Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion
Circumferential pressure (CP) applied to the limb has been shown to decrease muscle activity in subjects without neuromuscular disorders and in individuals with a spinal cord injury and cerebrovascular accidents.
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Інститут фізіології ім. О.О. Богомольця НАН України
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irk-123456789-683262014-09-22T03:01:42Z Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion Agostinucci, J. Circumferential pressure (CP) applied to the limb has been shown to decrease muscle activity in subjects without neuromuscular disorders and in individuals with a spinal cord injury and cerebrovascular accidents. Було показано, що круговий тиск (КТ), прикладений до кінцівки, зумовлює зменшення м’язової активності в осіб без нервово-м’язових розладів і у пацієнтів з пошкодженнями спинного мозку й цереброваскулярними патологіями. 2010 Article Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion / J. Agostinucci // Нейрофизиология. — 2010. — Т. 42, № 1. — С. 35-43. — Бібліогр.: 43 назв. — англ. 0028-2561 http://dspace.nbuv.gov.ua/handle/123456789/68326 612.73:612.76 en Нейрофизиология Інститут фізіології ім. О.О. Богомольця НАН України |
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Circumferential pressure (CP) applied to the limb has been shown to decrease muscle activity in subjects without neuromuscular disorders and in individuals with a spinal cord injury and cerebrovascular accidents. |
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Agostinucci, J. Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion Нейрофизиология |
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Agostinucci, J. |
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Agostinucci, J. |
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Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion |
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Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion |
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Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion |
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Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion |
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Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion |
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effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion |
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Інститут фізіології ім. О.О. Богомольця НАН України |
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2010 |
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Effect of circumferential air-splint pressure on the soleus stretch reflex during a voluntary ramp plantar flexion / J. Agostinucci // Нейрофизиология. — 2010. — Т. 42, № 1. — С. 35-43. — Бібліогр.: 43 назв. — англ. |
| series |
Нейрофизиология |
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AT agostinuccij effectofcircumferentialairsplintpressureonthesoleusstretchreflexduringavoluntaryrampplantarflexion |
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2025-07-05T18:09:24Z |
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1836831436646121472 |
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НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 1 35
UDC 612.73:612.76
J. AGOSTINUCCI1
EFFECT OF CIRCUMFERENTIAL AIR-SPLINT PRESSURE ON THE SOLEUS
STRETCH REFLEX DURING A VOLUNTARY RAMP PLANTAR FLEXION
Received 25.11.09
Circumferential pressure (CP) applied to the limb has been shown to decrease muscle activity
in subjects without neuromuscular disorders and in individuals with a spinal cord injury and
cerebrovascular accidents. Thus far, studies estimating the CP efficacy with respect to reflex
excitability of motoneurons mainly used the H reflex technique on a resting muscle. The
purpose of our study, therefore, was to investigate the effect that CP exerts on the soleus stretch
reflex (SSR) when superimposed onto a voluntary ramp plantar flexion movement in subjects
without neuromuscular disorders. Forty-eight subjects volunteered for this study. SSRs were
investigated before, during, and after the application of pressure to the calf. An inflated
air-splint connected to a pressure transducer was used to administer and measure the pressure
set to 45-50 mm Hg. SSRs were elicited by dorsiflexing the subject’s ankle by 10 deg at
180 deg/sec, while the subject plantarflexed against a moving footplate at 20% of the maximum
voluntary contraction through a 30 deg arc at 90 deg/sec. Twenty-five SSRs were recorded
and averaged for each experimental phase; peak-to-peak amplitudes were measured and
normalized, and reflex latencies were also measured. Friedman Repeated Measures Analysis
of Variance on Ranks was used to analyze the differences in the SSR latency and amplitude
from the baseline values. No significant general difference in the SSR amplitude was found
during pressure application, although individual responses varied widely. The post-pressure
values returned to the baseline, and the differences were insignificant. The reflex latencies
were also unchanged with respect to the baseline levels. Thus, a CP inhibitory effect on reflex
excitability of motoneurons is mild, on average, and variable when a voluntary movement is
a condition. The CP technique may not be as efficacious in reducing muscle hyperactivity as
was previously thought.
Keywords: soleus stretch reflex, circumferential pressure, H reflex, ramp movement.
1 University of Rhode Island, Kingston, USA.
Correspondence should be addressed to J. Agostinucci
(e-mail: gusser@uri.edu).
