabilities. The HVPGS
units currently in use are too large to be carried easily in one
hand during gait activities or clipped to a waist belt, an
important feature for use as a lower extremity orthotic device.
Although high voltage pulsed galvanic stimulation is a term
used frequently to specify the type of high voltage current that
I used in this study,18,20 other terminology (ie, high voltage
Ms. Wong is Assistant Professor of Physical Therapy, University of Connecticut, School of Allied Health Professions, Box U-101, 358 Mansfield Rd,
Storrs, CT 06268 (USA).
This research was funded by the University of Connecticut Research Foundation, Grant No. 1171-000-2402-35-019.
This article was submitted June 4, 1985; was with the author for revision 11
weeks; and was accepted December 5, 1985.
Volume 66 / Number 8, August 1986
pulsating direct current19 and high voltage interrupted direct
current17) also is used. Controversy exists regarding the use of
the term "galvanic" to describe a current with short pulse
duration because of the traditional association of galvanic
current with either uninterrupted ion flow or flow interrupted
only after a very long pulse duration.21 The use in this article
of the term high voltage pulsed galvanic stimulation, however,
is consistent with the operational definition approved by the
American Board of Physical Therapy Specialties (formerly
the Board of Certification of Advanced Clinical Competence
in Physical Therapy).22
Recent electrotherapy texts and HVPGS manuals suggest
that HVPGS is superior to LVNMS in two respects: comfort
and depth of penetration.17,18 The decreased discomfort of
HVPGS is attributed to its very short pulse duration and low
average current.17 Its deeper penetration is purportedly a
function of its high peak current.17,18 The deeper penetration
should affect more motor units, thereby inducing a stronger
contraction than LVNMS, which has a much lower peak
current. An extensive literature review, however, revealed no
research documentation that HVPGS either is less uncomfortable or results in a stronger contraction than LVNMS.
Clearly, objective documentation is needed on this subject.
The purpose of this study, therefore, is to compare HVPGS
to LVNMS in terms of the strength of an induced muscle
contraction and perceived discomfort. The null hypothesis
that was tested stated that no significant differences exist
between LVNMS and HVPGS for the following three dependent measures: 1) the foot-pounds of torque produced by
an electrically induced isometric contraction, 2) the perceived
discomfort associated with each type of stimulation, and 3)
subjective preference of treatment.
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High voltage pulsed galvanic stimulation (HVPGS) and low voltage neuromuscular
stimulation (LVNMS) techniques were compared for peak torque of an induced
isometric contraction, perceived discomfort, and subjective preference of treat­
ment. The high voltage current used a 40-µsec monophasic waveform, and the
low voltage current used a 300-µsec biphasic waveform. Both currents used a
pulse rate of 50 pps. Both HVPGS and LVNMS were administered to one muscle
group, either knee extensors or plantar flexors, of 24 healthy subjects. An
isokinetic dynamometer was used to assess peak torque. The perceived discom­
fort experienced with each type of electrical stimulation was quantified by the
use of a visual analog scale. For all dependent measures, data first were analyzed
for the whole treatment group and then analyzed for each subgroup. Correlated
t tests for the whole group and the plantar flexor muscle subgroup demonstrated
that 1) HVPGS produced a significantly greater average peak force of muscle
contraction than LVNMS and 2) HVPGS was perceived to be significantly less
uncomfortable than LVNMS. No significant differences were found between
treatments in the knee extensor muscle subgroup for these dependent variables.
Chi-square analysis revealed a subject preference for HVPGS in the whole group
and in both subgroups. This study indicates that HVPGS can produce a stronger,
less uncomfortable, induced isometric muscle contraction than LVNMS.
