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Russian Journal of Biomechanics
REGULARITIES OF A CHANGE OF ELECTROMYOGRAPHIC PATTERN OF MUSCLES IN NORMAL AND PHYSICALLY MODELED HUMAN
WALKING
Federal scientific and practical center of expertise and rehabilitation of invalids, 3, Ivan Susanin street, 127486, Moscow, Russia, e-mail: [email protected]
Abstract. Electromyographic and biomechanical investigations of different types of normal and physically modeled walking allowed to establish, that regular and irregular waves of the electrical activity of muscles may be examined during the locomotor cycle. Authors suggested to mark out three zones in EMG-pattern during walking: zone M (the maximal activity) and zone T (the moderate activity) belong to a period of the centrally programmed excitation, and zone L (the low-amplitude activity) - to a period of the centrally programmed inhibition. Difference between the first two zones consists in the fact, that activity in zone M is regular, while activity in zone T is irregular and ranges depending on biomechanical conditions. A new hypothesis has been put forward, that regular and irregular waves of activity during walking have different origin and possible, the afferent influences play role in its genesis. The examples of changes of regular and irregular waves of activity in different types of walking are adduced in this article.
Key words: EMG-pattern of muscles, zones of muscle activity during walking, normal walking
To our days there is no general conception of a change of electromyographic pattern of muscles during both normal and pathological walking. Most of authors restrict their description to regular waves of the electrical activity and their biomechanical effect in the locomotor cycle [1-13].
At the same time the regular waves of the electrical activity change in amplitude, duration and phase in some situations; besides, the separate waves of the electrical activity, not typical under walking at the optimal cadence, may appear or disappear. Strictly speaking, the latter waves cannot be considered as the correctional ones, as differentiated from the regular force waves [4], because they appear under quite definite conditions, that change kinematics and dynamics of walking.
In this investigation the authors have made an attempt to elaborate the general conception of a change of EMG-pattern of muscles during human walking on the basis of synthesis of neurophysiological and biomechanical data, received in studies of locomotion.
Methods
Electromyographic and biomechanical investigations of different types of normal and physically modeled walking, carried out previously, were the subject of analysis.
A.S. Vitenson, K.A. Petrushanskaya
Introduction
Synchronous registration of the electrical activity of muscles and kinematic and dynamic parameters of walking. was applied in all experiments. The electrical activity of muscles was registered by means of bipolar surface electrodes in the form of the metal cups of 1 cm in diameter, the distance between electrodes was 40 cm. The electrodes were filled with the electrode paste and placed on a rubber base. Then activity was strengthened by UBF-4 biopotentials amplifier and registered through Analog-to-Digital Converter to Personal Computer in the form of linear envelope with the time constant of 10 ms. The measured parameters (podogram, angular displacements, and linear envelope of EMG) were processed at a frequency of 200 times/s, after that the average activity (in mkV) for every 5% of a cycle was calculated, and graphs of changes of kinematic and electrophysiological indices for the locomotor cycle were drawn.
In more early investigations the parameters of walking were registered by the lightradial oscillograph, and EMG was registered in natural and integrated form.
Results of investigations. Central innervative program of walking
Numerous electrophysiological investigations of walking showed the remarkable monotony of EMG-pattern of muscles in different groups of examinees. The individual differences of electromyograms are confined only to some distinctions of the amplitude values of activity. As far to distribution of activity for the locomotor cycle, it remains practically the same. Such constancy of the innervative structure of walking particularly catches the eye while considering EMG-pattern of muscles of the lower extremities at different velocity (or walking cadences). Figures 1-2 illustrate EMG-pattern of muscles - m. tibialis anterior, m. gastrocnemius, m. vastus lateralis and m.semitendinosus in a wide range of cadences (from 68 to 138 steps/min). One can see high recurrence of the curves. The main changes come to increase of an amplitude of waves of activity and to a slight shift of the maximal values to the beginning of a cycle.