INTRODUCTION
Many investigators have studied the effects of pressure
applied to the muscles on muscle reflex excitability,
in particular on the H reflex amplitude, and supposed
that such a technique can provide a significant effect on
the activity of motor segmental neuronal mechanisms.
Kukulka et al. [1], and Leone and Kukulka [2] studied
the application of continuous pressure over the Achilles
tendon. A decrease in the soleus H reflex amplitude was
demonstrated, but this decrease was short-lasting and
independent of the intensity of pressure applied [1, 2].
The duration of H reflex reduction by pressure applied
to the tendon correlated with the type of pressure
applied, with intermittent pressure providing longer-
lasting decreases than continuous pressure. Morelli
et al. [3, 4] showed that pressure from massage over
the mm. triceps surae also produced a short-duration
decrease in the H reflex. These results were reported
for subjects with both no history of neurological
disease (Snd) and cerebrovascular accidents (Scva)
[1-4].
Robichaud et al. further investigated the effects
of pressure by applying an air splint around the
calf and recorded the soleus H reflexes in Snd, Scva,
and subjects with spinal cord injuries [5, 6]. These
authors demonstrated a significant pressure-induced
H reflex depression that lasted within the entire time
when pressure was applied in all the three subject
groups. The amplitudes returned to baseline values
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 136
immediately after air pressure release. The authors
suggested that their results were partly due to the
technique of pressure administration. Pressure applied
by an air-splint exerts constant pressure stimulation
of cutaneous and muscle receptors of both agonist and
antagonist musculature (circumferential pressure),
thus causing longer-lasting H reflex inhibition, as
compared with other types of pressure administration,
such as massage or continuous/intermittent tendon
pressure [1-6].
The H reflex is an EMG manifestation of the
electrically elicited monosynaptic reflex [7-9].
Obtaining of this response is rather simple and
gives an estimation of the alpha motoneuron reflex
excitability (MNRE). It is an electrical equivalent
to the soleus stretch reflex (SSR) except it bypasses
muscle spindles and, therefore, does not take into
account the respective receptor influence [10-12].
The SSR has an advantage over the H reflex in that
it uses a more natural stimulus (physical stretch) to
elicit the reflex. The nature of this stimulus differs
in that it evokes a relatively desynchronized and
dispersed activation of Ia afferents, whereas electrical
stimulation used to evoke the H reflex elicits a single
largely synchronized activation of Ia fibers. The two
elicited reflex responses, therefore, are different and
may affect spinal motoneurons (MNs) in a variety
of ways (i.e., affecting the subliminal fringe in
dissimilar ways), which result in varying efferent
outputs [10-12].
Studies of the H reflex have other methodological
considerations that make interpreting their results a
challenge. For example, when a muscle is activated
electrically compared to more natural forms of
stimulation, the pattern of motor unit recruitment was
shown to be nonselective, spatially fixed, temporally
synchronous, and predisposing the muscle to fatigue
[13, 14]. This recruitment pattern may be responsible
for systematic alterations observed in the maximum
M response (Mmax) when the H reflex is evoked during
a voluntary movement. To compensate these factors,
a strict adherence to experimental techniques is
mandatory [15]. Studying the H reflex, therefore, may
not be the most appropriate way of investigating the
effects of pressure on normal movements in humans
[13]. Differences between the H reflex and SSR may
account for variations in the results following pressure
application.
Finally, investigations looking at the effect of
circumferential pressure (CP) on MNRE have been
mostly conducted on a resting muscle [5, 6, 16]. It is
well known that when an H reflex is superimposed on
a muscle contraction resulting in a limb movement, the
H reflex amplitude increases dramatically before and
during the voluntary contraction of the homologous
muscle [17]. This facilitation has been attributed to
a decrease in the intensity of presynaptic inhibition
at the Ia terminal level rather than by subthreshold
activation of MNs that is seen in the resting muscle
studies. Thus, inhibitory effects of CP on the H reflex,
SSR, and on MNRE in general may be concealed
during voluntary movements [15, 17-20].
In summary, the effect of CP on MNRE remains
uncertain. This is especially true when a combination
of the limb movement and muscle contraction is
considered. Studies using a more natural form of reflex
stimulation superimposed on the limb movement need
to be conducted to understand fully the effect of CP on
MNRE. Therefore, the purposes of our study were: (i)
to determine the CP effect on spinal MNRE using the
more natural SSR experiential technique, and (ii) to
assess CP effects on MNRE during a ramp voluntary
movement.
