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Occurrence of a rhythmic slower wave in EMG prior to a rapid voluntary movement
Electroencephalograph)' and clinical Neuropl~vsiologv, 1984, 57:435-440 Elsevier Scientific Publishers Ireland, Ltd.
435
O C C U R R E N C E OF A R H Y T H M I C S L O W E R WAVE IN EMG PRIOR TO A RAPID V O L U N T A R Y MOVEMENT KATSUNORI TANII
Department of Human Factors Engineering, Industrial Pr~,ducts Research Institute, Tsukuba Science City, lbaraki 305 (Japan) (Accepted for publication: November 4, 1983)
The normal functioning of the deep muscles of the back during various exercises has been studied (Pauly 1966). Floyd and Silver (1951) first showed that the erector spinal muscles became electromyographically inactive in a fully bent posture. Tanii (1983) reported that the silent period prior to movement, which has been observed only in the arm and leg muscles prior to a reaction movement (Ikai 1955; Yabe 1976), was recorded from the erector spinal muscles prior to a rapid straightening-up movement with and without an external signal. In addition, he mentioned that a rhythmic slower wave in the muscle, with a periodicity (i.e., the interval between EMG peaks) of 20-30 rasec, was recorded sometimes from all subjects about 100 msec before the phasic discharge in both reaction movement and self-paced movement and the silence was not observed. A surface EMG similar to the rhythmic slower wave is seen in EMG recordings obtained by Mita et al. (1982) and Kawahatsu and Hata (1982), but this surface EMG has not quite been mentioned. In the previous study (Tanii 1983), it was found that the silence when the subject lifted a weight occurred more frequently than when the movement was performed without any external load, and that the duration of the silence when lifting a weight was longer than when no load was lifted. It was suggested, therefore, that the silence is related to motor preparation for a more forceful contraction with faster rates of contraction, rather than only to the speed of muscle contraction. In this study the frequency of the appearance of the rhythmic slower wave in the erector spinal muscles in self-paced movement was examined under 3 conditions, in order to investigate a relationship
between the rhythmic slower wave and the motor preparation.
Methods
Experimental procedures Five male subjects aged 22-37 years participated in this study. They were not the same subjects as in the previous study (Tanii 1983), except for one. The straightening-up movement from a moderately bent angle of 50 ° in the sagittal plane was performed rapidly with straight knees and moderately straight back under 3 conditions: without any external load; with an additional load suspended by the hands; and lifting a load from a platform in front of the subject as quickly as possible. The subject could begin freely the rapid movement under each condition whenever he was fully ready for the beginning of the movement after he held the bent posture, and was asked no change of the bent posture during the preparatory phase. As result, most of the durations of the preparatory phase (about 75%) ranged between 4 sec and 6 sec. The height of the platform was adjusted to the height of each subject. In the third condition, the load of the lumbar region increases abruptly while straightening up. Weights of 2.5, 5.0, 10.0, 15.0 and 20.0 kg were used as loads. The trial order of weights, which was predetermined at random, included no external load (0.0 kg) and differed among the 5 subjects. The movement was repeated 10 times for each weight under the same conditions and also with no load. The subjects paused sometimes during the series of 10 trials. During the preparatory
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
K. TANII
436
phase and performances the elbows were straightened, the feet were kept flat on the floor and the legs were spread about 10 cm apart to increase the stability of the body.
Results
The rhythmic slower wave in the erector spinal muscle (L4) was often observed in two subjects who showed lower frequency of the silence in the muscle than other subjects, and sometimes in one of the other subjects. The two subjects were not studied in the previous study (Tanii 1983), Averaged frequency of the silence for the two subjects was 10.9% and 55.5%. That for the other 3 subjects was 86.4%, 78.2% and 94.5%. The silence sometimes followed after the rhythmic slower wave. The frequency of the occurrence of the slower wave for one of the two subjects who often showed the slower wave was 80.0% in the condition without any external load, 38.0% in the condition with an additional load, and 36.0% in the condition lifting a load, including the slower wave which was followed by the silence. The frequency of the slower wave for the other subject was 40.0%, 46.0% and 60.0%, respectively. Thus individual difference in
Recordings Bipolar surface EMGs of the erecto: spinal muscle at the level of the first and the fourth lumbar vertebrae (El and L4 level), the gluteus maximus muscle and the semitendinosus muscle on the right side were led by a pair of miniature biopotential skin electrodes (Beckman) with a time constant of 0.03 sec. The paired electrodes were attached to the skin by double adhesive tape about 2 cm apart above the muscles. The EM(}~ were recorded on a chart with a speed of 100 inm/sec or 200 m m / s e c and simultaneously on magnetic tape. The signal from a goniometer attached to the skin on the trochanter major by adhesive tape was measured simultaneously to identify the period of the rapid straightening-up movement.