METHOD
Subjects
Equipment and Materials
I used a Respond® II neuromuscular stimulator* (Model
3128) to provide LVNMS and a Dynamax II stimulator† to
provide HVPGS. The specific characteristics of the waveform
used in this study are summarized in Table 1. The electrodes
provided by the manufacturer of each unit were used, although they required adjustment because their sizes and
shapes differed. Alon recently demonstrated that electrode
size is an important factor in determining the strength of a
muscle contraction.23 The LVNMS electrodes, therefore, were
cut, and portions of the stimulating surfaces of the HVPGS
electrodes were covered with nonconductive tape so that the
stimulating surface of the rectangular LVNMS and circular
HVPGS electrodes were equal in shape and size, about 40
cm2. Neuromod transcutaneous electrical nerve stimulation
electrode gel* was used as the conducting medium. For the
HVPGS treatment, the 500-cm2 dispersive electrode provided
by the manufacturer was used.
Isometric muscle contraction peak torque was measured
with a Cybex® II isokinetic dynamometer‡ and recorded with
a dual-channel strip chart recorder.‡ The Cybex® UpperBody-Exercise and Testing (UBXT ) table‡ and the Cybex®
Super-Heavy-Duty (SHD) Exertest tablet were used to maintain the subject's right lower extremity in the desired testing
position. At the beginning of each testing day, the dynamometer was calibrated according to the manufacturer's instructions.24
The perceived pain intensity associated with the use of each
form of electrical stimulation was evaluated with a visual
analog scale (VAS), a 10-cm horizontal line with distinct 1cm demarcations at each end. The left end of the line represented "no pain at all" and the right end represented "the
worst pain imaginable." The procedures for using this scale
are described in the next section. The reliability and validity
of this scale for evaluating the subjective perception of pain
intensity is well documented.25-27 Price et al have validated
the use of ratio-level comparisons with the VAS.25
Procedures
Each subject was treated twice, usually on consecutive days.
During each treatment visit, the subjects received HVPGS
and LVNMS, sequentially and randomly, using the device
settings summarized in Table 1. Additionally, the subjects
were divided randomly into two subgroups: all testing was
* Medtronic, Inc, Neuro Division, 6951 Central Ave NE, PO Box 1250,
Minneapolis, MN 55440.
† J A Preston Corp, 60 Page Rd, Clifton, NJ 07012.
‡ Cybex, Div of Lumex, Inc, 2100 Smithtown Ave, Ronkonkoma, NY 11779.
1210
Stimulation
Characteristic
Pulse rate
Duty cyclea
Rampb
Intensity
Pulse duration
Waveform
HVPGS
LVNMS
50 pps
10 sec on, 10 sec off
2sec
subject's maximum
tolerance
40 µsec
twin-peaked monophasic
50 pps
10 sec on, 10 sec off
2 sec
subject's maximum
tolerance
300 µsec
asymmetrical bi­
phasic
a
Length of each "on" and "off" time period of an interrupted current.
Length of time for current to rise gradually to preset intensity at
the beginning of each on portion of the duty cycle.
b
performed on the knee extensor muscles of the 10 subjects in
one subgroup, and all testing was performed on the plantar
flexor muscles of the 12 subjects in the other subgroup. Two
muscle groups were tested to ensure that the results obtained
were not simply a function of one particular muscle group.
Immediately before the first treatment session began, two
electrode placement points were located using the following
techniques. With a 2-pps stimulation, the hand probe of the
HVPGS unit was moved slowly over the anterior thigh or calf
(dependent on subgroup assignment) until the two points
yielding the greatest contraction of the assigned muscle group,
with the least co-contraction of the surrounding muscles, were
located. These points were marked with ink and, if necessary,
excessive hair was removed from them. One treatment electrode was then attached to each of these two treatment sites
using electrode gel and skin-tape patches in preparation for
the first treatment session. For the HVPGS treatment, an
additional large dispersive electrode was placed on the subject's mid-to-low back area.
During the first treatment visit, perceived discomfort and
subjective preference of treatment were measured using the
following procedures. The subjects received two random sixminute treatments, one with HVPGS and one with LVNMS.