Figure 1. Change of the electrical activity of the shank muscles (a - m. gastrocnemius, b - tibialis anterior) during the locomotor cycle at different walking cadences. S1 - the slowest cadence, S - slow cadence, N - natural cadence, F - fast cadence, F1- the fastest cadence.
Figure 2. Change of the electrical activity of the thigh muscles (a - m.vastus lateralis, b - m.semitendinosus) during the locomotor cycle at different walking cadences. Note: all signs are the same as in Fig. 1.
Such inconsiderable change of muscle work while increasing walking velocity shows the justice of Bernshteins statement [14] that "walking belongs to the highly automated movements, characterized by generality, extraordinary stable and typical structure".
At the same time, according to N.A. Bernshtein [15], work of muscles comprises only one "share" in structure of movements, other components form the external, inertial and reactive forces. Change of the latter ones determines instability of a biomechanical situation, and consequently, demands persistent correction of the muscle forces.
So, a dialectic contradiction appears between the necessity of preservation of the rational innervative gait structure and its variability, connected with a change of environmental conditions. .
Successful solving this contradiction may be achieved by the expedient transformation of EMG-pattern of muscles, as a result of which, on the one hand, the basic elements of the structure are retained, and on the other hand, the separate waves of activity appear or, on the contrary, disappear.
For the purpose to realize the internal mechanism of this phenomena, let us call our attention to the modern ideas of the system of control of locomotion, received in experiments on animals [16-20] and in electrophysiological investigations of human walking [4, 9].
The simplified scheme of the structure of control of muscle work during locomotion is presented in Fig. 3. One can see, that program of the step movements is formed already at the spinal cord level. Different regions of the brain are responsible for such functions as the start of this program, control of its intensity, organization of the interlimbed interaction, maintance of balance and others. The afferent inflow from the extremities is the necessary component of this system. This inflow serves both for the activation of the intraspinal mechanism and for realization of different corrections at the level of the spinal cord and brain.
The central innervative program also functions in human walking. One can judge this program according to distribution of the electrical activity of muscles during the locomotor cycle.
In spite of the multilevelled character of control, the activity of the relatively autonomous spinal generator of locomotor movements underlies this program.
Figure 3. Structure of control of muscle work in locomotion of animals. 1 - cerebral cortex, 2 - hypothalamic locomotor region, 3 - mesencephalic locomotor region, 4 - reticulo-spinal neurons with slow-conductive fibres and monoaminoergic neurons, 5 - automatic system for the interlimbed interaction and balance ( lower part of the brain stem and cerebellum), 6 - spinal mechanism of stepping (generator of locomotor movements), 7 - nonproducer interneurons, 8 - motoneurons, 9 - muscular fibres (extrafusal), 10 - muscle
receprors, 11 - other receptors of the extremity.
Later on for neurophysiological analysis we shall hold to Brown's hypotheses [21], subsequently developed by Jankowska [22], and also by Feldman, Orlovsky [23], Baev [19] and others.
According to this hypothesis, mostly substantiated by the experimental investigations, the generation of locomotor movements is considered as a result of inhibitory interaction of hemicenters of muscles-antagonists. This hypothesis satisfactory explains a number of facts:
1) the main distribution of muscle activity during phases of a step (including alteration of periods of excitation and inhibition in work of the locomotor centers);
2) reciprocal organization of the afferent and descending (supraspinal) influences on these centers;
3) rhythmical activation of interneurons and motoneurons of muscles-extensors and flexors after introduction of DOPA to the spinal cats;
4) simultaneous fluctuation of the level of activation of the different motoneuron pools during fictitious locomotion of the decerebrated cats, what supposes close connection of motoneurons with one of the hemicenters of the locomotor generator.
