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Effects of head position on static and dynamic responses of the lower limbs
Clin. Biomech.
1993; 8: 109- 111
Brief Report
Effects of head position on static and dynamic responses of the lower limbs S T E ke-Okoro Department
Dr Med Sci
of Medical Rehabilitation,
University
of Nigeria, Nigeria
Summary The changes in H-max amplitudes and gaits of seven normal subjects were studied when they adopted different head positions. It was seen that in a static state the adopted head positions effectively altered the pattern of H-reflex transmission in the lower limbs. The head position did not significantly affect the parameters of gait. It is suggested that the changes in H-max amplitude in the lower limbs in a static state were due to the influence of tonic neck and labyrinthine reflexes, and that in the dynamic situation such influences may have been eclipsed by the activation of other neural factors.
Relevance The results may be helpful in a better understanding of the role, if any, of the tonic neck and labyrinthine reflexes in gait, and how the reflexes could interact with at least the cervical network of neurons responsible for the generation of the arm movements of gait. Key words: Reflexes, H-max, gait, head position, neural interaction
Introduction
The neural relationship between the lumbar and cervical enlargements of the spinal cord has recently attracted the attention of many workers in an attempt to relate the biomechanics of the upper and lower limbs’,*. These studies have been in the relaxed state and the results could not be effectively applied to a dynamic situation such as gait. However, in the rabbit a clear evidence of interaction between the lumbar and cervical neural networks - so-called gait generators3 - has been shown4. The generator concept of gait explains that the lower limb muscles are controlled by the lumbosacral generator, while upper limb muscles are controlled by the cervical generator. The interaction of the two generators during gait found in animals4 has been difficult to demonstrate in humans. However, it has been shown that changes in arm positions during gait alter the duration of the double support phase of gait stride (Eke-Okoro, unpublished data). The present study examined how
Received: 16 August 1991 Accepted: 27 March 1992 Correspondence and reprint requests to: S T Eke-Okoro, Department of Medical Rehabilitation, College of University of Nigeria, Enugu Campus, Nigeria 0 1993 Butterworth-Heinemann 0268-0033/93/020109-03
Ltd
or Med SCI, Medicine,
the static reflex responses of the lower limbs could be related to dynamic gait parameters. The effects of head position on tibia1 nerve H-reflex of the calf and effects of similar head positions on gait were examined in normal human subjects. An alteration in head position would affect the position of the centre of mass of the body; the tibialnerve H-reflex (elicited from the calf muscles) is a postural reflex and the changes of the phases of stride usually indicate the pattern of postural adjustments in gait. This is because a postural change in one part of the body is usually compensated for by an appropriate change in another part. It was therefore hypothesized that such postural changes in head position would be reflected in the lower limbs in both the reflex and gait tests. Methods
The subjects were six males and one female normal undergraduate students with an age range of 24-40 years and a mean age of 31 (SD 7) years. The height range was 1.59 to 1.73 m, with a mean of 1.68 (SD O.Oijm. H-reflex elicitation
Each subject sat on a chair and rested the lower limbs on a pillow placed on a stool in front of the chair, so
110
Clin. Biomech.
1993; 8: No 2
that the knees were fully extended. The lower limbs were 15 cm apart, and were supported to avoid rotation about their neutral positions. A small cathode electrode (3-cm diameter) was placed directly under the tibia1 nerve in the popliteal fossa, while a larger anode (5-cm diameter) was placed on the knee. The EMG surface electrodes (l-cm diameter) were placed at the lower border of the calf. The ground electrode (lo-cm diameter) was placed on the calf between the stimulating and the surface EMG electrodes. All electrodes were fixed in position by means of adhesive straps. The stimulating electrodes were connected to a Medelex IS/V isolated nerve stimulator from which a stimulus of 1 ms duration was drawn. The EMG and the ground electrodes were connected to an MS6 AC amplifier (AA6M). These were parts of a Medelec MSC unit. The stimulus was 1 pulse/s and the current voltage was within the range of 50-55 V. The reflex response appeared on the oscilloscope of the Medelec unit. The sensitivity of the EMG amplifier was mostly 500 PV per division with a sweep duration of 10 ms per division. The low and high cut-off frequencies were 8 Hz and 3.2 kHz respectively. A peak-to-peak amplitude average of 20 responses in each case of the H-max was obtained in the following head positions: (i) The neck was flexed to the right so that the head was close to the right shoulder (HDR); (ii) the neck was flexed to the left so that the head was close to the left shoulder (HDL); (iii) the neck was flexed forward so that the face looked down (HDF); (iv) the neck was extended backward so that the face looked up (HDB). The control was obtained with the head in the normal erect position and with the arms relaxed by the sides. The H-reflex was elicited from both calves.
