Role Of Anticipatory Postural Adjustments Research Articles

The role of anticipatory postural adjustments in interlimb coordination of coupled arm movements in the parasagittal plane: III. Difference in the energy cost of postural actions during cyclic flexion–extension arm movements, ISO- and ANTI-directionally coupled

When oscillating the upper limbs together in the parasagittal plane, movements coordination is lower (i.e., variability of the interlimb relative phase is higher) in antidirectional (ANTI) than in isodirectional (ISO) coupling. In contrast, we previously observed that for arm movements in the horizontal plane, the coordination was worse in ISO than ANTI and the energetic cost of postural activities was higher in ISO. Having hypothesised that the higher postural cost was one factor responsible for the coordination deficit in horizontal ISO, we measured the oxygen uptake ([Formula: see text]) in parasagittal movements, expecting that in this case too, the postural cost is higher in the less-coordinated mode (ANTI). Breath-by-breath metabolic ([Formula: see text], [Formula: see text]) and cardiorespiratory (HR, [Formula: see text]) parameters were measured in seven participants, who performed cyclic flexions-extensions in the parasagittal plane with either one arm or both arms, in ISO or ANTI coupling and at 1.4, 2.2 and 2.6Hz. In each condition, the intermittent exercise (12s movement, 12s rest) lasted 264s. A force platform recorded the mechanical actions to the ground. The exercise metabolic cost ([Formula: see text]) was found to be significantly higher in parasagittal ANTI than ISO. The movement amplitude being equal in the two modes, the ANTI-ISO difference should be ascribed to postural activities. This would confirm that the less-coordinated coupling mode requires the higher postural effort in parasagittal movements too. When rising the movement frequency, [Formula: see text] increased and linearly correlated with the coordination loss. Comparison of parasagittal with horizontal movements showed that [Formula: see text] was lower in parasagittal ANTI than in horizontal ISO (the less-coordinated modes), while it was not different between parasagittal ISO and horizontal ANTI (the more-coordinated modes).

The role of anticipatory postural adjustments in interlimb coordination of coupled arm movements in the parasagittal plane: II. Postural activities and coupling coordination during cyclic flexion–extension arm movements, ISO- and ANTI-directionally coupled

When coupling cyclic adduction-abduction movements of the arms in the transverse (horizontal) plane, isodirectional (ISO) coupling is less stable than antidirectional (ANTI) coupling. We proposed that such deficiency stems from the disturbing action that anticipatory postural adjustments exert on ISO coupling. To ascertain if postural adjustments differentiate ISO versus ANTI coupling coordination in other types of cyclic arm movements, we examined flexion-extension oscillations in the parasagittal plane. Oscillations of the right arm alone elicited cyclic Postural Adjustments (PAs) in the left Anterior Deltoid and Posterior Deltoid, which replicated the excitation-inhibition pattern of the prime movers right Anterior Deltoid, right Posterior Deltoid. Cyclic PAs also developed symmetrically in Erector Spinae (RES and LES) and in phase opposition in Ischiocruralis (RIC and LIC), so as to discharge to the ground both an anteroposterior force, Fy, and a moment about the vertical axis, Tz. Oscillations of both arms in ISO coupling induced symmetric PAs in both ES and IC muscles, thus generating a large Fy but no Tz. In ANTI coupling, PAs in RES and LES remained symmetric but smaller in size, while PAs in RIC and LIC were large and opposite in phase, resulting in a large Tz and small Fy. Altogether, PAs would thus favour ISO and hamper ANTI parasagittal movements because (1) in the motor pathways to the prime movers of either arm, a convergence would occur between the voluntary commands and the commands for PAs linked to the movement of the other arm, the two commands having the same sign (excitatory or inhibitory) during ISO and an opposite sign during ANTI; (2) the postural effort of trunk and leg muscles would be higher for generating Tz in ANTI than Fy in ISO. These predictions fit with the finding that coupling stability was lower in ANTI than in ISO, i.e., opposite to horizontal movements. In conclusion, in both parasagittal and horizontal arm movements, the less coordinated coupling mode was the one constrained by postural adjustments through the two above mechanisms.