The special investigations count in favour of this theory. These investigations have revealed the morphological substrate of this generator with great probability. This substrate is situated in the lateral parts of the intermediate zone of the grey matter and the ventral horn at the level of L3-L7. It has been established, that there are interneurons in this zone, possible
1000 mkV
50 imp/s = 50 mkV
0,5 s
Figure 4. Change of gait parameters in phase switch-off of movements at the KJ: a - natural walking, b - stop of movements at the KJ in the middle of the swing phase, c - stop of movements at the KJ at the end of the stance phase of a step. RP - right podogram; m quadr. and m. semit. - integrated and natural EMG of m. quadriceps femoris and m. semitendinosus. KJ - the knee joint. M - mark of the switch-off of movement at the KJ.
identical with the flexor and extensor hemicenters (F and E). These interneurons pulsed during locomotion correspondingly in swing and stance phases. Besides, the mixed interneurons - FE have been also disclosed. These interneurons became active in both phases of work of a locomotor generator [24, 25, 26].
Our investigations [9] have established the existence of the central innervative program of muscles-antagonists in human walking. This program consists of phases of excitation and inhibition. Work of muscles-extensors is strictly timed to the stance phase, what supposes their activation from the extension hemicenter of the locomotor generator.
Figure 4 a, b demonstrates an experiment, promoting to revealing the intraspinal program in human walking: the experiment consists in introducing the transitory excitation into the biomechanical structure of walking for the time of 50-500 ms with the help of the orthopaedic device with the electromagnetic brake and the simultaneous registration of the
angle of ~ 60° (r)
responsive changes of the kinematic and dynamic parameters. These investigations were carried out repeatedly on 5 examinees. Phase and duration of a movement's stop were changed regularly with the purpose to exclude a possibility of formation of the conditional senso-motor reflex.
Stop of a movement was carried out at the greatest angle of flexion at the knee joint in the swing phase, in the process the electrical activity of m. quadriceps femoris and m. semitendinosus in natural and integrated form was registered. It was established, that if locking of the joint lasted no longer than 100 ms and had time to finish before the beginning of excitation of m. quadriceps femoris, reaction did not take place at all or it was revealed in extremely reduced form. And only in those cases, when this locking achieved the excitation phase, reaction appeared in a form of high-amplitude and long burst of activity (Fig. 5).
Figure 5. Change of gait parametrs in varying of duration of locking of the KJ: a) natural walking, b) locking of the joint for a time more than 100 ms, c) locking of the joint for a time less than 100 ms, d) locking of the joint at the end of the swing phase. RP - right podogram, LP - left podogram; m. quadr., m.semit., m.rect. fem. and m. bic. fem. - integrated and natural activity of m. quadriceps femoris, m.semitendinosus, m. rectus femoris and m. biceps femoris. KJ and HJ - the knee and hip joints. An arrow points to the beginning of locking of the joint.
Stop of a movement at the knee joint at the end of the stance phase, preventing from flexion at the knee joint, causes the premature appearance of activity of m.semitendinosus with a short latent period (Fig. 4c).
At last, stop of a movement at the knee joint at a peak of flexion may change the beginning, duration and degree of muscle activation. As may be seen from Fig. 6, the main wave of the electrical activity of m. gastrocnemius may transfer from the middle third of the stance phase to its beginning or even bifurcate, during which wave of activity appears at the beginning, and the second one - in the middle third of the stance phase.
These and many other investigations allowed to establish not only the existence of the intraspinal program in human walking, but also to reveal peculiarities of this program for muscles-antagonists.
It has been ascertained, that a more rigid program is inherent for muscles with a force function, i.e. - for muscles-extensors. The most characteristic features of this program are: clear delimitation of phases of activity and rest, the primary concentration of excitation in the stance phase of a step, weak reactivity at the period of bioelectric silence, insignificant variability of different electrophysiological parameters under changes of walking conditions,
1000 mkV
50 imp/s = 50 mkV 0,5 s
Figure 6. Change of gait parameters in a sudden locking of the KJ in the extension phase: a) natural walking, b, c - walking with locking of the KJ in the extension phase. RP - right podogram, LP - left podogram, m. quadr. and m. gastr. - integrated and natural EMG of m. quadriceps femoris and m. gastrocnemius. AJ - the
ankle joint, KJ - the knee joint.
angle of fin0
more early formation of this program in a process of ontogenesis. More adaptive program is peculiar to muscles-flexors [9, 11].
