Exp Brain Res (1992) 89:229-231
Experimental Brain Research 9 Springer-Verlag1992
Research Note
Regulation of bipedal stance: dependency on "load" receptors V. Dietz 1, A. Gollhofer 2, M. Kleiber 1, and M. TrippeP 1 Department of Clinical Neurology and Neurophysiology and 2 Institute of Sport Sciences, University of Freiburg, Hansastr. 9, W-7800 Freiburg, Federal Republic of Germany Received August 5, 1991 / Accepted January 7, 1992 Summary. According to recent observations, influence of body load has to be taken into account for the neuronal control of upright stance in addition to the systems known to be involved in this regulation (e.g. afferent input from vestibular canals, visual and muscle stretch receptors). The modulation of compensatory leg muscle electromyographic (EMG) responses observed during horizontal body posture indicates the existence of a receptor system which responds to loading of the body against the supporting platform. This receptor should be located within the extensor muscles because a compensatory EMG response and a loading effect on this response was only present following translational, but not rotational impulses. As the EMG responses were identical to those obtained during upright stance, it is argued that these load receptors activate postural reflexes. According to recent observations in the spinal cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait. Key words: Stance regulation - Compensatory E M G responses - Rotational/translational perturbations Load receptors - Postural reflexes - Human
Upright human stance and gait is an unstable equilibrium condition which requires a continuous neuronal regulation in order to hold the body's centre of mass over the support area of the feet. Afferent inputs from visual (Nashner and Berthoz 1978), vestibular (Allum and Pfaltz 1985) and stretch reflex (Diener et al. 1984; Dietz et al. 1987) systems are known to be involved in the control of stance and gait. However, as demonstrated during both space (Clement et al. 1984) and immersion (Dietz et al. 1989b) experiments these sensory systems cannot provide information about the influence of gravity upon upright stance. Afferent input from "gravityOffprint requests to: V. Dietz
dependent" receptors is required to indicate the projection of the body's centre of mass within the base of support. The localization and behaviour of load receptors which are suggested to provide this information are revealed in this study in which a new function is attributed to a well known receptor type, the Golgi tendon organs. Investigations on stance regulation have already indicated that the body's centre of gravity (CG) is the variable controlled by the central nervous system (Berger et al. 1984; Dietz et al. 1989b). The aim of this study was to define both the type and behaviour of the receptor that signals the projection of the centre body mass vector to the feet. For this purpose rotational and "translational" dorsiflexing displacements (6 degs) were randomly induced at the ankle joints under different loading conditions of the body. It was only during "translational" displacements that different torques were imposed by this loading upon the body which resulted in compensatory activation of the leg extensor muscles. This feature could be studied by placing the subjects' feet 25 cm above the axis of platform rotation thereby inducing a translational displacement component (approximately 3 cm; see schematic drawings in Fig. 1) while other biomechanical parameters (i.e. displacement velocity of the ankle joint and head acceleration) were within the same range as those seen during rotational displacements. These experiments were performed during upright stance and horizontal body position with informed consent of the subjects. During the latter condition, the subjects were pressed against the supporting surface by elastic bands which were fixed at the shoulders and on the moveable platform. By this approach the subjects could be loaded against the platform with 30, 60 and 100% of their body weight. The latter experiments were performed in order to 1) compare the surface EMG responses of the gastrocnemius and tibialis anterior muscles between the upright and horizontal condition, i.e. to estimate the influence of the vestibular system on the compensatory EMG responses and, 2) to investigate the influence of loading of the body on the response behaviour. The
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Fig. 1A, B. Mean of rectified and averaged (n = 10) leg muscle EMG responses together with the ankle joint position of 10 subjects following a dorsiflexing rotation of the platform co-linear with the ankle joint, and with the ankle joints 25 cm above the rotational axis during upright stance (A) and in a horizontal position of the body (B). In the latter condition, the subjects were pressed at the shoulders against the moveable platform by 30, 60 and 100% of their body weight using elastic bands connecting the shoulders with the platform. The schematic illustrations indicate the movements induced by the two impulse modalities (solid and interrupted lines)
general technique for recording muscle responses induced by displacement signals and for data analysis has been described elsewhere (Dietz et al. 1989a). Figure 1A shows the mean E M G responses in the leg muscles following rotational and "translation" perturbations during upright stance. The rotational impulses were followed by a small short-latency E M G response in the gastrocnemius muscle and a late tibialis anterior ac-
Fig. 2. Relationship between the mean values ( + / - S D ) of the integral of the polysynaptic gastrocnemius response (from t = 70 ms to 180 ms; see Fig. 2) and pressure (percent of body weight) applied at the shoulders in 10 subjects. Significant differencesare indicated: ** p
Experimental Brain Research 9 Springer-Verlag1992
Research Note