I
0.50 mV
Erect. sp. (L4)
,
~,I
Glut. max.
Semitend.
Goniometer output
j I~"---'--"-~
, '
,
!
.
I
,
.
.
.
] !
.~
i/
i
] 0.50 mV
mV
I
' ~ i # ~
100 mcec Fig. 1. Change of surface EMG in the preparatory phase to the slower wave (underlined) before the movement. The arrow above the
top EMG tracing shows the apparent change of EMG activity. The deflection of the bottom line indicates the beginning of the movement. This chart was obtained from subject FS while st~raighteningup under no external load conditions.
EMG SLOWER WAVE PRIOR TO VOLUNTARY MOVEMENT
the frequency of the slower wave in each load condition was great. A relationship between the frequency of the slower wave and the graduated loading was not found. The rhythmic slower wave was often recorded a few hundred milliseconds before the movement. Fig. 1 shows the occurrence of the slower wave before the silent period in the erector spinal muscle prior to the movement and before the phasic discharge of the semitendinosus muscle. The occurrence of the slower wave in the erector spinal muscle was about 200 msec before the movement. In the semitendinosus muscle, the change ~:o the slower wave was more drastic and occurred about 320 msec before the beginning of movement. In addition, the activity of the erector spinal muscle (L1) in the preparatory phase also began changing 590 msec before the movement. The amplitude of the E M G after the change of the muscle activity increased. The signal from the hip goniometer did not change simultaneously with the appearance of the slower wave. A typical recording of the increase of the ampli--
Erect. sp.(L1) Erect. sp. _
!
,,
437
tude of the slower wave is illustrated in Fig. 2. Sharply projected E M G peaks were seen before the silent period in the erector spinal muscle at the L1 level prior to the movement. The surface E M G of the erector spinal muscle at the L1 level during the sustained contraction changed suddenly to the slower wave about 450 msec before the movement. The surface E M G of the erector spinal muscle at the L4 level and the gluteus muscle also changed about 450 msec before the movement. The activity of the semitendinosus muscle in the preparatory phase decreased suddenly before the phasic discharge. Fig. 3 shows the continuous transition of the slower wave to the phasic discharge. The slower wave was seen in the erector spinal muscles and the semitendinosus muscle about 300 msec before the phasic discharge, The amplitude of the slower wave in the erector spinal muscles increased, especially before the phasic discharge. The E M G recordings reported here indicate that the periodicity of 20-30 msec in the rhythmic slower wave did not differ among the prime mover muscles and between subjects.
,t i
ti, ',:, / LtAi
,.,
;l'l ilv v
(L J
,, '.i.
Glut. max.
.v , - , , ', ~ ~ ' ~ ~ ' V
,
~/~"'~
Semitend.
] 0.25 mV
,/') ii!
"t;/J/h~'~'7'#v"lw"t/~q"t~/'l'A%~Vf+'
'I i'!tt!}~l,y,~,~.,,.-~ ] 0.50rnV
Goniometer output I
I
100 msec
i ~
Fig. 2. Increase of the amplitude of the slower wave which was observed in the erector spinal muscle (LI). The arrow above the top EMG trace shows the sudden change of the activity of the erector spinal muscle at the L1 level in the preparatory phase. Oscillograph traces were measured from subject SM while he was lifting a t0 kg weight.
438
K. TA N II
Erect. sp. (L 1 )
~ ~
i
] 0.5 mV
i
Erect. sp. (1_4}
/
bemutena.
Goniometer
1
output
,
I .
,
iii i
!
200 msec Fig. 3. EMGs showing a continuous transition from tht slower wave to the phasic discharge. EMG traces were obtained from subject FS when an additional load of 20 kg was carried by th,,• hands.