The role of anticipatory postural adjustments (APAs) in interlimb coordination of coupled arm movements in the parasagittal plane: I. APAs associated with fast discrete flexion and extension movements of one arm or of both arms ISO- and ANTI-directionally coupled

Coupling stability during cyclic arm movements in the horizontal (transverse) plane is lower in ISO- than in ANTI-directional coupling. We proposed that such impairment arises from the interference exerted in ISO by the anticipatory postural adjustments (APAs) linked to the primary movements. To evaluate if a link between coupling stability and postural adjustments also exist for arm movements with different postural requirements, we focused on arm(s) flexion-extension in the parasagittal plane and started by analysing the APAs distribution in arm, trunk and leg muscles. Fast flexion and extension of the right arm elicited APAs in the left anterior and posterior deltoid that replicated the excitation-inhibition of the homologous prime movers; this pattern would favour ISO and contrast ANTI-coupled movements. Instead, in the left latissimus dorsi, APAs were opposite to the voluntary actions in the right latissimus dorsi, thus favouring ANTI coupling. Symmetrical APAs were also elicited in right and left erector spinae (RES, LES) and asymmetrical APAs in Ischiocruralis (RIC, LIC), while an antero-posterior force (Fy) and a moment about the vertical axis (Tz) were discharged to the ground. When fast discrete movements were ISO-coupled, APAs were symmetrical in trunk (RES, LES) and leg (RIC, LIC) muscles and a large Fy but no Tz was generated. In ANTI coupling, APAs in RES and LES remained symmetrical, whereas they became antisymmetrical in RIC and LIC. A large Tz and a small Fy were recorded. In conclusion, during parasagittal movements, APAs in are elicited in both ISO and ANTI coupling, at variance with horizontal movements where they are only present in ISO. This would suggest that the difference in coupling stability between the two modes is smaller (or even reversed) in parasagittal with respect to horizontal arm movements.

Compensatory but not anticipatory adjustments are altered in older adults during lateral postural perturbations

ObjectiveThis study investigated anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs) and their relationship in older adults during lateral postural perturbations. MethodsUnpredictable and predictable postural disturbances were induced by a swinging pendulum that impacted at the shoulder level of two groups of older adults, non-fallers (20) and fallers (20), and in a group of young control subjects (20). The electromyographic (EMG) activity of the postural muscles and the center of pressure (COP) displacement were recorded and quantified within the time intervals typical for APAs and CPAs. ResultsBoth groups of older adults (non-fallers and fallers) showed higher magnitude of EMG activity in the lateral muscles and increased COP displacement, particularly, during the CPAs time interval when compared to the young group. Older adults, however, were able to change the electrical activity of the muscles during the predictable task by generating APAs with similar magnitudes of those found in young subjects. ConclusionsCompensatory but not anticipatory adjustments are altered in older adults during predictable lateral postural perturbations.Significance: These findings provide new data on the role of APAs and CPAs in their relationship in older adults during external lateral perturbations and may advance current rehabilitative management strategies to improve balance control in older individuals.

Postural Adjustments in Catching: On the Interplay Between Segment Stabilization and Equilibrium Control

The purpose of this study was to investigate postural adjustments in one-handed ball catching. Specifically, the functional role of anticipatory postural adjustments (APA) during the initial arm raising and subsequent postural adjustments (SPA) for equilibrium control and ball-hand impact were scrutinized. Full-body kinematics and kinetics allowed an analysis of the mechanical consequences of raising up the arm and preparing for ball-hand impact. APA for catching were suggested to be for segment stabilization. SPA had a functional role for equilibrium control by an inverted pendulum mechanism but were also involved in preparing for the impact of the ball on the hand, which was illustrated by an increased postural response at the end of the movement. These results were compared with raising up the arm in a well-studied reaction-time task, for which an additional counter rotation equilibrium mechanism was observed. Together, our findings demonstrate that postural adjustments should be investigated in relation to their specific functional task constraints, rather than generalizing the functional role of these postural adjustments over different tasks.

The role of anticipatory postural adjustments in compensatory control of posture: 2. Biomechanical analysis

The central nervous system (CNS) utilizes anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain equilibrium while standing. It is known that these postural adjustments involve displacements of the center of mass (COM) and center of pressure (COP). The purpose of the study was to investigate the relationship between APAs and CPAs from a kinetic and kinematic perspective. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level while standing. Kinematic and kinetic data were recorded and analyzed during the time duration typical for anticipatory and compensatory postural adjustments. When the perturbations were unpredictable, the COM and COP displacements were larger compared to predictable conditions with APAs. Thus, the peak of COM displacement, after the pendulum impact, in the posterior direction reached 28 ± 9.6 mm in the unpredictable conditions with no APAs whereas it was 1.6 times smaller, reaching 17 ± 5.5 mm during predictable perturbations. Similarly, after the impact, the peak of COP displacement in the posterior direction was 60 ± 14 mm for unpredictable conditions and 28 ± 3.6 mm for predictable conditions. Finally, the times of the peak COM and COP displacements were similar in the predictable and unpredictable conditions. This outcome provides additional knowledge about how body balance is controlled in presence and in absence of information about the forthcoming perturbation. Moreover, it suggests that control of posture could be enhanced by better utilization of APAs and such an approach could be considered as a valuable modality in the rehabilitation of individuals with balance impairment.