During the first four minutes of each treatment, the intensity
of the current was increased gradually to each individual's
subjective maximum-tolerance level. The subjects were instructed:
The intensity will be increased slowly until you request that it
be stopped. I would like you to allow the intensity to be
increased until you reach the level you consider to be your
"maximum" tolerance. The stimulation will be cycling on and
off at 10-sec intervals for six minutes in total. The sensation
should be strong but bearable.
Each subject told the investigator when to stop increasing
the intensity (ie, when the sensation was too uncomfortable).
No attempt was made to encourage the subjects to accept or
reject more current than they requested. Immediately after
the first six-minute stimulation session, the subjects were
shown a VAS and were read the following directions:
The far left-hand side of this line represents "no pain at all";
the farright-handside of this line represents "the worst pain
imaginable." Consider the discomfort you felt from this treatment. Place a mark at the point on the line that you believe
represents the amount of discomfort you felt during this treatment.
PHYSICAL THERAPY
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Twenty-four subjects (9 men and 15 women) between 19
and 35 years of age ( = 24 years) and with no known
neurological or orthopedic dysfunction affecting the right
lower extremity participated in this study. The subjects refrained from vigorous exercise for two hours before testing.
This study was approved by the institutional research review
committee. The subjects signed informed consent forms before participation.
TABLE 1
Electrical Characteristics of the High Voltage Pulsed Galvanic
Stimulation (HVPGS) and Low Voltage Neuromuscular
Stimulation (LVNMS)
RESEARCH
TABLE 2
Peak Induced Torque and Visual Analog Scale (VAS) Values for
High Voltage Pulsed Galvanic Stimulation (HVPGS) and Low
Voltage Neuromuscular Stimulation (LVNMS)
Data Analysis
LVNMS
HVPGS
proper force transmission through the footplate. The Cybex®
II procedural manual notes that during voluntary plantar
flexion the intrinsic muscles of the foot contract to hold the
foot firmly against the footplate.24 During pilot testing, we
noted that the electrically induced plantar flexion contraction
was not accompanied by contraction of the intrinsic muscles
of the foot, thus, allowing the heel to lift off of the footplate
when standard procedures were implemented. Additional stabilization, therefore, was provided to maintain proper foot
contact with the footplate. The subject's right foot was covered
with a sock and then placed into a heel cup molded to fit over
the back of the footplate. The molded heel cup held the foot
in about 16 degrees of inversion. The subject's right foot and
ankle then were taped and strapped securely to the footplate.
Care was taken not to tape over the Achilles tendon. The
ankle was positioned in 5 to 7 degrees of plantar flexion and
the speed selector was set at 0°/sec.
The same stimulation points, electrical characteristics (Tab.
1), and method of administering the treatments that were
used during the first treatment visit also were used during the
second treatment visit. During the first four minutes of treatment, the current intensity was increased slowly during the
"on" portion of the duty cycle to the maximum level tolerated
by the subject. The subjects were told that the sensation should
be "as strong as you can tolerate for a 10-minute period of
time. You are to relax and let the machine do the work." The
HVPGS treatment and the LVNMS treatment each required
10 minutes to complete and were spaced 20 minutes apart.
The dynamometer's recorder was set at a speed of 5 mm/sec
throughout each 10-minute testing session. In all instances,
the same investigator applied the electrodes, controlled the
intensity, and gave the instructions to the subject.