Discussion
In the present study, the rhythmic slower wave was recorded from the trunk muscle and the leg muscle and no individual difference in the regular periodicity of the slower wave was confirmed. No relationship between the frequency of the rhythmic slower wave in the erector spinal muscle (L4) and the graduated loading was found and the load conditions also were not related to the frequency of the slower wave. The lack of a change of signal from the hip-joint goniometer before and during the slower wave and the silence indicates that both phenomena did not result from the change of the moderately bent posture during the preparatory phase. However, the adjustment of small movements between individual vertebrae a n d / o r the stabilization of the vertebral column by the transversospinal muscles (Donisch and Basmajian 1972) might be occurring prior to the movement. Although so, the intervertebral movements a n d / o r stabilization will not contribute directly to the
slower wave, because the slower wave occurred in both the erector spinal muscle and the semitendinosus muscle. The earlier occurrence of the slower wave than expected and the simultaneous occurrence of the slower wave in the prime movers seem to suggest that the slower wave may be related to motor preparation to perform the rapid self-paced movement. In the earlier study (Tanii 1983), the obvious change of the amplitude of the slower wave was not observed• In the present study, the increase of the amplitude of the slower wave and the pattern of the continuous transition of the slower wave to the phasic discharge which motor units tend to synchronize allow the slower wave to associate with synchronization between motor units. It seems, presumably, that the slower waves reflect a degree of synchronization of motor unit activity. The occurrence of the silence in the erector spinal muscle (Tanii 1983, the present results) and Yabe's (1976) findings suggest that the silence is not explained by reciprocal inhibition• Yabe (1976)
EMG SLOWER WAVE PRIOR TO VOLUNTARY MOVEMENT found no burst of the antagonist muscle when the silence occurred prior to distinct bursts of the agonist muscle. Probably the silence is inhibition of cortical origin. Recently it was reported that supraspinal convergence on Renshaw cells allows recurrent inhibition to serve as a variable gain regulator at motoneuronal level during contractions (Hultborn et al. 1979). Therefore st~ch a mechanism may contribute to the silence and the decrease of the E M G amplitude prior to the phasic discharge and may interrupt the occurrence of the slower wave, which suggests a significant change of spinal motoneurons. Individual differences in the frequency of the silence and the slower ~ave may be interpreted by an individual difference in the excitatory convergence onto Renshaw cells from supraspinal pathways. However, a conwibution of supraspinal convergence on Renshaw cells to the occurrence of the rhythmic slower ~ave cannot be disregarded, because no difference in the periodicity of the slower wave among the prime movers and among subjects may be due to firing of only motor units with the same contractile property, that is, of the same type of alpha motoneurons. In the present study it was suggested that the rhythmic slower wave which presumably reflected a significant change of motoneuronal activit5 might occur in connection with motor preparation for the rapid voluntary movement.
Summaff The aim of the present study was to investigate whether an E M G slower wave prior to a rapid straightening-up movement is associated with motor preparation to perform the movement. The straightening movement was performed at 6 load intensities and under 3 conditions: without any external load; with an additional load; lifting a load. The subject could freely begin the rapid movement from a moderate forward-bending position whenever he was fully ready for the beginning of the movement after he held the bent posture. Bipolar surface E M G s of the erector spinal muscles at the L1 and L4 level, the gluteus maximus muscle and the semitendinosus muscle were led by a pair
439 of skin electrodes with a time constant of 0.03 sec. The signal from the hip goniometer was measured simultaneously to identify the period of the movement. A distinct relationship between the occurrence of the slower wave and both load intensities and conditions was not found. However, the rhythmic slower wave often occurred in the muscles 200-450 msec before the movement. The occurrence of the wave in the muscles was often simultaneous. The signal from the hip goniometer did not change with the occurrence of the slower wave. The amplitude of the slower wave increased frequently. The present results suggest that the slower wave may reflect a significant change of motoneuronal activity in connection with motor preparation to perform the movement.