Table 1. Right and left tibia1 nerve H-max (mV) of adopted head positions (n = 7)
amplitudes
H-max
CTR
HDR
HDL
HDF
HDB
Right SD
1.76 0.21
1.80 0.23
1.73 0.23
1.74 0.21
1.90 0.27
Left
1.52 0.26
1.30 0.51
1.79 0.34
1.14 0.50
1.68 0.29
+
+
n.s.
SD
P
+
+
CTR, control; HDR, head to the right; HDL, head to the left; HDF, head forward; HDB, head backward; +, values used for statistical analysis. For a more detailed description of the abbreviations, see text.
Results
The values of H-max amplitudes with respect to the head positions and the side of stimulation are shown in Table 1. When the right tibia1 nerve was stimulated, the peak-to-peak H-max amplitude (Figure 1) was facilitated as the neck was flexed to the right (HDR) and when extended backward (HDB). The H-max was slightly depressed when the neck was either flexed to the left (HDL) or forward (HDF). Stimulation of the left tibia1 nerve resulted in increased H-max in HDL and HDB. The wave was depressed in HDR and HDF in left nerve stimulation. H-max was generally larger in size when the right leg was stimulated than in left-leg stimulation. H-max was potentiated in HDB and depressed in HDF irrespective of the side of stimulation. In gait analysis, the adopted head positions did not cause any significant changes in the parameters of gait. There were marginal differences in the phases of stride between the legs, but the differences were not statistically significant. Velocity, stride length, and stride frequency did not show any consistent pattern and the differences between the control and test situations were not statistically significant in all cases.
Gait registration
Discussion
Walking patterns were studied in a gait laboratory by means of foot switches after the reflex tests; the subjects adopted the above head positions as they walked. Each subject was asked to walk with five speeds: very slow, slow, ordinary, fast and very fast for each head position. Details of the recording method have previously been described5. Briefly, the subjects wore socks, the soles of which were plastic and rough. Electrically conductive adhesive tapes were fastened to the ball and heel of each foot. Wires from the tapes ran to a channelling box strapped to the subject’s lower back. Connection to the main equipment was made by a long cable which passed through a frictionless pulley in the ceiling and followed the subject as he walked. As the subject walked along the 10-m walkway, which was covered with a metal gauze, the conductive tapes formed four switches which opened and closed during the stride. This arrangement made it possible for the computer to record the duration of the phases of the stride. Statistical calculations were by means of paired t-test in all cases.
In the static condition, changes in head position were able to alter the pattern of reflex responses in the lower H-max
0.2 mV 20 ms
Figure 1 A printout showing H-max resulting from one of the adopted head positions. S, stimulus; M, direct muscle response (the M-wave). With increasing stimulus voltage, the amplitude of the H-wave declines, while the M-wave appreciates.
Eke-Okoro:
limbs. It can be said that there is interaction between the lumbar and cervical regions of the spinal cord in the static situation of H-reflex experiments, possibly through propriospinal neuron connection’. The reflex responses also show some side difference between the left and right legs. The H-max was augmented in right tibia1 nerve stimulation when compared to left tibia1 nerve stimulation for most of the head positions. This pattern may have resulted from a righting response related to the influence of tonic neck and labyrinthine reflexes2. It was expected that the significant influence of the head positions on reflex transmisssion in the lower limbs could have been seen in the gait situation. This means that the hypothesis of this study was supported only in the reflex experiment but not in gait. An explanation for this result may be that the static reflex experimental situation could not be effectively related to the dynamic gait situation. In a previous study it was shown that changes in arm position significantly affected gait parameters (EkeOkoro, unpublished data). The implication may be that the gait generators were directly stimulated, since they control the upper and lower limbs respectively6. Again, in a static situation changes in arm position have been shown to alter the pattern of reflex transmission in the lower limbs’. In the present experiments the effects of head position on gait (a dynamic action) may have been
Head position
and lower limb responses
111
resulting from any alteration in head position. Perhaps the postural displacement of the centre of mass of the body resulting from alterations in head position may have been compensated for proximally during arm swing, instead of distally during foot stride of gait. Further studies need to be done to explain this phenomenon. Acknowledgement This study was supported with Senate Research Grant (90/30) of the University of Nigeria.