METHODS
Subjects. Forty-eight subjects with no neurological
deficits volunteered for this study. All subjects read
and signed an informed consent form approved by
the University of Rhode Island Institutional Review
Board. The subjects had no history of neurological
disease or lower limb muscular disorders. All subjects
were asked to refrain from alcohol, caffeine, aspirin,
and heavy exercise 12 h prior to testing [21, 22].
EMG recording. Skin overlying the soleus and vastus
lateralis muscles and over the fibular head were cleaned
and shaven for the EMG electrode placement. Two
9-mm cup silver/silver-chloride EMG electrodes filled
with conductive gel were then placed approximately
3 cm apart on the skin overlying the distal soleus
muscle belly in alignment with the Achilles tendon. A
rectangular metal plate (3-5 cm) was used as the ground
electrode; it was placed on the skin over the fibular
head. A second set of EMG electrodes was placed on
the skin of the anterior lateral thigh, to monitor the
quadriceps activity. This set of electrodes was used
to ensure knee extensors were not compensating for
ankle plantar flexion torque during the experiment.
The EMG electrical activity was amplified (103) at a
bandwidth of 3 to 20 kHz and digitized at a sampling
frequency of 4 · 103 sec–1 using a data acquisition
J. AGOSTINUCCI
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 1 37
analysis system (ADInstruments, USA). Recorded
data were numerically coded, stored, and analyzed by
a computer using the respective data acquisition and
analysis software.
Pressure. Depending on the leg length, a 16-21 cm
pneumatic air-splint was applied around the dominate
calf of each subject. The air-splint was fitted midway
between the head of the fibula and the proximal EMG
recording electrode. A pressure transducer connected
to a bridge amplifier and an oscilloscope monitored
pressure within the air-splint during the experiment.
To decrease the chance of ischemia: (i) the subject’s
blood pressure was taken before the beginning of data
recording. If the diastolic pressure was below 45 mm
Hg, the experiment was terminated; (ii) skin color
distal to the splint was closely monitored during the
pressure phase of the experiment, and (iii) pressure
values were continually monitored and adjusted during
the experiment, to maintain pressures that remained
within a 45-50 mm Hg window.
In addition, it was shown that the methods used in
this study do not cause significant ischemia [23].
Elicitation of the soleus stretch reflex (SSR). These
reflexes were elicited by imposing a 10 deg dorsiflexion
perturbation at a 180 deg/sec velocity, while the
subject plantarflexed against a footplate moving at
90 deg/sec through a 30 deg arc. The perturbation
was initiated at the point when the footplate moved
15 deg. Randomized perturbations were not performed
between and within subjects, because the ankle position
was shown to affect the reflex amplitude [24-26].
The footplate movement was applied using a torque
motor that was under the control of a Galil Motion
Control four-axis servo system (Rocklin, USA) and
a laboratory computer (Dell Inc., USA). The torque
motor/servo system was powerful enough to impose
stereotyped movements irrespectively of changes in
the limb inertia or resisting forces produced by the
subject.
Experimental procedure. This research project
consisted of four phases, a setup/practice phase and
three experimental phases (control phase, pressure
phase, and a second control/postpressure phase). All
the three experimental phases were nearly the same,
with an exception of the pressure application in the
pressure phase. The experimental setup is illustrated
in Fig. 1.
Setup/practice phase (Phase 1). The experiment
began with the subject comfortably seated in a
specially designed chair with his/her dominate knee
bent in 50 deg of flexion and the foot resting on a
footplate in 20 deg of dorsiflexion. The ankle’s axis
of rotation was aligned with the axis of rotation of the
torque motor displacement shaft. The subject’s leg was
then stabilized with straps to the footplate, to prevent
any extraneous movement. A pneumatic air-splint was
then placed around the subject’s calf. The air-splint
was briefly inflated, to allow the subject to become
accustomed to the pressure sensation and provide time
for the air-splint to adjust to the leg dimensions. The
air-splint valve was then opened and allowed to deflate
passively.