Subject
Subgroup
Torque
(ft∙lba)
VAS
(cm)
Torque
(ft∙lb)
VAS
(cm)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Eb
Eb
E
E
E
E
E
E
E
E
Pc
P
P
P
P
P
P
P
P
P
P
P
5.8
4.8
13.5
12.2
7.0
12.9
0.0
8.9
3.2
14.7
15.0
14.9
24.6
11.6
15.3
8.0
21.8
9.6
10.8
25.7
22.6
1.6
12.0
7.1
2.2
1.0
2.5
3.0
1.5
0.7
5.1
1.7
0.0
0.6
0.6
0.6
0.1
6.7
3.0
0.2
1.6
1.0
0.8
0.5
3.0
3.1
1.8
1.7
10.4
2.0
0.6
3.4
1.8
7.2
5.2
7.9
0.1
14.4
23.8
13.3
17.7
7.0
14.2
0.6
10.0
7.1
7.1
20.8
13.8
0.5
8.5
6.9
3.0
1.9
3.3
4.2
2.5
1.8
1.8
2.6
0.0
1.6
4.4
3.9
1.8
7.5
2.0
0.0
2.3
0.4
3.9
1.2
2.9
4.9
2.6
1.7
Using the Statistical Package for the Social Sciences, I used
a two-tailed correlated Student's t test to analyze the mean
values and the standard deviations from the means for two of
the dependent measures: perceived discomfort and peak
torque. Perceived discomfort values were calculated by measuring the distance, in centimeters, from the left margin (zero
point) of the VAS to the subject's marking (subjective perception of pain intensity) using a standard metric ruler.
For the data analysis, peak torque was defined as the average
of the peak isometric forces produced during each 10-second
on cycle between minute 6 and minute 10 during the peak
torque assessment. The peak torque during each on cycle was
determined from the strip chart recording using the Cybex®
11 chart data card‡ to calculate the stylus deflection from the
baseline. Treatment preference was analyzed using the chisquare statistical test.29
RESULTS
1 ft∙lb = 1.356 N∙m.
E = knee extensor muscle subgroup.
c
P = plantar flexor muscle subgroup.
Two subjects were excluded from the data analysis. One
subject, although having no known neurological or orthopedic
dysfunction, demonstrated normal sensory and motor responses to LVNMS but exhibited no motor response and very
little sensory response to HVPGS, even though the current
intensity was increased to its highest point (ie, 500 V). This
pattern of response was suggestive of early peripheral neuropathy. Further inquiry revealed that this subject was an insulindependent diabetic, and subsequent evaluation by a neurolo-
Volume 66 / Number 8, August 1986
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s
a
b
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The subjects then marked the scale.
The same treatment procedures were performed then using
the second stimulator with the electrodes attached to the same
stimulation points. Immediately after this second treatment
session, the directions for using the VAS were repeated. The
subjects then marked a second VAS without seeing their first
scale marking.
At the end of the first treatment visit, after both types of
stimulation had been applied, the subjects were asked to
choose one of the following three statements: 1) preferred
treatment one, 2) preferred treatment two, or 3) no preference.
This completed the first treatment visit.
The purpose of the second treatment visit, usually conducted the next day, was to determine the average peak force
of isometric contractions produced by HVPGS and LVNMS.
For this treatment visit, the subjects were positioned according
to the following descriptions. Joint angle position was assessed
with a standard universal goniometer using bony landmarks
identified by Cole and Tobis.28
Knee extensor muscle subgroup. Each subject was seated
on the SHD table according to the manufacturer's guidelines
and stabilized with thigh and pelvic straps.24 The knee was
placed at 25 to 30 degrees of flexion and the speed selector
was set at 0°/sec.
Plantar flexor muscle subgroup. Each subject was positioned prone on the UBXT according to the manufacturer's
guidelines, with additional foot-and-ankle stabilizations for
TABLE 3
Average Visual Analog Scale Values After High Voltage Pulsed
Galvanic Stimulation (HVPGS) and Low Voltage Neuromuscular
Stimulation (LVNMS) for All Subjects and Two Subgroups
Group
Whole group (N = 22)
Plantar flexor muscle
subgroup (n = 12)
Knee extensor muscle
subgroup (n = 10)
a
HVPGS
(cm)
LVNMS
(cm)
s
s
t
Pa
1.8
1.7
2.6
1.7
2.44
.02
1.9
1.9
2.9
2.1
2.3
.04
1.8
1.5
2.3
1.1
1.05
NS
significant at p < .05.