Resume Apparition d'une onde rythmique lente dans I'EMG prbcbdant un mouvement volontaire rapide Le but de la pr6sente 6tude a 6t6 de rechercher si une onde E M G lente, pr6c~dant un mouvement rapide de redressement, se trouve associ6e avec la pr6paration motrice ~ effectuer ce mouvement. Le mouvement de redressement a 6t6 effectu6 avec 6 intensit6s de charges diff6rentes et dans 3 conditions: sans charge ext6rieure, avec charge additionnelle, et en soulevant une charge. Le sujet pouvait commencer son mouvement rapide h volont6 partir d'une position 16g~rement pench6e vers l'avant, d~s qu'il ~tait totalement pr~t h d6marrer ce mouvement rapide apr6s prise de la posture pench6e. Des E M G bipolaires de surface ont 6t6 recueillis sur les muscles erectores spinae aux niveaux L1 et L4, sur le muscle gluteus maximus et sur le semitendineux par une paire d'61ectrodes cutan6es, avec une constante de temps de 0,03 sec. Le signal du goniom6tre de la hanche a 6t~ mesur6 simultan6ment pour identifier la p6riode du mouvement. Une relation nette a 6t6 trouv6e entre l'apparition de l'onde lente d'une part et d'autre part, h la fois les intensit6s de charges et les conditions exp6rimentales. Toutefois, l'onde rythmique lente
440
est souvent apparue dans les muscles 200-450 msec avant le mouvement. L'apparition de cette onde dans les divers muscles 6tait souvent simultan6e. Le signal du goniom6tre de la hanche n'a pas 6t6 modifi6 lors de l'apparition de l'onde lente. L'amplitude de cette onde lente augmentait fr6quemment. Ces r6suhats sugg6rent que cette onde lente peut Etre le reflet d'une modification significative de l'activit6 des motoneurones en connexion avec la pr6paration motrice h effectuer le mouvement.
References Donisch, E.W. and Basmajian, J.V. Electromyography of deep muscles in man, Amer. J. Anat., 1972, 133: 25-3~,. Floyd, W.F. and Silver, P.H.S. Function of the erecto-e~, spinae in flexion of the trunk. Lancet, 1951, 2 6 0 : 1 3 3 - 1 5 4
K. TANII Hultborn, H., LindstrOm, S. and Wigstr6m, H. On the function of recurrent inhibition in the spinal cord. Exp. Brain Res., 1979, 37: 399-403. lkai, M. Inhibition as an accompaniment of rapid voluntary act (in Japanese). J. Physiol. Soc. Jap., 1955, 17: 292-298. Kawahatsu, K. and Hata, Y. Feature of EMG premotion silent period from the viewpoint of a motor control (in Japanese). J. phys. Fitness Jap., 1982, 31: 1-9. Mita, K., Aoki, H. and Yabe, K. Variability of electromyogram prior to a reaction movement in man (in Japanese). J. phys. Fitness Jap., 1982, 31: 234-241. Pauly, J.E. An electromyographic analysis of certain movements and exercises. 1. Some deep muscles of the back. Anat, Rec., 1966, 155: 223-234. Tanii, K. An electromyographic silent period in the erectores spinae prior to a rapid straightening up movement (in Japanese). J. antbrop. Soc. Nippon, 1983, 9 1 : 1 1 - 2 4 . Yabe, K. Premotion silent period in rapid voluntary movement. J. appl. Physiol., 1976, 41: 470-473.
435
O C C U R R E N C E OF A R H Y T H M I C S L O W E R WAVE IN EMG PRIOR TO A RAPID V O L U N T A R Y MOVEMENT KATSUNORI TANII
Department of Human Factors Engineering, Industrial Pr~,ducts Research Institute, Tsukuba Science City, lbaraki 305 (Japan) (Accepted for publication: November 4, 1983)
The normal functioning of the deep muscles of the back during various exercises has been studied (Pauly 1966). Floyd and Silver (1951) first showed that the erector spinal muscles became electromyographically inactive in a fully bent posture. Tanii (1983) reported that the silent period prior to movement, which has been observed only in the arm and leg muscles prior to a reaction movement (Ikai 1955; Yabe 1976), was recorded from the erector spinal muscles prior to a rapid straightening-up movement with and without an external signal. In addition, he mentioned that a rhythmic slower wave in the muscle, with a periodicity (i.e., the interval between EMG peaks) of 20-30 rasec, was recorded sometimes from all subjects about 100 msec before the phasic discharge in both reaction movement and self-paced movement and the silence was not observed. A surface EMG similar to the rhythmic slower wave is seen in EMG recordings obtained by Mita et al. (1982) and Kawahatsu and Hata (1982), but this surface EMG has not quite been mentioned. In the previous study (Tanii 1983), it was found that the silence when the subject lifted a weight occurred more frequently than when the movement was performed without any external load, and that the duration of the silence when lifting a weight was longer than when no load was lifted. It was suggested, therefore, that the silence is related to motor preparation for a more forceful contraction with faster rates of contraction, rather than only to the speed of muscle contraction. In this study the frequency of the appearance of the rhythmic slower wave in the erector spinal muscles in self-paced movement was examined under 3 conditions, in order to investigate a relationship
between the rhythmic slower wave and the motor preparation.