At this time, subjects performed three plantar flexion
maximal voluntary contractions (MVCs) against a
stationary footplate, while watching a horizontal line
on a monitor elevating with each contraction. The
monitor provided subjects with visual feedback of their
force production. Maximal voluntary torque (MVT)
was determined from the highest of the three MVCs
and recorded. A twenty-percent MVT (MVT20%) was
then calculated and displayed by a second horizontal
line on the monitor. During the experiment, subjects
were asked to press against the footplate until the
two lines on the monitor were superimposed on each
other. Subjects were allowed to practice until they felt
comfortable with the experimental procedure. Once
proficient, the experiment began. It should be noted
that maintaining MVT20% throughout the movement
arc was not easy, and the subjects had to closely
attend to their performance, to execute this procedure
sufficiently accurately. This arduous task had the
Fig. 1. Scheme of the experimental setup.
Р и с. 1. Схема експерименту.
EFFECT OF CIRCUMFERENTIAL AIR-SPLINT PRESSURE
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 138
added benefit of decreasing the probability of subjects
anticipating the time the dorsiflexion perturbation
occurred during each SSR cycle.
Experimental phases (phases 2-4). Three phases
were conducted in the experimental portion of this
study. In phase 2 (control phase, SSRbaseline), subjects
were asked to plantar flex their foot at MVT20% against
a moving footplate, until the dorsiflexion perturbation
was introduced by the torque motor. Subjects were
not required to resist the perturbation. This procedure
(cycle) was repeated 25 times with randomized
5- to 10-sec-long rest intervals between the cycles. This
was done to decrease the probability of anticipating
the next movement cycle and reflex perturbation. The
SSR EMGs were recorded for each cycle and stored
on a computer for future analysis. Phase 3 (pressure
phase, SSRpressure) began by manually inflating the air-
splint and maintaining it within a 45 to 50 mm Hg
range throughout the phase. With the pressure applied,
the phase 2 procedure was then repeated. The air-
splint was deflated directly after the last recording
was taken. Phase 4 (SSRpostpressure) repeated the phase 2
procedure. Subjects were given approximately 1-min-
long rest period between the phases. Experimental
phases lasted approximately 3-4 min each.
Data acquisition and statistical analysis. For each
subject, 25 EMG samples from each experimental
phase were displayed on a computer screen for SSR
identification (Table 1). The SSR latency and peak-
to-peak amplitude were measured and averaged. The
latency was defined by identifying the first point of
a triphasic waveform from time zero. Time zero was
defined as the first point of the downslope of the
angle change curve (Fig. 2). To ensure the latency
measurement reliability, one experimentally blinded
person performed all latency measurements. The
measurements were conducted twice on two separate
occasions. A paired t-test was conducted on the two
latency measurements, and no statistically difference
was found. Therefore, when a discrepancy between
the two measurements occurred, the shortest latency
was used in the data analysis.
TABLE 1. SSR Inclusion Criteria
1) SSR latency between 35-65 msec
2) Similar SSR configuration throughout experiment
3) No quadriceps activity
4) Able to maintain MVT20% throughout experiment
Peak-to-peak amplitudes were defined by the sums of
the highest and lowest points of the SSR wave (Fig. 2).
Twenty-five SSRs from each recording phase were
then averaged and normalized, by subtracting the
pre-movement mean EMG measurement from the
SSR amplitude mean value [27]. The pre-movement
Fig. 2. Representative trace of the soleus stretch reflex, SSR. A raw averaged record (25 realizations) of the reflex evoked by a 10 deg
dorsiflexion perturbation superimposed on a voluntary ramp plantar flexion. The principle of calculating the SSR latency and amplitude
is graphically shown. The pre-movement mean EMG level was measured within a 50-msec-long window recorded while the subject
volitionally performed contraction before each movement cycle. Lower trace is the record of dorsiflexion perturbation (degrees) in the ankle
joint. The EMG activity was then full-wave rectified, and the average amplitude (500 points) was calculated.
Р и с. 2. Типовий приклад ЕМГ-реєстрації стретч-рефлексу в m. soleus.
mV
0.6
0.4
0.2
0.0
–0.2
–0.4
0
5
10
deg
0 50 100 150 msec
50 msec-long
window
latency
peak-to-peak
amplitude
J. AGOSTINUCCI
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 1 39
EMG value was determined from a 50-msec-long
window recorded during the time the subjects were
volitionally contracting before each movement cycle.
EMG activity was full-wave rectified, and the average
amplitude was calculated. SSR amplitude values
from the before-pressure application were used as the
baseline measurement for each individual subject, and
all other data were compared with the above value.