Difference of the innervative programs of muscles-antagonists should be explained by morpho-fucnctional structure of a locomotor generator and also by peculiarities of its afferent and supraspinal connections.
All of the received literary and own data give an opportunity to postulate, that it is necessary to distinguish the centrally programmed periods of excitation and inhibition in the electrical activity of every muscle.
Zones of activity of muscles during the locomotor cycle and hypotheses of their genesis
We suggest that three zones should be distinguished in EMG-pattern of muscles during walking: from which zone M (the maximal activity) and zone T (the temperate activity) belong to a period of the programmed excitation, and zone L (low-amplitude activity) - to a period of the programmed inhibition.
Distinction between the first two zones lies in the fact that activity in zone M is regular, while activity in zone T is irregular and ranges in accordance with the biomechanical conditions of walking.
Figure 7. Zones of the electrical activity of muscles during the locomotor cycle: M -maximal activity, T - temperate activity, L - low-amplitude activity.
Zones of activity for different muscles of the lower extremities are presented in Fig. 7.
As evidently from this Figure, zone of M-activity of m. gastrocnemius is placed at the interval 25%<t<55% of the cycle, zone T begins at t = 90% of previous cycle and ends at t = 25% of the next cycle, zone L is situated in the interval 55%<t<90% of the cycle.
M-activity of m. vastus lateralis arises at t = 90% of the previous cycle and finishes at t = 25% of the next step, zone T is placed in the interval 25%<t<55% of the cycle and zone L is located in the interval 55%<t<90% of the cycle.
Consequently, the period of excitation for muscles-extensors in a cycle (zones M + T) occupies the interval from the end of the swing phase till approximately the first two thirds of the stance phase.
Borders of zones of activity of muscles-flexors (m. tibialis anterior and m.semitendinosus) are approximately the same. The beginning of M-zone is timed to the end of the swing phase (about t = 85% of the cycle) and its end - to t=25% of the next cycle; zone T proceeds to zone M in the interval 55%<t<85%, and zone L is situated in the interval 25%<t<55%.
It may seem for the sight, that the level of activity in zones T and L is about the same, but this phenomenon is observed only at the optimal walking cadence: in all perturbations of biomechanical character the activity in zone T may considerably increase.
As it was mentioned, zones of activity in the locomotor cycle reflect different functional states of the neuronal apparatus of the spinal cord, and first of all - of the motoneuron pool.
This fact is confirmed by neurophysiological investigations, specifically - H-reflex during walking. Study of H-reflex of m. soleus showed, that the value of the reflex reaction changes in parallel with the level of the electrical activity for the locomotor cycle [27, 28, 29].
What is the reason of different regularity of waves of the electrical activity in zones M
and T?
At present it is possible to set up only some hypotheses on the basis of literary and our own observations.
Probably, it is necessary to distinguish systems, determining program of phases of excitation and inhibition in the motoneuron pool and systems, providing change of a pattern of excitation during the programmed phase.
Spinal generator, realizing postsynaptic excitation and inhibition of motoneurons through the interneurons Ia, and also the mechanism of presynaptic inhibition (probably conditioned by the same generator), belong to the first systems [30, 19], they form so-called primary factor.
This stage of program is reinforced by the cyclic influences, realizing through the cerebellar loop and namely - through the ventral spinocerebellar tract (Govers' tract), cerebellum, truncated nuclear and descending ways (vestibulo-spinal - for muscles-extensors, rubro- and reticulo-spinal - for muscles-flexors). This is probably the secondary factor, which is also a reflection of the spinal processes, and specifically - the activity of the spinal generator of locomotion [20].
Afferentation from the different receptors of the extremity should be assigned to the secondary systems. This afferentation may influence on activity of the spinal locomotor generator, and also - on interneurons and motoneurons of the reflex arc [16].