References Delwaide PJ, Figiel C, Richelle C. Effects of postural changes in the upper limb on reflex transmission in the lower limbs. J Neurol Neurosurg Psychiatry 1977; 40: 616-21
Hayes KC, Sullivan J. Tonic neck reflex influences on tendon and Hoffman reflexes in man. Electromyogr Clin Neurophysiol
1976; 16: 251-61
eclipsed by neural factors activated during stride movements. Such neural factors would compensate for
Brown TG. The intrinsic factors in the act of propression in the mammal. Proc R Sot B 1911; 84: 308-19 Viala D, Vidal C. Evidence for distinct spinal locomotion generators supplying respectively fore- and hindlimbs in the rabbit. Brain Res 1978; 155: 182-6 Larsson LE, Odenrick P, Sandlund B, Weitz P, Oberg PA. The phases of the stride and their interaction in human gait. Stand J Rehabil Med 1980; 12: 107-12 Eke-Okoro ST. Functional dispositions of the spinal stepping generators and their half-centres. Electromyogr
even the smallest dislodgement
Clin Neurophysiol
of the centre of mass
1991; 31: 81-3
The 6th International Symposium of the Physical Medicine Research Foundation organized in association with
The Czech Society of Musculoskeletal Medicine Prague, Czechoslovakia 4-6 June 1993 The symposium will include invited lectures, free papers, and poster presentations, which will be augmented by an extensive satellite programme of clinical workshops and discussion groups. The main scientific sessions will be accompanied by a technical and pharmaceutical exhibition. For further information please contact the relevant secretariat: North American Secretariat Physical Medicine Research Foundation Suite 501, 207 West Hastings Street Vancouver, BC V6B 1H7 Canada
European Secretariat Czech Medical Society Sokolskrl 3 1 120 26 Praha 2 Czechoslovakia
Tel: +604 684 4148 Fax: +604 684 6247
Tel: +42 2 29 68 89 Fax: +42 2 235 24 12 or +42 2 29 46 10
1993; 8: 109- 111
Brief Report
Effects of head position on static and dynamic responses of the lower limbs S T E ke-Okoro Department
Dr Med Sci
of Medical Rehabilitation,
University
of Nigeria, Nigeria
Summary The changes in H-max amplitudes and gaits of seven normal subjects were studied when they adopted different head positions. It was seen that in a static state the adopted head positions effectively altered the pattern of H-reflex transmission in the lower limbs. The head position did not significantly affect the parameters of gait. It is suggested that the changes in H-max amplitude in the lower limbs in a static state were due to the influence of tonic neck and labyrinthine reflexes, and that in the dynamic situation such influences may have been eclipsed by the activation of other neural factors.
Relevance The results may be helpful in a better understanding of the role, if any, of the tonic neck and labyrinthine reflexes in gait, and how the reflexes could interact with at least the cervical network of neurons responsible for the generation of the arm movements of gait. Key words: Reflexes, H-max, gait, head position, neural interaction
Introduction
The neural relationship between the lumbar and cervical enlargements of the spinal cord has recently attracted the attention of many workers in an attempt to relate the biomechanics of the upper and lower limbs’,*. These studies have been in the relaxed state and the results could not be effectively applied to a dynamic situation such as gait. However, in the rabbit a clear evidence of interaction between the lumbar and cervical neural networks - so-called gait generators3 - has been shown4. The generator concept of gait explains that the lower limb muscles are controlled by the lumbosacral generator, while upper limb muscles are controlled by the cervical generator. The interaction of the two generators during gait found in animals4 has been difficult to demonstrate in humans. However, it has been shown that changes in arm positions during gait alter the duration of the double support phase of gait stride (Eke-Okoro, unpublished data). The present study examined how
Received: 16 August 1991 Accepted: 27 March 1992 Correspondence and reprint requests to: S T Eke-Okoro, Department of Medical Rehabilitation, College of University of Nigeria, Enugu Campus, Nigeria 0 1993 Butterworth-Heinemann 0268-0033/93/020109-03
Ltd
or Med SCI, Medicine,
the static reflex responses of the lower limbs could be related to dynamic gait parameters. The effects of head position on tibia1 nerve H-reflex of the calf and effects of similar head positions on gait were examined in normal human subjects. An alteration in head position would affect the position of the centre of mass of the body; the tibialnerve H-reflex (elicited from the calf muscles) is a postural reflex and the changes of the phases of stride usually indicate the pattern of postural adjustments in gait. This is because a postural change in one part of the body is usually compensated for by an appropriate change in another part. It was therefore hypothesized that such postural changes in head position would be reflected in the lower limbs in both the reflex and gait tests. Methods
The subjects were six males and one female normal undergraduate students with an age range of 24-40 years and a mean age of 31 (SD 7) years. The height range was 1.59 to 1.73 m, with a mean of 1.68 (SD O.Oijm. H-reflex elicitation
Each subject sat on a chair and rested the lower limbs on a pillow placed on a stool in front of the chair, so
110
Clin. Biomech.