Each subject, therefore, had his/her own controls.
Friedman Repeated Measures Analysis of Variance
on Ranks tests were used to analyze the pressure
effects for the average latency and average peak-to-
peak amplitude measurements. Parametric testing was
not performed because the data were not normally
distributed and, thus, did not meet parametric testing
criteria. Dunnett’s post-hoc tests were used when the
significance was found (P < 0.05).
To check for experimental consistency, the pre-
perturbation EMG activity (50 msec) and reflex
configurations were closely monitored throughout the
experiment, and any notable change (f > SD) found in
the subject’s data was discarded and not included in
the statistical analysis.
RESULTS
Statistical analysis was performed on the raw data from
43 subjects. The data of 5 subjects were omitted due
to SSR instability or inability to contract consistently
at the MVT20%.
No general significant difference in the SSR
amplitude was found during pressure. Postpressure
values returned to the baseline and were not significant.
Latency measurements also did not differ significantly
from the baseline levels.
Descriptive statistics on the data revealed that the
responses under pressure conditions were variable with
a net mean decrease of 13% (Figs. 3 and 4). The reflex
variability was the likely reason for the nonsignificant
results, with 11 subjects (26%) demonstrating SSR
facilitation, 6 subjects (14%) showing no change, and 26
(60%) subjects demonstrating SSR inhibition (Fig. 4).
A change in the SSR amplitude was defined as having
a > 10% change from the baseline values [16].
DISCUSSION
Our study showed that circumferential pressure
applied by an air-splint around the lower leg does
not significantly reduce the soleus stretch reflex
during voluntary plantar flexion in subjects without
neurological disorders. These findings contradict
the results of previous soleus H reflex studies
where significant reflex inhibition was reported in
all subjects tested. The insignificant global change
in SSR amplitude was most probably due to great
interindividual variability (Fig. 4): 40% of the subjects
responded with either reflex facilitation (26%) or no
change at all (14%). This variability in the reflex
amplitude has not been reported in other soleus H
reflex studies [5, 6].
It is an arduous task to decide, which mechanism is
primarily responsible for the reflex variability observed
in our study. The application of continuous pressure
around a limb activates a wide spectrum of afferents
and spinal circuits. This is further complicated by
superimposing an SSR onto a voluntary contraction.
Burke et al. [28] showed that the fusimotor system
is co-activated with the skeletal motor system when
a voluntary contraction (movement) is initiated. This
increase in fusimotor drive is especially evident when
movements are conducted slowly against an external
load.
The role of the fusimotor system is to increase the
gain of muscle spindles when voluntary movements
Fig. 3. Normalized mean changes and their standard deviations (%)
for the SSR amplitude measured in all 43 subjects under conditions
of application of circumferential pressure and within the post-
pressure period (1 and 2, respectively).
Р и с. 3. Нормовані значення середніх та стандартних відхилень
(%) амплітуди стретч-рефлекса, зареєстрованих у групі із 43
тестованих в умовах прикладання кругового тиску та після його
зняття (1 та 2 відповідно).
100
50
0
–50
–100
Baseline
1 2
%
EFFECT OF CIRCUMFERENTIAL AIR-SPLINT PRESSURE
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 140
are initiated. The resulting increase in Ia activity
accompanying muscle contraction is postulated to
provide an overall excitatory effect on the MN pool
rendering support to the muscle contraction [29].
Contractions requiring greater effort levels would
presumably enhance fusimotor drive, while less effort
would result in diminished fusimotor activity. In this
study, subjects were required to plantar flex their foot
through a 30 deg arc, while pressing against a footplate
with MVT20% at a velocity of 90 deg/sec. Thus, the
variable SSR responses observed in this study may be
a direct result of the effort level maintaining MVT20%
by the subject superimposed onto general inhibition
caused by CP. Subjects requiring greater efforts would
have an enhanced reflex arc activity, while a less effort
corresponds to a more inhibited reflex arc. Conversely,
when a muscle is completely relaxed, as in standard
H reflex studies, the fusimotor activity is insufficient
to maintain a significant spindle discharge (unloaded
muscle spindles) [28]. The Ia afferent activity in
response to a random stretch would be lower and more
stereotypic. All results of the studies investigating the
effect of ramp movements on the H reflex support this
hypothesis [28, 30].