TABLE 4
Average Peak Torque Values During High Voltage Pulsed
Galvanic Stimulation (HVPGS) and Low Voltage Neuromuscular
Stimulation (LVNMS) for All Subjects and Two Subgroups
Group
Whole group (N = 22)
Plantar flexor muscle
subgroup (n = 12)
Knee extensor muscle
subgroup (n = 10)
a
b
1 ft.lb = 1.356 N.m.
Significant at p < . 05.
1212
HVPGS
(ft.lba)
LVNMS
(ft.lb)
s
s
t
Pb
12.0
7.1
8.5
6.9
3.08
.006
15.1
7.4
11.3
7.3
2.55
.03
8.3
4.9
5.3
4.7
1.70
NS
TABLE 5
Summary of Chi-Square Analysis of Subject Preference for
Either High Voltage Pulsed Galvanic Stimulation (HVPGS) or
Low Voltage Neuromuscular Stimulation (LVNMS) for All
Subjects and Two Subgroups
Subjects
Whole group
(N = 22)
Plantar flexor
muscle
subgroup
(n = 12)
Knee extensor
muscle
subgroup
(n = 10)
Preferred
HVPGS
Preferred
LVNMS
No
Preference
SS
Oa
Eb
O
E
O
E
18
7.33
2
7.33
2
7.33
23.29c
9
4.0
1
4.0
2
4.0
9.5d
9
3.3
1
3.3
0
3.3
14.75a
a
Observed.
Expected = number of subjects in sample group divided by three
(number of possible choices).
c
p<.005.
b
d
e
p<.01.
p<.005.
DISCUSSION
For the whole group and the plantar flexor muscle
subgroup, the findings of this study support the theoretical
assumptions that HVPGS can produce a stronger muscle
contraction and is less uncomfortable than LVNMS. The
knee extensor muscle subgroup, however, did not demonstrate significant differences in either peak torque or perceived
discomfort. The reason for thisfindingis unclear. One possible explanation may be that the final sample size (n = 10) of
the knee extensor muscle subgroup was too small. Another
possible explanation may be that proximal structures contain
fewer sensory receptors than do distal structures.30 An individual, therefore, may be less able to discriminate between
subtle differences in painful stimuli when they are applied to
the thigh, rather than to the calf. This diminished sensory
capability could result in less divergent values for perceived
discomfort. Because the maximum intensity of current applied to the muscle groups for each type of electrical stimulation was based on perceived discomfort (ie, each subject
determined when the sensation became intolerable), less divergence also could be expected between induced torque
values for the knee extensor muscle subgroup. The data
summarized in Table 2 support the latter explanation. The
divergence between the HVPGS and LVNMS values for the
subjects in the knee extensor muscle subgroup were less
pronounced than for the subjects in the plantar flexor muscle
subgroup, although the responses of both subgroups were
similar. This finding raises a potentially important question
regarding limitations of the ability to generalize electrical
stimulation research findings from one muscle group to another, especially when perceived discomfort is a factor.
The subjective preference data demonstrated that the majority of the subjects in both subgroups preferred the sensation
of HVPGS over LVNMS. This is an important finding,
especially when combined with the fact that a stronger conPHYSICAL THERAPY
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gist confirmed that a mild peripheral neuropathic condition
did exist in his lower extremities.
A second subject was excluded from the data analysis
because the electrically induced muscle force recorded on the
subject's strip chart may have been contaminated with voluntarily induced force. In all of the other subjects, a clear
distinction was recorded between the "off" cycle (ie, stylus
returns to baseline) and the on cycle (ie, stylus deflects from
baseline). The recorded muscle force was almost constant
when this subject was tested. Short bursts of high peak torques
that did not appear to be related to electrical stimulation also
were present. The total number of subjects included in the
data analysis, therefore, was 22.