Methods
Experimental procedures Five male subjects aged 22-37 years participated in this study. They were not the same subjects as in the previous study (Tanii 1983), except for one. The straightening-up movement from a moderately bent angle of 50 ° in the sagittal plane was performed rapidly with straight knees and moderately straight back under 3 conditions: without any external load; with an additional load suspended by the hands; and lifting a load from a platform in front of the subject as quickly as possible. The subject could begin freely the rapid movement under each condition whenever he was fully ready for the beginning of the movement after he held the bent posture, and was asked no change of the bent posture during the preparatory phase. As result, most of the durations of the preparatory phase (about 75%) ranged between 4 sec and 6 sec. The height of the platform was adjusted to the height of each subject. In the third condition, the load of the lumbar region increases abruptly while straightening up. Weights of 2.5, 5.0, 10.0, 15.0 and 20.0 kg were used as loads. The trial order of weights, which was predetermined at random, included no external load (0.0 kg) and differed among the 5 subjects. The movement was repeated 10 times for each weight under the same conditions and also with no load. The subjects paused sometimes during the series of 10 trials. During the preparatory
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
K. TANII
436
phase and performances the elbows were straightened, the feet were kept flat on the floor and the legs were spread about 10 cm apart to increase the stability of the body.
Results
The rhythmic slower wave in the erector spinal muscle (L4) was often observed in two subjects who showed lower frequency of the silence in the muscle than other subjects, and sometimes in one of the other subjects. The two subjects were not studied in the previous study (Tanii 1983), Averaged frequency of the silence for the two subjects was 10.9% and 55.5%. That for the other 3 subjects was 86.4%, 78.2% and 94.5%. The silence sometimes followed after the rhythmic slower wave. The frequency of the occurrence of the slower wave for one of the two subjects who often showed the slower wave was 80.0% in the condition without any external load, 38.0% in the condition with an additional load, and 36.0% in the condition lifting a load, including the slower wave which was followed by the silence. The frequency of the slower wave for the other subject was 40.0%, 46.0% and 60.0%, respectively. Thus individual difference in
Recordings Bipolar surface EMGs of the erecto: spinal muscle at the level of the first and the fourth lumbar vertebrae (El and L4 level), the gluteus maximus muscle and the semitendinosus muscle on the right side were led by a pair of miniature biopotential skin electrodes (Beckman) with a time constant of 0.03 sec. The paired electrodes were attached to the skin by double adhesive tape about 2 cm apart above the muscles. The EM(}~ were recorded on a chart with a speed of 100 inm/sec or 200 m m / s e c and simultaneously on magnetic tape. The signal from a goniometer attached to the skin on the trochanter major by adhesive tape was measured simultaneously to identify the period of the rapid straightening-up movement.
I
0.50 mV
Erect. sp. (L4)
,
~,I
Glut. max.
Semitend.
Goniometer output
j I~"---'--"-~
, '
,
!
.
I
,
.
.
.
] !
.~
i/
i
] 0.50 mV
mV
I
' ~ i # ~
100 mcec Fig. 1. Change of surface EMG in the preparatory phase to the slower wave (underlined) before the movement. The arrow above the
top EMG tracing shows the apparent change of EMG activity. The deflection of the bottom line indicates the beginning of the movement. This chart was obtained from subject FS while st~raighteningup under no external load conditions.