1993; 8: No 2
that the knees were fully extended. The lower limbs were 15 cm apart, and were supported to avoid rotation about their neutral positions. A small cathode electrode (3-cm diameter) was placed directly under the tibia1 nerve in the popliteal fossa, while a larger anode (5-cm diameter) was placed on the knee. The EMG surface electrodes (l-cm diameter) were placed at the lower border of the calf. The ground electrode (lo-cm diameter) was placed on the calf between the stimulating and the surface EMG electrodes. All electrodes were fixed in position by means of adhesive straps. The stimulating electrodes were connected to a Medelex IS/V isolated nerve stimulator from which a stimulus of 1 ms duration was drawn. The EMG and the ground electrodes were connected to an MS6 AC amplifier (AA6M). These were parts of a Medelec MSC unit. The stimulus was 1 pulse/s and the current voltage was within the range of 50-55 V. The reflex response appeared on the oscilloscope of the Medelec unit. The sensitivity of the EMG amplifier was mostly 500 PV per division with a sweep duration of 10 ms per division. The low and high cut-off frequencies were 8 Hz and 3.2 kHz respectively. A peak-to-peak amplitude average of 20 responses in each case of the H-max was obtained in the following head positions: (i) The neck was flexed to the right so that the head was close to the right shoulder (HDR); (ii) the neck was flexed to the left so that the head was close to the left shoulder (HDL); (iii) the neck was flexed forward so that the face looked down (HDF); (iv) the neck was extended backward so that the face looked up (HDB). The control was obtained with the head in the normal erect position and with the arms relaxed by the sides. The H-reflex was elicited from both calves.
Table 1. Right and left tibia1 nerve H-max (mV) of adopted head positions (n = 7)
amplitudes
H-max
CTR
HDR
HDL
HDF
HDB
Right SD
1.76 0.21
1.80 0.23
1.73 0.23
1.74 0.21
1.90 0.27
Left
1.52 0.26
1.30 0.51
1.79 0.34
1.14 0.50
1.68 0.29
+
+
n.s.
SD
P
+
+
CTR, control; HDR, head to the right; HDL, head to the left; HDF, head forward; HDB, head backward; +, values used for statistical analysis. For a more detailed description of the abbreviations, see text.
Results
The values of H-max amplitudes with respect to the head positions and the side of stimulation are shown in Table 1. When the right tibia1 nerve was stimulated, the peak-to-peak H-max amplitude (Figure 1) was facilitated as the neck was flexed to the right (HDR) and when extended backward (HDB). The H-max was slightly depressed when the neck was either flexed to the left (HDL) or forward (HDF). Stimulation of the left tibia1 nerve resulted in increased H-max in HDL and HDB. The wave was depressed in HDR and HDF in left nerve stimulation. H-max was generally larger in size when the right leg was stimulated than in left-leg stimulation. H-max was potentiated in HDB and depressed in HDF irrespective of the side of stimulation. In gait analysis, the adopted head positions did not cause any significant changes in the parameters of gait. There were marginal differences in the phases of stride between the legs, but the differences were not statistically significant. Velocity, stride length, and stride frequency did not show any consistent pattern and the differences between the control and test situations were not statistically significant in all cases.