Table 2 lists the VAS values and peak torque values of each
subject. Table 3 summarizes the results of the correlated t-test
analysis for the VAS values, and Table 4 summarizes the
results of the correlated t-test analysis for the peak torque
values. The HVPGS technique was found to be significantly
less uncomfortable than LVNMS for the group as a whole (p
< .02) and for the plantar flexor subgroup (p < .04). The
HVPGS technique resulted in a significantly stronger muscle
contraction than did LVNMS for the group as a whole (p <
.006) and for the plantar flexor muscle subgroup (p < .03).
No significant differences were found in the VAS or peak
torque values for the knee extensor muscle subgroup.
The results of the chi-square analysis for subject preference
are summarized in Table 5. The group as a whole and both
subgroups preferred HVPGS over LVNMS.
RESEARCH
Volume 66 / Number 8, August 1986
Elapsed Time (min)
Figure. Average peak torque induced by high voltage pulsed galvanic
stimulation (HVPGS) and low voltage neuromuscular stimulation
(LVNMS) for the whole group, recorded at 1-minute intervals between
minutes 5 and 10 of the peak torque assessment session.
rounding muscles. Contraction of stabilizing or antagonistic
muscles simultaneously with that of the agonistic muscles
(knee extensors or plantar flexors) would result in more than
one force vector active at the joint being tested; therefore, the
force being transmitted through the dynamometer would
reflect the agonistic forces minus all opposing forces, not the
agonistic forces alone. Despite careful electrode placement,
some subjects experienced palpable contractions of surrounding muscles during the electrical stimulation that became
more pronounced as the intensity was increased. These cocontractions were more common in the knee extensor muscle
subgroup than in the plantar flexor muscle subgroup.
This study demonstrates that further research is needed in
several related areas:
1. Although "typical" electrical characteristics were used, the
use of these electrical stimulators at different frequencies,
pulse widths, duty cycles, or waveforms may result in
dissimilar findings. Further studies using other electrical
characteristics are needed.
2. Although this study documented the initial responses of
subjects to HVPGS and LVNMS, it did not assess responses that may result with increased exposure to those
types of electrical stimulators. Replications of this study
based on additional electrical stimulation sessions conducted before the assessment of induced torque and perceived discomfort values, thus allowing the subjects to
adjust to the electrical stimulation experience, might yield
useful data. This format also might result in documentation to support or refute the hypothesis that subjects are
able to tolerate increased levels of current as they become
more familiar with the treatment procedures and equipment.
3. Replications of this study using subjects with various diseases or limitations are needed to determine whether factors such as preexisting painful conditions or muscle atrophy will suppon or refute the findings of this study.
4. This study suggests that the magnitude of the response to
electrical stimulation for both perceived discomfort and
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traction generally was associated with HVPGS. Patient tolerance and acceptance are important considerations in the
effective application of electrical stimulation. This finding
justifies the need for further investigation of the clinical
applicability of HVPGS.
Two interesting findings of this study are the relatively low
perceived discomfort and peak torque values. The perceived
discomfort values (Tab. 3), indeed, are lower than might be
expected considering that the subjects were instructed to allow
the current to be increased to the highest tolerable level. That
this study assessed each subject's perceived discomfort during
the initial exposure to electrical stimulation probably is the
major reason for the relatively low perceived discomfort values. In my experience, many individuals initially are fearful
of having electricity used on them. This fear' may result in
subjects initially limiting their tolerance of electrical current
to a level that they consider to be "safe." Indeed, the electrotherapy literature advises that the patients' fear of electricity
must be overcome for the current to be increased sufficiently
for effective treatment.17,21,31 The use of the VAS, a measure
of pain intensity rather than of the emotional components of
the pain experience, during a subject's initial electrical stimulation treatment session may identify any hesitancy that may
exist to tolerate the maximum level of pain intensity.27
The relatively low peak torque values in this study probably
are related to the following procedures that were implemented
to ensure maximal consistency in the application of HVPGS
and LVNMS:
1. Relatively small electrodes were used. Alon has demonstrated that large electrodes result in significantly greater
induced torque values than do small electrodes.23
2. Only two electrodes were used. Benton et al described
application techniques using both two and three electrodes
for both the knee extensor and plantar flexor muscle
groups.21 They reported that three electrodes usually will
induce a stronger muscle contraction than two electrodes
when applied to either the knee extensor or plantar flexor
muscles.