As this takes place, it necessary to mark, that afferents of the flexor reflex (high-treshold cutaneous and muscular, vascular) promote to work of a locomotor generator, while the muscular afferents Ia and Ib are deposited on the intraspinal program of locomotion and
*
with the help of the proprioceptive reflexes change the pattern of excitation of muscles . These reflexes fulfill the triple function: they strengthen, weaken and transfer activity in the limits of the programmed phase of excitation.
Probably, activity in zone M in usual conditions is less susceptible to the inhibitory afferent influences than activity in zone T because of the phase reinforcement of excitation from the side of the descending supraspinal systems (vestibulo-, rubro- and reticulo-spinal) and a number of excitatory afferent influences.
The considered ideas of the genesis of regular and irregular waves of activity may be illustrated by a number of examples, received in studies of normal and physically modeled walking.
Level and stairs walking
Figure 8 shows that during upstairs walking the activity of m. vastus lateralis and m. gluteus maximus is prolonged to zone T, while during level walking the activity is limited by zone M; during downstairs walking the activity of m. vastus lateralis occupies also two zones: (M and T), and the activity of m. gastrocnemius disappears in zone M and completely transfers to zone T.
As may be seen from Fig. 9, during upstairs and downstairs walking the activity in zone T sharply increases in a number of muscles: in tibialis anterior, m. semitendinosus and m. biceps femoris. In all cases, considered above, prolongation of activity to zone T is biomechanically expedient. This prolongation provides lifting of a human body on the next
Figure 8. EMG-pattern of muscles-extensors in norm during level walking (A), during upstairs (B) and downstairs (C) walking. Note: all signs are the same as in Fig. 7.
* According to data of a number of neurophysiological investigations, afferents I b of muscle-extensors excite the extensor hemicenter of the locomotor generator during the extensor phase of walking [31, 32]. Low-threshhlod cutaneous foot afferents influence in the same way [33, 34].
mkV 17i. tibialis anterior mkV m. semitendinosus mkV m. biceps
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Figure 9. EMG-pattern of muscles-flexors in norm during level walking (A), during walking upstairs (B) and downstairs (C) walking. Note: all signs are the same as in Fig. 7.
footstep for muscles-extensors and more effective displacement of the lower extremity in the swing phase - for muscles-flexors.
Changes of EMG-pattern may be explained from the neurophysiological point of
view.
Prolongation of the activity of knee- and hip-extensors to zone T in conditions of positive work should be considered as a mechanism of compensation of loadings (during upstairs walking extension at both of the joints occurs with overcoming of the body's mass). Since in this case muscles, extended earlier, are shortened the reflex maintenance of the alpha-motoneuron pool from the side of the muscle spindles becomes necessary. Obviously, here we are dealing primarily with the static responses of the muscle spindles, regulated by the statical gamma-motoneurons. Positive responses of other afferents, for example I b and low-threshold ^taneous ones must not be ruled out.
Another situation takes place during downstairs walking. In this case the two-peaked EMG-pattern of the mentioned muscles-extensors appears. This pattern coincides in time with minimum of the vertical component of a ground reaction force (Rz). Consequently, it is conceivable, that decrease of loading on muscles in the middle of the stance phase leads to the certain reduction of muscle activity and it is a reason of appearance of two-humped curve (Vitenson A.S.). It is necessary to underline, that the second maximum arises in zone T.
Appearance of a wave of activity of m. gastrocnemius in zone T during downstairs walking may be assigned to the similar category of effects (in this case muscle functions in the regime of negative work, preventing from the rapid dorsal flexion at the ankle joint and creating the certain supportability of the lower extremity). In this variant rather quick lengthening of a muscle occurs, and this lengthening must be accompanied by strengthening of the static and dynamic responses of the muscle spindles.
