Electroencephalography and Clinical Neurophysiology/Electromyography and Motor Control
Anticipatory postural adjustments in conditions of postural instability
Introduction
Anticipatory postural adjustments (APAs) can be seen in postural muscles prior to self-triggered or self-inflicted postural perturbations. Their assumed role is to counteract the expected mechanical effects of the perturbation in a feedforward manner (Bouisset and Zattara, 1990; Massion, 1992). The process of generation of APAs is likely to be affected by 3 major factors: (1) expected magnitude and direction of the perturbation; (2) voluntary action associated with the perturbation; and (3) postural task.
Effects of the first two factors, related to the forthcoming perturbation and to the motor action, have been studied relatively extensively. In particular, it has been shown that the intensity of APAs is graded as a function of the magnitude and direction of an expected postural perturbation (Horak et al., 1984; Dick et al., 1986; Lee et al., 1987; Bouisset and Zattara, 1990; Aruin and Latash, 1995a). Experiments with load manipulations let the experimenters separate the effects of the magnitude of motor action and of the magnitude of perturbation upon the APAs. Such studies have suggested that both the magnitude of the action and the magnitude of the perturbation can affect APAs independently (Dufosse et al., 1985; Paulignan et al., 1989; Aruin and Latash, 1995b, Aruin and Latash, 1996).
Reports on the dependence of APAs on the stability demands of the postural task have been somewhat conflicting, suggesting that the dependence may be non-monotonic. In particular, APAs associated with voluntary movements were attenuated or absent when the posture was unstable (Nouillot et al., 1992) as well as when it was very stable (Nardone and Schieppati, 1988). In experiments with backward bending, the anticipatory EMG burst in the calf muscles was reduced when the subjects performed the same task while standing on a small plate placed on a narrow support (Pedotti et al., 1989).
Based on these reports, we formulated the following hypothesis: Since, by their own nature, APAs can provide only an approximate compensation for an expected perturbation, the central nervous system (CNS) may consider them as additional potential sources of postural perturbation. Thus, in conditions of postural instability, the CNS may use an adaptive strategy in order not to subject the unstable equilibrium to additional, potentially perturbing forces. Such a strategy may lead to a reorganization of APAs which may include, in particular, an attenuation of APAs reflected in electromyographic and biomechanical characteristics, as well as other changes in the timing and level of activity in some postural muscles and shifts of the center of pressure. To test this hypothesis, we used an earlier paradigm (Aruin and Latash, 1995b) which includes releasing a standard load from the extended arms with a standard motor action. Within this paradigm, stability requirements were manipulated while both motor action and parameters of the perturbation remained unchanged.
Section snippets
Subjects
Thirteen subjects, 6 males and 7 females, mean age, 31.7 (±3.4 standard error) years, mean weight 77.5 (±6.2) kg, and mean height 1.73 (±4.2) m, took part in Expt. 1. Six subjects, 3 males and 3 females, mean age 31.8 (±1.6) years, mean weight 67.5 (±3.2) kg, and mean height 1.71 (±0.2) m, participated in Expt. 2. All the subjects were free of any known neurological or muscle disorders, or arthritis. They gave informed consent according to the procedures approved by the Compliance Committee of
Experiment 1
APAs could be seen as changes in the background activity (EMG) of postural muscles starting from about 100 to 150 ms prior to the perturbation (Fig. 2). Typical APA patterns included an anticipatory inhibition in the background activity of erector spinae, biceps femoris, and soleus muscles and an anticipatory increase in the activity of rectus abdominis, rectus femoris and tibialis anterior. Different subjects could demonstrate somewhat different patterns of anticipatory changes in the
Different effects of postural instability on the APAs in different muscles
Our experiments have demonstrated that the magnitude of APAs in conditions of a standard perturbation triggered by a standard motor action by the subject depends on two factors related to the postural task, namely, the plane of postural instability and the effective width of support. The last factor may be considered an inverse measure of the degree of instability. There were clear differences in the patterns of the dependencies of APAs in different postural muscles on the plane and degree of
Unlinked reference
Cited but not listed (please insert reference below or delete citation): Gottlieb et al., 1989.
Acknowledgements
This study was supported in part by Grant HD-37141 from the National Center for Medical Rehabilitation Research, NIH.
References (30)
- et al.
Anticipatory postural adjustments during self-initiated perturbations of different magnitude triggered by a standard motor action
Electroenceph. clin. Neurophysiol.
(1996) - et al.
Anticipatory postural adjustments associated with arm movements during balancing on unstable support surface
Int. J. Psychophysiol.
(1996) An assessment of stretch reflex function
Prog. Brain Res.
(1976)Movement, posture and equilibrium: Interaction and coordination
Prog. Neurobiol.
(1992)Postural control system
Curr. Opin. Neurobiol.
(1994)- et al.
Do fast voluntary movements necessitate anticipatory postural adjustments even if equilibrium is unstable?
Neurosci. Lett.
(1992) - et al.
A coactivation strategy in anticipatory postural adjustments in persons with Down syndrome
Motor Control
(1997) - Aruin, A.S. and Latash, M.L. Directional specificity of postural muscles in feed-forward postural reactions during fast...
- Aruin, A.S. and Latash, M.L. The role of motor action in anticipatory postural adjustments studied with self-induced...
- et al.
Anticipatory postural adjustments during predictable and self-inflicted perturbations in Down syndrome
Brazil Int. J. Adapt. Phys. Ed. Res.
(1994)
Anticipatory postural adjustments during standing in below-the-knee amputees
Clin. Biomech.
Postural adjustments associated with rapid voluntary arm movements in patients with Parkinson's disease
Adv. Neurol.
Associated postural adjustments in Parkinson's disease
J. Neurol. Neurosurg. Psychiat.
Postural forearm changes induced by predictable in time or voluntary triggered unloading in man
Exp. Brain Res.
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