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Clinical Tests
Research results
Varying pulses help stimulate 'paralyzed muscles'
When Superman actor Christopher Reeve broke several
upper cervical vertebrae in a Virginia steeplechase
accident in 1995, he was paralyzed from the neck down,
and the prognosis was poor. Such devastating mishaps
are not uncommon.
Potential solutions have ranged from possible spinal
cord regeneration to use of bionics-with little real
success so far. But in the future, scientists such as
Stuart A. Binder-Macleod, physical therapy, say they
hope that such tragedies can be reversed, at least in
part, by artificial stimulation of the skeletal muscles.
In the April issue of the Journal of Neurophysiology,
Binder-Macleod, with doctoral candidate Samuel C.K.
Lee and undergraduates April D. Fritz and Lorin J. Kucharski,
explores the relationship between the induction of small
electrical shocks and the strength of progressively
fatigued leg muscle reactions in seven men and five
women who volunteered for a laboratory study. The paper,
titled New Look at Force-Frequency Relationship of Human
Skeletal Muscle: Effects of Fatigue, will add to the
medical literature that might someday help people such
as Reeve improve function.
"Electrical (muscle) stimulation is used for many
things by physical therapists. My research, in general,
tries to understand the relationship between stimulation
rate, the force the muscle produces and the fatigue
it induces," Binder-Macleod said.
In a typical situation, "we use a 20- or 30- or
40-pulse-per-second electrical stimulation to activate
a muscle," he explained. "But when the central
nervous system turns on a muscle it uses an irregular
frequency of pulses during activation. What we've tried
to do is look at the best pattern rather than the best
frequency...comparing forces produced over a large range
of different frequencies. These are really very brief
pulses of current. A microsecond is only a millionth
of a second, and each pulse might only last 600 microseconds,
just enough to activate the muscle, with a 'pulse train'
of maybe 10 pulses."
Binder-Macleod, who has been at UD 11 years, is an
associate professor and associate chair of the physical
therapy department. He earned a bachelor's degree in
physical therapy from the State University of New York
in Buffalo in 1974; a master's degree in medical science
from Emory University in Atlanta in 1979; and a doctorate
in physiology from the Medical College of Virginia in
Richmond in 1987.
Why use electrical stimulation on muscles? Binder-Macleod
cited several reasons. He points to the now common and
relatively simple heart pacemaker, which sends minuscule
"shocks" to the heart to maintain its rhythm.
"And, we use electrical stimulation to make muscles
in people with central nervous system problems functional,
for instance in someone who's had a stroke and whose
foot drags. You can put on an ankle brace, or you can
stimulate it so the foot lifts up when they walk. One
problem is that the muscles get tired more easily when
you activate them artificially," he said. "But,
there are certain functions of the central nervous system
that we don't understand," he added.
To help people such as Reeve, "the primary focus
of most of the research is to try to get them to stand
and walk by using electrical stimulation," Binder-Macleod
explained. But success has been limited, he said: "To
date, it has still not enjoyed widespread public acceptance.
There are important control problems... trying to get
the muscles to coordinate naturally. We're a very long
way away from getting someone like Reeve to stand up
and walk."
In conducting the study, the volunteers were seated
on a chair-like device, a dynamometer, with a seat belt.
The equipment is designed to measure muscle force, both
induced naturally by the subject or by electrical stimulation
of the muscles in the area of the knee, he said. To
measure reaction of the muscles, the subjects would
"try to straighten out their knee as hard as they
could," using the quadriceps femoris muscle on
the front of the thigh. "Then they just relaxed,
and we used electrical pulses to activate them to about
20 percent of maximum force," according to Binder-Macleod.
"We used a range of frequencies going from 8 pulses
per second to 100 pulses per second, and we used variable
frequency trains, with some (sets of pulses) closer
together than others, and we'd look at the force produced
in response to the stimulus," Binder-Macleod said.
"The basic results were very exciting," Binder-Macleod
explained. "With variable frequency trains we were
able to produce more force than with any constant frequency
trains. And it's the first study that shows this. No
one has ever done this before."
The study suggests that using electrical stimulation
with varying intervals, rather than regular intervals,
"may be useful during clinical applications of
electrical stimulation," according to his research.
The experiments described in the article are part of
a federally funded, five-year project through a $500,000
grant from the National Institutes of Health.
-Phil Milford
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