3. The assessment of peak torque was performed after only
one previous application of each type of electrical stimulation when the subjects' fear of electricity probably was
still a factor in their acceptance of the electrical stimulation
treatments.
4. The intensity of the current was increased only during the
first 4 minutes of the 10-minute treatment session. Several
subjects commented that they probably could have tolerated more current toward the end of the 10-minute treatment session. Those subjects possibly accommodated gradually to the electrical stimulus; that is, the nerve became
less responsive when activated by this repetitive stimulus.31
This gradual accommodation would result in lower sensory
and motor responses.21 Indeed, average torque values decreased slightly between minute 5 and minute 10, as depicted in the Figure. Although fatigue cannot be eliminated
as a possible explanation for the decrease in torque values
over time, it is an unlikely possibility. The low torque
values, combined with the brief stimulation period (10minute on-off cycling treatment), are not consistent with
the rapid fatigue of normal muscle.21 Accommodation is a
more likely explanation.
Another possible explanation for the low torque recordings
is that co-contractions were induced electrically in the sur-
peak torque may differ based on the muscle group being
tested. This factor should be investigated further.
5. Further investigation is needed into the validity of dynamometry to measure maximum muscle force generated by
a given muscle during an electrically induced contraction.
CONCLUSIONS
REFERENCES
1. Munsat TL, McNeal DR, Waters RL: Preliminary observations on prolonged
stimulation of peripheral nerve in man. Arch Neurol 33:608-617, 1976
2. Peckham PH, Mortimer JT, Marsolais EB: Alteration in the force and
fatigability of skeletal muscle in quadriplegic humans following exercise
induced by chronic electrical stimulation. Clin Orthop 114:326-334, 1976
3. Merletti R, Zelaschi F, Latella D, et al: A control study of muscle force
recovery in hemiparetic patients during treatment with functional electrical
stimulation. Scand J RehabH Med 10:147-154, 1978
4. Winchester P, Montgomery J, Bowman BR, et al: Effects of feedback
stimulation training and cyclical electrical stimulation on knee extension in
hemiparetic patients. Phys Ther 63:1096-1103, 1983
5. Fournier A, Goldberg M, Green B, et al: A medical evaluation of the effects
of computer-assisted muscle stimulation in paraplegic patients. Orthopedics 7:1129-1133, 1984
6. Baker LL, Parker K, Sanderson D: Neuromuscular electrical stimulation for
the head-injured patient. Phys Ther 63:1967-1974, 1983
7. Liberson WT, Holmquest HJ, Scott D, et al: Functional electrotherapy:
Stimulation of the peroneal nerve synchronized with the swing phase of
gait of hemiplegic patients. Arch Phys Med Rehabil 42:101-105, 1961
8. Waters RL, McNeal DR, Perry J: Experimental correction of footdrop by
electrical stimulation of the peroneal nerve. J Bone Joint Surg [Am]