EMG SLOWER WAVE PRIOR TO VOLUNTARY MOVEMENT
the frequency of the slower wave in each load condition was great. A relationship between the frequency of the slower wave and the graduated loading was not found. The rhythmic slower wave was often recorded a few hundred milliseconds before the movement. Fig. 1 shows the occurrence of the slower wave before the silent period in the erector spinal muscle prior to the movement and before the phasic discharge of the semitendinosus muscle. The occurrence of the slower wave in the erector spinal muscle was about 200 msec before the movement. In the semitendinosus muscle, the change ~:o the slower wave was more drastic and occurred about 320 msec before the beginning of movement. In addition, the activity of the erector spinal muscle (L1) in the preparatory phase also began changing 590 msec before the movement. The amplitude of the E M G after the change of the muscle activity increased. The signal from the hip goniometer did not change simultaneously with the appearance of the slower wave. A typical recording of the increase of the ampli--
Erect. sp.(L1) Erect. sp. _
!
,,
437
tude of the slower wave is illustrated in Fig. 2. Sharply projected E M G peaks were seen before the silent period in the erector spinal muscle at the L1 level prior to the movement. The surface E M G of the erector spinal muscle at the L1 level during the sustained contraction changed suddenly to the slower wave about 450 msec before the movement. The surface E M G of the erector spinal muscle at the L4 level and the gluteus muscle also changed about 450 msec before the movement. The activity of the semitendinosus muscle in the preparatory phase decreased suddenly before the phasic discharge. Fig. 3 shows the continuous transition of the slower wave to the phasic discharge. The slower wave was seen in the erector spinal muscles and the semitendinosus muscle about 300 msec before the phasic discharge, The amplitude of the slower wave in the erector spinal muscles increased, especially before the phasic discharge. The E M G recordings reported here indicate that the periodicity of 20-30 msec in the rhythmic slower wave did not differ among the prime mover muscles and between subjects.
,t i
ti, ',:, / LtAi
,.,
;l'l ilv v
(L J
,, '.i.
Glut. max.
.v , - , , ', ~ ~ ' ~ ~ ' V
,
~/~"'~
Semitend.
] 0.25 mV
,/') ii!
"t;/J/h~'~'7'#v"lw"t/~q"t~/'l'A%~Vf+'
'I i'!tt!}~l,y,~,~.,,.-~ ] 0.50rnV
Goniometer output I
I
100 msec
i ~
Fig. 2. Increase of the amplitude of the slower wave which was observed in the erector spinal muscle (LI). The arrow above the top EMG trace shows the sudden change of the activity of the erector spinal muscle at the L1 level in the preparatory phase. Oscillograph traces were measured from subject SM while he was lifting a t0 kg weight.
438
K. TA N II
Erect. sp. (L 1 )
~ ~
i
] 0.5 mV
i
Erect. sp. (1_4}
/
bemutena.
Goniometer
1
output
,
I .
,
iii i
!
200 msec Fig. 3. EMGs showing a continuous transition from tht slower wave to the phasic discharge. EMG traces were obtained from subject FS when an additional load of 20 kg was carried by th,,• hands.
Discussion
In the present study, the rhythmic slower wave was recorded from the trunk muscle and the leg muscle and no individual difference in the regular periodicity of the slower wave was confirmed. No relationship between the frequency of the rhythmic slower wave in the erector spinal muscle (L4) and the graduated loading was found and the load conditions also were not related to the frequency of the slower wave. The lack of a change of signal from the hip-joint goniometer before and during the slower wave and the silence indicates that both phenomena did not result from the change of the moderately bent posture during the preparatory phase. However, the adjustment of small movements between individual vertebrae a n d / o r the stabilization of the vertebral column by the transversospinal muscles (Donisch and Basmajian 1972) might be occurring prior to the movement. Although so, the intervertebral movements a n d / o r stabilization will not contribute directly to the
slower wave, because the slower wave occurred in both the erector spinal muscle and the semitendinosus muscle. The earlier occurrence of the slower wave than expected and the simultaneous occurrence of the slower wave in the prime movers seem to suggest that the slower wave may be related to motor preparation to perform the rapid self-paced movement. In the earlier study (Tanii 1983), the obvious change of the amplitude of the slower wave was not observed• In the present study, the increase of the amplitude of the slower wave and the pattern of the continuous transition of the slower wave to the phasic discharge which motor units tend to synchronize allow the slower wave to associate with synchronization between motor units. It seems, presumably, that the slower waves reflect a degree of synchronization of motor unit activity. The occurrence of the silence in the erector spinal muscle (Tanii 1983, the present results) and Yabe's (1976) findings suggest that the silence is not explained by reciprocal inhibition• Yabe (1976)
EMG SLOWER WAVE PRIOR TO VOLUNTARY MOVEMENT found no burst of the antagonist muscle when the silence occurred prior to distinct bursts of the agonist muscle. Probably the silence is inhibition of cortical origin. Recently it was reported that supraspinal convergence on Renshaw cells allows recurrent inhibition to serve as a variable gain regulator at motoneuronal level during contractions (Hultborn et al. 1979). Therefore st~ch a mechanism may contribute to the silence and the decrease of the E M G amplitude prior to the phasic discharge and may interrupt the occurrence of the slower wave, which suggests a significant change of spinal motoneurons. Individual differences in the frequency of the silence and the slower ~ave may be interpreted by an individual difference in the excitatory convergence onto Renshaw cells from supraspinal pathways. However, a conwibution of supraspinal convergence on Renshaw cells to the occurrence of the rhythmic slower ~ave cannot be disregarded, because no difference in the periodicity of the slower wave among the prime movers and among subjects may be due to firing of only motor units with the same contractile property, that is, of the same type of alpha motoneurons. In the present study it was suggested that the rhythmic slower wave which presumably reflected a significant change of motoneuronal activit5 might occur in connection with motor preparation for the rapid voluntary movement.