Changes of EMG-pattern of muscles-flexors are more original. During upstairs walking upstairs activity of these muscles remarkably increases in the swing phase of a step. In the process, an unusual wave of activity of m. semitendinosus and m. biceps femoris appears in zone T. In usual conditions this wave is marked only at very slow cadence, and
besides, under insufficiency of function of m. gastrocnemius. The absence of this wave of activity at the optimal walking cadence is conditioned by the fact that flexion at the knee joint in the swing phase takes place as a result of a push, produced by flexion of m. gastrocnemius. This situation determines shortening of knee flexors, unloading of muscle spindles and reduction of the reflex activity.
So, investigations of stairs walking confirm a hypothesis of appearance of irregular waves of activity in zone T under the influence of the certain biomechanical conditions, which change the character of afferentation from the muscle receptors of the lower extremity.
In this conditions one more fact engages our attention - dissimilar phase duration and intensity of periods of inhibition during the cycle in different locomotor acts. So, period of inhibition of m. gastrocnemius during level walking lasts from 55% till 90% of a cycle, during upstairs walking - from 65% till 90% of a cycle and during downstairs walking- from 55% till 90% of a cycle. The analogous phenomena are marked in EMG-pattern of the other muscles.
This observation confirms the fact, discovered earlier, that the intermediate zones exist between the periods of excitation and inhibition. If the force of afferentation is sufficient, then excitation may appear in such intermediate zone [11].
Figure 10. EMG-pattern of muscles during walking in norm and with different step length. Dotted line: step length - 0.35 m, solid line - 0.75 m, spotted line - 1.15 m.
Walking with different step length
The similar phenomenon of appearance of irregular waves of the activity in zone T may be observed also during walking with different step length [35]. Investigations showed, that EMG-pattern, peculiar to normal walking, usually remains during walking with step length in the range from 0.35 m to 0.75 m and cadence about 100 steps/min. But if the step length considerably rises (0.95-1.15 m), then in parallel with growth of the electrical activity of m. gastrocnemius in zone M, a high wave of the activity of other extensors (m. vastus lateralis, m. rectus femoris and m. gluteus maximus) appears in zone T almost synchronously (Fig. 10). This wave proceeds to a sharp plantar flexion at the ankle joint (Fig. 11) and to increase of push-off [11]. Probably, momentary fixation of the main joints of the extremity in phase of push-off increases efficiency of push of the extremity from the support.
Physical modelling of some disorders of walking
Afferent factors may influence not only on activity, localized in zone T. In certain conditions, which considerably disturb the character of movements, these changes spread to the regular waves of activity in zone M.
A change of EMG-pattern of m. triceps surae in immobilization of the ankle joint with the help of the special orthopaedic device is the example of such transformation. In this case activity of uniarticular m. soleus considerably reduces in zone M, while its activity in zone T remains approximately the same.
Ankle angle
Figure 11. Kinematic parameters during walking in norma and with different step length. Dotted line: step length 0.35 m, solid line - 0.75 m, spotted line - 1.15m.
o 20 40 60 80 100
0 20 40 60 80 100
Figure 12. EMG-pattern of m.soleus during the locomotor cycle in norm and in orthopaedic device on the ankle joint. Thin line - immobilization of the joint at the angle of 90°, thick line - natural walking.
This effect is clearly pronounced at different walking cadences (Fig. 12). The immobilization influences on the activity of biarticular m. gastrocnemius to a lesser degree (Fig. 13). Decrease of the activity is observed only in zone M at slow and natural walking cadences: at fast cadence EMG- pattern of m. gastrocnemius is completely restored [36].
The received data give an idea of the role of the afferent factors in human walking. Considerable reduction of precisely that head of m. triceps surae, which ceases to extend and undergo loading in conditions of immobilization of the ankle joint, probably, shows the existence of the reflex mechanism of activation of alpha-motoneurons. In this case the exception of mobility at the joint can be likened with some simplification to a blockade of gamma-acsons to the muscle spindles of the same muscle [37].