The feasibility of this hypothesis depends on the
ability of muscle spindles to communicate with spinal
MNs during the muscle contraction without their
activity being inhibited by presynaptic inhibitory
interneurons. Hultborn et al. [31] showed that, just
before a voluntary movement onset, the excitability
of interneurons mediating presynaptic inhibition is
decreased by higher centers allowing afferent activity
to be transmitted to the MN pool. This concomitant
mechanism of activation of the spindles simultaneously
with decreasing presynaptic inhibition of Ia terminals
will undoubtedly result in varying afferent activity,
depending on the relative exertion each subject
requires to accomplish the movement.
Another possible spinal mechanism that may
account for the SSR variability is the simultaneous
decrease in non-reciprocal inhibition (autogenic
inhibition) that occurs when a limb contracts against
a resistance. Agostinucci et al. [16] suggested Golgi
tendon organs (GTOs) may be partly responsible
for the H reflex variability in the flexor carpi
radialis when CP was applied around the forearm.
They argued stating that GTOs were not just simple
predictable pathways with a single function but
have rather variable effects depending on the task
performed, the muscle activated, and the inputs from
other neuronal systems [32-35]. It is quite plausible
that the effect of CP on MNRE may change when
a reflex is elicited in a contracting muscle. Faist
et al. [36] supported this conclusion. They showed
that Ib inhibition onto MNs is present only during
non-loaded situations; when a limb is loaded, Ib
inhibition is reduced. With less inhibition projecting
onto MNs, the SSR amplitudes would presumably be
higher and more variable, again depending on the
subject’s relative exertion.
Methodological considerations. It has been
suggested that the SSR may be a more appropriate
technique than the an “electrical” equivalent (H
reflex) to assess MNRE because it uses a more natural
Fig. 4. Soleus stretch reflex peak-to-peak
amplitude data grouped according to the effects of
circumferential pressure on this parameter. Subjects
were grouped by having a >10% facilitation of the
SSR, negligible changes, and >10% inhibition of
the reflex. Means, standard deviations, and number
of subjects n are shown. 1 and 2 are the same as in
Fig. 3.
Р и с. 4. Значення амплітуди стретч-рефлексу
в m. soleus, згруповані відповідно типу впливу
кругового тиску на цей параметр.
1
2
1 1
2
2
100
50
0
–50
–100
Baseline
n = 11 n = 6
n = 26
Facilitation < 10% change Inhibition
%
J. AGOSTINUCCI
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 1 41
stimulus to elicit the reflex. This argument is based on
the well-know fact that the H reflex bypasses muscle
spindles and, therefore, does not take into account
their influence [7, 8, 10]. Results of our study show
that circumferential pressure does not inhibit the SSR
to the same extent as the H reflex demonstrated. In
fact, H reflex inhibition exceeds the SSR suppression
even when the subjects with SSR facilitation are
not included in the analysis [5]. It was suggested
above that fusimotor drive and the resulting change
in Ia facilitatory input onto MNs during voluntary
contractions were partially responsible for the SSR
variability observed in this study. The SSR may
simply represent the effect that CP has on MNRE when
the influence of muscle spindles has been included.
Since the fusimotor/muscle spindle system plays an
important modulatory role affecting MN excitability
[29], the SSR may be a more appropriate technique
to use in assessing MNRE. This is especially evident
when voluntary movements are conducted. This view
is supported by studies by Morita et al. [37] and Baudry
et al. [38] who showed that the SSR and the H reflex
have different sensitivities to presynaptic inhibition.
Further studies are needed to determine the effects of
CP on MNRE during voluntary movements. It seems
quite possible that the role of CP in influencing the
reflex excitability of motoneurons is more limited than
that previously thought, especially when evaluating its
effects on the voluntary movements in people with no
neuromuscular disorders.
Postpressure phase. The SSR amplitude did not
differ significantly from the baseline levels (Figs. 3
and 4). However, the mean normalized change in the
SSR amplitude was facilitatory; this index exceeded
the pressure trial values whether the subjects responded
to pressure with facilitation or not (Fig. 4). This
increase in the SSR amplitude above pressure levels
is likely due to a cooling effect of ambient air entering
underneath the splint when the splint loosens around
the leg. Skin cooling was shown to facilitate both the
H reflex and the SSR [39-41].