The role of anticipatory postural adjustments in compensatory control of posture: 1. Electromyographic analysis

Anticipatory (APAs) and compensatory (CPAs) postural adjustments are the two principal mechanisms that the central nervous system uses to maintain equilibrium while standing. We studied the role of APAs in compensatory postural adjustments. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level, while standing with eyes open and closed. Electrical activity of leg and trunk muscles was recorded and analyzed during four epochs representing the time duration typical for anticipatory and compensatory postural control. No anticipatory activity of the trunk and leg muscles was seen in the case of unpredictable perturbations; instead, significant compensatory activation of muscles was observed. When the perturbations were predictable, strong anticipatory activation was seen in all the muscles: such APAs were associated with significantly smaller compensatory activity of muscles and COP displacements after the perturbations. The outcome of the study highlights the importance of APAs in control of posture and points out the existence of a relationship between the anticipatory and the compensatory components of postural control. It also suggests a possibility to enhance balance control by improving the APAs responses during external perturbations.

Vertical torque allows recording of anticipatory postural adjustments associated with slow, arm-raising movements

When performed in the upright position, voluntary arm-raising movements perturb balance. The maintenance of equilibrium requires postural adjustments, some of which can be anticipatory. It is usually suggested that the role of anticipatory postural adjustments is to stabilise the whole body centre of mass. During movements performed at low velocity (i.e. with a lower inertial perturbation), anticipatory postural adjustments have not systematically been detected by classical recording methods (mainly electromyography). The aim of this study was to use vertical torque to characterise anticipatory postural adjustments in slow movement and to determine the significance of this biomechanical parameter. Twenty healthy subjects performed self-paced, right arm-raising movements at low and high velocities. Movements were recorded by an optoelectronic system enabling the synchronization of video, force plate and electromyographic data. The force platform provided information on vertical torque and centre of foot pressure anteroposterior displacement. Electromyography activity was recorded from the right anterior deltoid and the bilateral biceps femoris, tibialis anterior and soleus muscles. Rapid, voluntary, unilateral movements were associated with an early centre of pressure backward shift, anticipatory vertical torque and electromyographic activities. In slow movements, only the anticipatory changes in vertical torque were consistently observed, with the same latency as in rapid movement. The existence of vertical torque in slow movement (when stabilisation of the centre of mass is not necessary) shows that this parameter does not serve to minimise the centre of mass displacement but rather contributes to the generation of arm movement.

Postural Perturbation by Electric Stimulation has no Effect upon Anticipatory Postural Adjustment

0079 Anticipatory postural adjustments (APA) have been known to assist equilibrium maintenance in standing humans by adjusting muscle activation prior to a postural perturbation. Previous studies have focused primarily on APA accompanying the relocation of the center of mass (COM). However, few studies are available which examine the effect of APA on quiet standing during an expected postural perturbation. PURPOSE: To investigate whether APA's are utilized during quiet standing when a subject encounters a postural perturbation. METHODS: Subjects stood quietly on force platform and center of pressure recordings and EMG activity was monitored during each 20–30 second trial. Electrical stimulation was applied to either the peroneal (PNS) or tibial (TNS) nerve bilaterally in order to produce a postural perturbation. College-age subjects (N = 8, 5 males and 3 females) were examined under three conditions: PNS, TNS, and no stimulation (NS). Each condition was tested under a vision and a no-vision condition. Eight trials were recorded for each of the six conditions. In each condition, subjects were able to anticipate the type of perturbation. The perturbation was randomly delivered during the 20–30 second trial, but subjects were aware of which stimulus condition was being presented. Sway parameters and EMG activity (sample rate = 1 kHz) from the pre-perturbation phase were analyzed. RESULTS: No differences were observed between the no-vision and the vision conditions, and data were pooled. Lateral deviation (1.27±0.68 in PNS, 1.35±0.64 in NS, and 1.37±0.69 in TNS, mm), and sagital deviation (2.86±1.42 in PNS, 3.04±1.46 in NS, and 2.86±1.41 in TNS, mm), sway velocity (6.97±2.70 in PNS, 7.13±2.76 in NS, and 7.15±2.44 in TNS, mm/sec), sway area (128.98±121.91 in PNS, 124.60±106.10 in NS, and 138.08±99.72 in TNS, mm2), sway amplitude (2.98±1.37 in PNS, 2.94±1.35 in NS, and 3.23±1.39 in TNS, mm), and background EMG of the tibialis anterior muscle (7.03±2.60 in PNS, 8.61±5.46 in NS, and 6.72±1.84 in TNS) and the soleus muscle (22.92±13.12 in PNS, 25.51±14.86 in NS, and 26.11±14.77 in TNS) showed no significant difference among stimulation types. CONCLUSIONS: Perturbation via electrical stimulation which produces an anterior/posterior displacement of the body is not accompanied by anticipatory changes in subject behavior. The role of APA with elderly subjects and/or populations with balance deficits remains to be determined.