57:1047-1054,1975
9. Bowman BR, Baker LL, Waters RL: Positional feedback and electrical
stimulation: An automated treatment for the hemiplegic wrist. Arch Phys
Med Rehabil 60:497-502, 1979
10. Baker LL, Yeh C, Wilson D, et al: Electrical stimulation of the wrist and
fingers for hemiplegic patients. Phys Ther 59:1495-1499, 1979
11. Mooney V, Wileman W, McNeal DR: Stimulator reduces spastic activity.
JAMA 207:2199-2200, 1969
12. Liberson WT: Experiment concerning reciprocal inhibition of antagonists
elicited by electrical stimulation of agonists in a normal individual. Am J
Phys Med 44:306-308, 1965
13. Dimitrijevic MR, Nathan PW: Studies of spasticity in man: 5. Dishabituation
of the flexion reflex in spinal man. Brain 94:77-90, 1971
14. Fulbright JS: Electrical stimulation to reduce chronic toe-flexor hypertonicity. Phys Ther 64:523-525, 1984
15. Malezic M, Stanic U, Kljajic M, et al: Multichannel electrical stimulation of
gait in motor-disabled patients. Orthopedics 7:1187-1195, 1984
1214
16. Griethuysen CM, Day GA: Biomechanical analysis of patient using FES
peroneal brace and further developments. Orthopedics 7:1196-1200, 1984
17. Wolf SL (ed): Electrotherapy. New York, NY, Churchill Livingstone Inc.
1981, pp 14-22
18. Newton RA: Electrotherapeutic Treatment: Selecting Appropriate Waveform Characteristics. Clifton, NJ, J A Preston Corp, 1984
19. Alon G: High Voltage Stimulation (High Voltage Pulsating Direct Current).
Chattanooga, TN, Chattanooga Corp, 1984
20. Newton RA, Karselis TC: Skin pH following high voltage pulsed galvanic
stimulation. Phys Ther 63:1593-1596, 1983
21. Benton LA, Baker LL, Bowman BR, et al: Functional Electrical Stimulation:
A Practical Clinical Guide, ed 2. Downey, CA, Rancho Los Amigos Rehabilitation Engineering Center, 1981, pp 72-73, 88-97
22. Physical Therapy Advanced Clinical Competencies: Clinical Electrophysiology. Chapel Hill, NC, Clinical Electrophysiotogy Specialty Council, Board
for Certification of Advanced Clinical Competence, 1984
23. Alon G: High voltage stimulation: Effects of electrode size on basic excitatory responses. Phys Ther 65:890-895, 1985
24. Isolated-Joint Testing and Exercise: A Handbook For Using Cybex® II and
UBXT. Ronkonkoma, NY, Cybex, Div of Lumex, Inc. 1981, pp 67-70, 7376
25. Price D, McGrath P, Rafii A, et al: The validation of visual analog scales as
ratio scale measures for chronic and experimental pain. Pain 17:45-56,
1983
26. Revill S, Robinson J, Rosen M, et al: The reliability of a linear analog for
evaluating pain. Anaesthesia 31:1191-1198, 1976
27. Ohnhaus E, Adler R: Methodological problems in the measurement of pain:
A comparison between the verbal rating scale and the visual analog scale.
Pain 1:379-384, 1975
28. Cole TM, Tobis JS: Measurement of musculoskeletal function. In Kottke
FJ, Stillwell GK, Lehmann JS (eds): Krusen's Handbook of Physical Medicine and Rehabilitation, ed 3. Philadelphia, PA, W B Saunders Co, 1982,
pp 30-31
29. Duncan RC, Knapp RG, Miller MC: Introductory Biostatistics for the Health
Sciences. New York, NY, John Wiley & Sons Inc. 1977, pp 139-142
30. Williams PL, Warwick R: Functional Neuroanatomy of Man. Philadelphia,
PA, W B Saunders Co, 1976, pp 1164-1165
31. Mannheimer JS, Lampe GN: Clinical Transcutaneous Electrical Nerve
Stimulation. Philadelphia, PA, F A Davis Co, 1984, p 221
PHYSICAL THERAPY
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Within the limitations of this study, the following conclusions may be stated:
1. The HVPGS technique induced a stronger isometric muscle contraction than did LVNMS, one that was more
pronounced during plantar flexion than during knee extension.
2. The HVPGS technique was perceived by subjects to be
significantly less uncomfortable than LVNMS. Relatively
less discomfort also was experienced during plantar flexion
than during knee extension.
3. The HVPGS technique was preferred by subjects significantly more often than LVNMS.