Summaff The aim of the present study was to investigate whether an E M G slower wave prior to a rapid straightening-up movement is associated with motor preparation to perform the movement. The straightening movement was performed at 6 load intensities and under 3 conditions: without any external load; with an additional load; lifting a load. The subject could freely begin the rapid movement from a moderate forward-bending position whenever he was fully ready for the beginning of the movement after he held the bent posture. Bipolar surface E M G s of the erector spinal muscles at the L1 and L4 level, the gluteus maximus muscle and the semitendinosus muscle were led by a pair
439 of skin electrodes with a time constant of 0.03 sec. The signal from the hip goniometer was measured simultaneously to identify the period of the movement. A distinct relationship between the occurrence of the slower wave and both load intensities and conditions was not found. However, the rhythmic slower wave often occurred in the muscles 200-450 msec before the movement. The occurrence of the wave in the muscles was often simultaneous. The signal from the hip goniometer did not change with the occurrence of the slower wave. The amplitude of the slower wave increased frequently. The present results suggest that the slower wave may reflect a significant change of motoneuronal activity in connection with motor preparation to perform the movement.
Resume Apparition d'une onde rythmique lente dans I'EMG prbcbdant un mouvement volontaire rapide Le but de la pr6sente 6tude a 6t6 de rechercher si une onde E M G lente, pr6c~dant un mouvement rapide de redressement, se trouve associ6e avec la pr6paration motrice ~ effectuer ce mouvement. Le mouvement de redressement a 6t6 effectu6 avec 6 intensit6s de charges diff6rentes et dans 3 conditions: sans charge ext6rieure, avec charge additionnelle, et en soulevant une charge. Le sujet pouvait commencer son mouvement rapide h volont6 partir d'une position 16g~rement pench6e vers l'avant, d~s qu'il ~tait totalement pr~t h d6marrer ce mouvement rapide apr6s prise de la posture pench6e. Des E M G bipolaires de surface ont 6t6 recueillis sur les muscles erectores spinae aux niveaux L1 et L4, sur le muscle gluteus maximus et sur le semitendineux par une paire d'61ectrodes cutan6es, avec une constante de temps de 0,03 sec. Le signal du goniom6tre de la hanche a 6t~ mesur6 simultan6ment pour identifier la p6riode du mouvement. Une relation nette a 6t6 trouv6e entre l'apparition de l'onde lente d'une part et d'autre part, h la fois les intensit6s de charges et les conditions exp6rimentales. Toutefois, l'onde rythmique lente
440
est souvent apparue dans les muscles 200-450 msec avant le mouvement. L'apparition de cette onde dans les divers muscles 6tait souvent simultan6e. Le signal du goniom6tre de la hanche n'a pas 6t6 modifi6 lors de l'apparition de l'onde lente. L'amplitude de cette onde lente augmentait fr6quemment. Ces r6suhats sugg6rent que cette onde lente peut Etre le reflet d'une modification significative de l'activit6 des motoneurones en connexion avec la pr6paration motrice h effectuer le mouvement.
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