Regulation of bipedal stance: dependency on "load" receptors V. Dietz 1, A. Gollhofer 2, M. Kleiber 1, and M. TrippeP 1 Department of Clinical Neurology and Neurophysiology and 2 Institute of Sport Sciences, University of Freiburg, Hansastr. 9, W-7800 Freiburg, Federal Republic of Germany Received August 5, 1991 / Accepted January 7, 1992 Summary. According to recent observations, influence of body load has to be taken into account for the neuronal control of upright stance in addition to the systems known to be involved in this regulation (e.g. afferent input from vestibular canals, visual and muscle stretch receptors). The modulation of compensatory leg muscle electromyographic (EMG) responses observed during horizontal body posture indicates the existence of a receptor system which responds to loading of the body against the supporting platform. This receptor should be located within the extensor muscles because a compensatory EMG response and a loading effect on this response was only present following translational, but not rotational impulses. As the EMG responses were identical to those obtained during upright stance, it is argued that these load receptors activate postural reflexes. According to recent observations in the spinal cat, this afferent input probably arises from Golgi tendon organs and represents a newly discovered function of these receptors in the regulation of stance and gait. Key words: Stance regulation - Compensatory E M G responses - Rotational/translational perturbations Load receptors - Postural reflexes - Human
Upright human stance and gait is an unstable equilibrium condition which requires a continuous neuronal regulation in order to hold the body's centre of mass over the support area of the feet. Afferent inputs from visual (Nashner and Berthoz 1978), vestibular (Allum and Pfaltz 1985) and stretch reflex (Diener et al. 1984; Dietz et al. 1987) systems are known to be involved in the control of stance and gait. However, as demonstrated during both space (Clement et al. 1984) and immersion (Dietz et al. 1989b) experiments these sensory systems cannot provide information about the influence of gravity upon upright stance. Afferent input from "gravityOffprint requests to: V. Dietz
dependent" receptors is required to indicate the projection of the body's centre of mass within the base of support. The localization and behaviour of load receptors which are suggested to provide this information are revealed in this study in which a new function is attributed to a well known receptor type, the Golgi tendon organs. Investigations on stance regulation have already indicated that the body's centre of gravity (CG) is the variable controlled by the central nervous system (Berger et al. 1984; Dietz et al. 1989b). The aim of this study was to define both the type and behaviour of the receptor that signals the projection of the centre body mass vector to the feet. For this purpose rotational and "translational" dorsiflexing displacements (6 degs) were randomly induced at the ankle joints under different loading conditions of the body. It was only during "translational" displacements that different torques were imposed by this loading upon the body which resulted in compensatory activation of the leg extensor muscles. This feature could be studied by placing the subjects' feet 25 cm above the axis of platform rotation thereby inducing a translational displacement component (approximately 3 cm; see schematic drawings in Fig. 1) while other biomechanical parameters (i.e. displacement velocity of the ankle joint and head acceleration) were within the same range as those seen during rotational displacements. These experiments were performed during upright stance and horizontal body position with informed consent of the subjects. During the latter condition, the subjects were pressed against the supporting surface by elastic bands which were fixed at the shoulders and on the moveable platform. By this approach the subjects could be loaded against the platform with 30, 60 and 100% of their body weight. The latter experiments were performed in order to 1) compare the surface EMG responses of the gastrocnemius and tibialis anterior muscles between the upright and horizontal condition, i.e. to estimate the influence of the vestibular system on the compensatory EMG responses and, 2) to investigate the influence of loading of the body on the response behaviour. The
230
Ankle dorsiflexing Rotation
12
lronslotion
I
-~10 E8
~6 laJ
d4 N ~032 0
3'o 6'0
Loading (% of bodyweight}
:
1
05 mV
J i
Ankle jointposition I
,
!
i
,
9o
6ostr0cn. m.
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I
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;
,
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i
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,/
,
,l__J ~ v
I
',
',, " - ~ . | 10o
!
f0
', 100
:
200 ms
f0
:
100
i
200 ms
Fig. 1A, B. Mean of rectified and averaged (n = 10) leg muscle EMG responses together with the ankle joint position of 10 subjects following a dorsiflexing rotation of the platform co-linear with the ankle joint, and with the ankle joints 25 cm above the rotational axis during upright stance (A) and in a horizontal position of the body (B). In the latter condition, the subjects were pressed at the shoulders against the moveable platform by 30, 60 and 100% of their body weight using elastic bands connecting the shoulders with the platform. The schematic illustrations indicate the movements induced by the two impulse modalities (solid and interrupted lines)
general technique for recording muscle responses induced by displacement signals and for data analysis has been described elsewhere (Dietz et al. 1989a). Figure 1A shows the mean E M G responses in the leg muscles following rotational and "translation" perturbations during upright stance. The rotational impulses were followed by a small short-latency E M G response in the gastrocnemius muscle and a late tibialis anterior ac-
Fig. 2. Relationship between the mean values ( + / - S D ) of the integral of the polysynaptic gastrocnemius response (from t = 70 ms to 180 ms; see Fig. 2) and pressure (percent of body weight) applied at the shoulders in 10 subjects. Significant differencesare indicated: ** p