The above-mentioned similarity is derived from the fact that excitation of alpha-motoneurons through gamma-loop is possible only under the certain value of the afferent inflow from the muscle spindles.
The value of this inflow is determined, on the one hand, by the initial value of pulsation from the muscle spindles, and on the other hand, by strengthening of this pulsation by means of gamma-activation [38, 39]. If the initial pulsation from the muscle spindles is not great because of immobilization of the joint, the afferent inflow even after gamma-activation would not progress to the value which is necessary for excitation of alpha-motoneurons. As regards to restoration of activity of m. gastrocnemius, especially at fast cadence, it takes place
Figure 13. EMG-pattern of m. gastrocnemius during the locomotor cycle in norm and in ortopaedic device at the ankle joint. Note: all signs are the same as in Fig. 12.
at the expense of the retained afferent inflow, which appears during movements at the knee joint. This inflow is strengthened by gamma-activation, determined by increase of walking velocity.
As it can be seen, proprioceptive afferentation from the extremity essentially changes EMG-pattern of muscles under disorder of biomechanical structure of the locomotor act.
Conclusions
1. The central innervative program exists during walking. This program is formed with participation of many regions of the brain and spinal cord. But the activity of the intraspinal mechanism of the step movements forms the basis of this program. This mechanism sets up the cyclic sequence of muscle work.
2. It is necessary to distinguish periods, corresponding to excitation and inhibition of the motoneuron pool in the innervative program of every muscle. Under these conditions it is possible to mark out two zones in the period of excitation - M and T, characterizing the regular wave of the electrical activity and irregular wave of the temperate activity.
3. The stability of the maximal waves of activity (zone M) is probably determined by the total action of the spinal generator of the locomotor movements, cyclic supraspinal
influences and different, first of all proprioceptive afferentation from the extremity. Strengthening of the activity in zone T predominantly depends on the afferent influences.
4. During walking afferent factors may change the beginning, duration and degree of muscle activation, and may also essentially change the pattern of the electrical activity, removing its maximum from one phase to another one. But these changes are possible only in the limits of the programmed period of excitation, at least for uniarticular muscles.
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ЗАКОНОМЕРНОСТИ ИЗМЕНЕНИЯ ЭЛЕКТРОМИОГРАФИЧЕСКОГО ПРОФИЛЯ МЫШЦ ПРИ НОРМАЛЬНОЙ И ФИЗИЧЕСКИ МОДЕЛИРОВАННОЙ ХОДЬБЕ ЧЕЛОВЕКА
А.С. Витензон, К.А. Петрушанская (Москва, Россия)
Посредством электромиографических и биомеханических исследований различных видов нормальной и физически моделированной ходьбы установлено, что в течение локомоторного цикла наблюдаются регулярные и нерегулярные волны электрической активности мышц.
Авторами предложено в электромиографическом профиле мышц при ходьбе выделять три зоны, из которых зона М (максимальная активность) и зона У (умеренная активность) относятся к периоду центрально запрограммированного возбуждения мотонейронного пула, а зона Н (низкоамплитудная активность) - к периоду центрально
запрограммированного торможения. Различие первых двух зон заключается в том, что в зоне М активность является регулярной, тогда как в зоне У активность нерегулярна и колеблется в зависимости от биомеханических условий.
Устойчивость максимальных волн активности (зона М) определяется, по-видимому, совокупным действием спинального генератора локомоторных движений, циклических супраспинальных влияний и различной, прежде всего проприорецептивной афферентацией от конечности. Усиление активности в зоне У преимущественно зависит от афферентных воздействий.
Афферентные факторы при ходьбе могут изменять начало, длительность и степень активации мышц, а также существенно трансформировать и самый рисунок их электрической активности, смещая её максимум из одной фазы шага в другую. Однако такие изменения возможны лишь в пределах запрограммированного периода возбуждения, по крайней мере для односуставных мышц.
Ключевые слова: электромиография, профиль мышц, зоны электрической активности мышц при ходьбе, нормальная ходьба
Received 20 April 2002