Gait registration
Discussion
Walking patterns were studied in a gait laboratory by means of foot switches after the reflex tests; the subjects adopted the above head positions as they walked. Each subject was asked to walk with five speeds: very slow, slow, ordinary, fast and very fast for each head position. Details of the recording method have previously been described5. Briefly, the subjects wore socks, the soles of which were plastic and rough. Electrically conductive adhesive tapes were fastened to the ball and heel of each foot. Wires from the tapes ran to a channelling box strapped to the subject’s lower back. Connection to the main equipment was made by a long cable which passed through a frictionless pulley in the ceiling and followed the subject as he walked. As the subject walked along the 10-m walkway, which was covered with a metal gauze, the conductive tapes formed four switches which opened and closed during the stride. This arrangement made it possible for the computer to record the duration of the phases of the stride. Statistical calculations were by means of paired t-test in all cases.
In the static condition, changes in head position were able to alter the pattern of reflex responses in the lower H-max
0.2 mV 20 ms
Figure 1 A printout showing H-max resulting from one of the adopted head positions. S, stimulus; M, direct muscle response (the M-wave). With increasing stimulus voltage, the amplitude of the H-wave declines, while the M-wave appreciates.
Eke-Okoro:
limbs. It can be said that there is interaction between the lumbar and cervical regions of the spinal cord in the static situation of H-reflex experiments, possibly through propriospinal neuron connection’. The reflex responses also show some side difference between the left and right legs. The H-max was augmented in right tibia1 nerve stimulation when compared to left tibia1 nerve stimulation for most of the head positions. This pattern may have resulted from a righting response related to the influence of tonic neck and labyrinthine reflexes2. It was expected that the significant influence of the head positions on reflex transmisssion in the lower limbs could have been seen in the gait situation. This means that the hypothesis of this study was supported only in the reflex experiment but not in gait. An explanation for this result may be that the static reflex experimental situation could not be effectively related to the dynamic gait situation. In a previous study it was shown that changes in arm position significantly affected gait parameters (EkeOkoro, unpublished data). The implication may be that the gait generators were directly stimulated, since they control the upper and lower limbs respectively6. Again, in a static situation changes in arm position have been shown to alter the pattern of reflex transmission in the lower limbs’. In the present experiments the effects of head position on gait (a dynamic action) may have been
Head position
and lower limb responses
111
resulting from any alteration in head position. Perhaps the postural displacement of the centre of mass of the body resulting from alterations in head position may have been compensated for proximally during arm swing, instead of distally during foot stride of gait. Further studies need to be done to explain this phenomenon. Acknowledgement This study was supported with Senate Research Grant (90/30) of the University of Nigeria.
References Delwaide PJ, Figiel C, Richelle C. Effects of postural changes in the upper limb on reflex transmission in the lower limbs. J Neurol Neurosurg Psychiatry 1977; 40: 616-21
Hayes KC, Sullivan J. Tonic neck reflex influences on tendon and Hoffman reflexes in man. Electromyogr Clin Neurophysiol
1976; 16: 251-61
eclipsed by neural factors activated during stride movements. Such neural factors would compensate for
Brown TG. The intrinsic factors in the act of propression in the mammal. Proc R Sot B 1911; 84: 308-19 Viala D, Vidal C. Evidence for distinct spinal locomotion generators supplying respectively fore- and hindlimbs in the rabbit. Brain Res 1978; 155: 182-6 Larsson LE, Odenrick P, Sandlund B, Weitz P, Oberg PA. The phases of the stride and their interaction in human gait. Stand J Rehabil Med 1980; 12: 107-12 Eke-Okoro ST. Functional dispositions of the spinal stepping generators and their half-centres. Electromyogr
even the smallest dislodgement
Clin Neurophysiol
of the centre of mass
1991; 31: 81-3
The 6th International Symposium of the Physical Medicine Research Foundation organized in association with
The Czech Society of Musculoskeletal Medicine Prague, Czechoslovakia 4-6 June 1993 The symposium will include invited lectures, free papers, and poster presentations, which will be augmented by an extensive satellite programme of clinical workshops and discussion groups. The main scientific sessions will be accompanied by a technical and pharmaceutical exhibition. For further information please contact the relevant secretariat: North American Secretariat Physical Medicine Research Foundation Suite 501, 207 West Hastings Street Vancouver, BC V6B 1H7 Canada
European Secretariat Czech Medical Society Sokolskrl 3 1 120 26 Praha 2 Czechoslovakia
Tel: +604 684 4148 Fax: +604 684 6247
Tel: +42 2 29 68 89 Fax: +42 2 235 24 12 or +42 2 29 46 10