The role of anticipatory postural adjustments in a rocking on heels movement

We studied the anticipatory postural adjustments (APAs) associated with a voluntary rocking on heels movement performed in a self-paced manner. Ground reaction forces and the EMG activity of the leg muscles were recorded. Such a movement shifted the centre of gravity (CG) backwards, due to APAs on the lower limbs. It is generally assumed that APAs only generate corrections in the opposite direction to the perturbation due to the focal movement. However, our study shows that APAs, by creating the initial backward oriented impulse, displace the CG backwards and generate the dynamic conditions required to move.

Anticipatory postural adjustments associated with rotational perturbations while standing on fixed and free-rotating supports.

The role of anticipatory postural adjustments (APAs) has been commonly hypothesized to stabilize the body's center of mass (COM) from reaction forces and torques induced by voluntary movements in a feed-forward manner. This hypothesis was developed from studies which investigated movements that induced anterior-posterior or medial-lateral perturbation to body posture. However, the role of APAs in tasks that induce perturbations about the vertical axis, which are associated with minimal COM displacements, is unclear. The purpose of this study was to examine APAs associated with upper arm movements that induce perturbation about the body's vertical axis. Eight healthy subjects performed bilateral or unilateral shoulder movements in the sagittal or frontal plane that induced rotational perturbation about the body's vertical axis, while standing on a support which was either fixed or free to rotate about the body's vertical axis. Changes in the background activity of trunk and leg muscles on both sides of the body, as well as reaction moment about the vertical axis were quantified within the time interval typical of APAs. On the fixed support, clear asymmetry between right and left muscle activity was observed in biceps femoris and soleus during APAs across all tasks. These asymmetries were specific to the movement direction. When the same tasks were performed on a free-rotating support, the asymmetry that was observed on fixed support decreased. We suggest that the CNS uses asymmetric activity of right and left muscles during APAs to rotate the body segments in the direction opposite to the perturbation. When ground reaction moments did not aid in counteracting the forthcoming perturbation while standing on a free-rotating support, the asymmetric muscle activity decreased to minimize further inter-segmental rotations.

The role of anticipatory postural adjustments during whole body forward reaching movements

The purpose of this study was to examine the role of anticipatory postural adjustments (APAs) in the execution of forward oriented whole body reaching movements. From the standing position, eight healthy subjects were asked to reach an object placed at 45 cm from the feet, at both naturally paced and fast speeds. Electromyographic signals of six antagonistic muscles were analysed in conjunction with centre of mass (CM) displacements, centre of foot pressure displacements and resultant ground reaction forces. Results revealed that APAs created necessary angular momentum of body segments for effective task execution. These results suggest that APAs can initiate movements conducted from a fixed base of support, and in this context do not act solely to stabilize the CM.

The role of anticipatory postural adjustments and gravity in gait initiation.

This study analyzes the anticipatory postural adjustments which precede heel-off by considering the participation of the gravitational and muscular actions about the ankle joints during the gait initiation process. The resultant moment about the ankle joints and the gravitational moment were calculated using a biomechanical model in five normal subjects for three different speed conditions. The results show that the variations of these two moments are correlated to the velocity at the end of the first step. Nevertheless, a significant variation of the ankle joints moment occurs at the beginning of the anticipatory phase, whereas the gravity effect is still insignificant. These findings show how the successive controls of the muscular actions acting during the anticipatory movement and of the gravity action acting principally during the step execution allow the subject to reach the velocity which has been initially and centrally decided, by the end of the first step.