In conclusion, the results of our study clearly show
that CP effects may noticeably differ from each other
when movements are a condition. This view is in
agreement with several critical reviews where task-
oriented interventions induced a more substantial
functional improvement in people post CVA [42,
43]. Although these results cannot determine the
mechanism specifically involved, they do bring into
question the usefulness of conducting treatments on
resting muscles. In addition, when assessing MNRE
during voluntary movement, the SSR may have a
conceptual advantage over the H reflex.
Clinical implications. CP studies on the soleus
have shown that reflex excitability of motoneurons
decreases in all subjects and patients tested [5, 6].
These authors supported the use of circumferential
pressure as a therapeutic modality when treating the
lower limb muscle activity. Our results, however, are
not as conclusive because they showed circumferential
pressure does not affect everyone in the same way
when muscle contraction and movements were a
condition. A therapist must be cognizant of these
contrasting affects and only use circumferential
pressure in appropriate individuals. This is especially
true after pressure release, where a temporary increase
in MNRE was observed in ~70% of the subjects.
Clinicians, therefore, should routinely monitor their
treatment effects to assure if functional outcomes in
their patients are what was expected, since individual
responses may vary significantly.
Дж. Агостінуччі1
ВПЛИВ ПРИКЛАДАННЯ КРУГОВОГО ТИСКУ
(ЗА ДОПОМОГОЮ ПНЕВМАТИЧНОЇ МАНЖЕТИ) НА
СТРЕТЧ-РЕФЛЕКС У КАМБАЛОПОДІБНОМУ М’ЯЗІ,
ЗАРЕЄСТРОВАНИЙ НА ТЛІ ДОВІЛЬНОЇ ПЛАНТАРНОЇ
ФЛЕКСІЇ
1 Університет Род Aйленда, Кінгстон (США).
Р е з ю м е
Було показано, що круговий тиск (КТ), прикладений до кін-
цівки, зумовлює зменшення м’язової активності в осіб без
нервово-м’язових розладів і у пацієнтів з пошкодженнями
спинного мозку й цереброваскулярними патологіями. До-
нині в дослідженнях, спрямованих на оцінку ефективнос-
ті КТ щодо рефлекторної збудливості нейронів, переваж-
но використовувалася методика відведення Н-рефлексу від
м’яза в стані спокою. У даній роботі вивчалися впливи КТ
на стретч-рефлекс (СР) у m. soleus, котрий був зареєстрова-
ний на тлі довільної трапецієподібної плантарної флексії в
осіб без нервово-м’язових розладів. У тестах брали участь
48 добровольців. СР реєстрували перед прикладанням тис-
ку до литки ноги протягом і після такого прикладання. Для
прикладання й виміру тиску використовували пневматич-
ну манжету з’єднану з датчиком. СР викликали дорсифле-
кією ступні на 10 град зі швидкістю 180 град/с, тоді як тес-
тована особа здійснювала плантарну флексію з упором на
рухому педаль із зусиллям 20 % максимального довільного
скорочення в межах дуги 30 град при швидкості 90 град/с.
У межах кожної експериментальної фази реєстрували й усе-
реднювали 25 реалізацій СР. Вимірювалися амплітуди СР
EFFECT OF CIRCUMFERENTIAL AIR-SPLINT PRESSURE
НЕЙРОФИЗИОЛОГИЯ / NEUROPHYSIOLOGY.—2010.—T. 42, № 142
(від піка до піка); їх величини нормувалися. Вимірювали-
ся також величини латентного періоду (ЛП) досліджува-
ного рефлексу. Відмінності величин ЛП й амплітуд СР від
вихідних значень оцінювалися з використанням аналізу по-
вторних змін рангових варіацій Фрідмана. Істотних загаль-
них відмінностей амплітуди СР, пов’язаних з прикладанням
тиску, не було виявлено, хоча індивідуальні величини від-
повідей варіювали в широких межах. Амплітуди в інтервалі
після прикладання тиску поверталися до вихідних, і їх від-
мінності не були істотними. ЛП рефлексу також не зміню-
валися порівняно з вихідними значеннями. Отже, знижен-
ня рефлекторної збудливості мотонейронов під впливом КТ
було в середньому незначним і демонструвало істотну ва-
ріабельність у тих випадках, коли ефект цього впливу реє-
струвався на тлі довільного руху. Методика КТ, видимо, не
є настільки ефективною в аспекті зниження м’язової гіпе-
рактивності, як це вважалося раніше.
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