Three components of postural control associated with pushing in symmetrical and asymmetrical stance

A number of occupational and leisure activities that involve pushing are performed in symmetrical or asymmetrical stance. The goal of this study was to investigate early postural adjustments (EPAs), anticipatory postural adjustments (APAs), and compensatory postural adjustments (CPAs) during pushing performed while standing. Ten healthy volunteers stood in symmetrical stance (with feet parallel) or in asymmetrical stance (staggered stance with one foot forward) and were instructed to use both hands to push forward the handle of a pendulum attached to the ceiling. Bilateral EMG activity of the trunk and leg muscles and the center of pressure (COP) displacements in the anterior–posterior (AP) and medial–lateral (ML) directions were recorded and analyzed during the EPAs, APAs, and CPAs. The EMG activity and the COP displacement were different between the symmetrical and asymmetrical stance conditions. The COP displacements in the ML direction were significantly larger in staggered stance than in symmetrical stance. In staggered stance, the EPAs and APAs in the thigh muscles of the backward leg were significantly larger, and the CPAs were smaller than in the forward leg. There was no difference in the EMG activity of the trunk muscles between the stance conditions. The study outcome confirmed the existence of the three components of postural control (EPAs, APAs, and CPAs) in pushing. Moreover, standing asymmetrically was associated with asymmetrical patterns of EMG activity in the lower extremities reflecting the stance-related postural control during pushing. The study outcome provides a basis for studying postural control during other daily activities involving pushing.     

Anticipatory postural adjustments and the latency of compensatory stepping reactions in humans

A compensatory stepping response is a commonly used strategy in recovering balance control after a postural perturbation. Unlike gait initiation, the compensatory stepping often occurs without an anticipatory postural adjustment (APA), in which body weight is shifted to the swing leg first and then back to the stance leg prior to foot lifting. In postural perturbation studies using a moving platforms stepping responses without an APA were found to have shorter latency to foot lifting than trials with an APA. We studied stepping responses of healthy young adults under postural perturbation of a pulling force impulse on the subject's waist. In contrast to previous studies, the latency of foot lifting was found in the current study to be shorter in the trials with an APA than trials without an APA. Furthermore, greater amplitude of an APA was associated with a shorter latency of foot lifting. Response with an APA of large amplitude may indicate high level of determinant for foot lifting. A pause as to whether or not to initiate/complete a stepping response is suggested to be partially the cause of delayed foot lifting in trials without an APA or with small amplitude of the APA.     

Asymmetry of recurrent dynamics as a function of postural stance

This experiment was setup to investigate the deterministic and stochastic properties of the recurrent dynamics of the center of pressure trajectories of each leg (COP_left and COP_right) and whole-body (COP_net) as a function of different foot positions in postural stance (side-by-side, staggered, and tandem standing) and the availability of visual information. The foot position of postural stance can induce degrees of asymmetry of postural instabilities as well as load on each leg that it was hypothesized would influence the deterministic and stochastic properties of COP fluctuations of each leg and of COP_net. Young adults performed two 60?s trials of quiet standing at each posture–vision condition. The availability of visual information increased COP path length, but had no effect on the recurrent dynamics of COP trajectories. Recurrence quantification analysis showed that recurrence, determinism, and entropy were dependent on the direction (AP/ML) of COP motion and foot position during postural stances. The degree of asymmetry between the left and right leg COP dynamics differed across all postural stances and COP_net dynamics were more similar to those of the more loaded leg. The cross-recurrence quantification analysis also revealed asymmetries in the coordination coupling of AP/ML under each leg; although, these differences were markedly reduced in tandem postures. The findings support the postulation that the asymmetry generated through mechanical constraints (foot position and load) is related to asymmetrical recurrent dynamics of the individual leg and COP_net based on the degree of postural instability.     

Reversals of anticipatory postural adjustments during voluntary sway in humans

We describe reversals of anticipatory postural adjustments (APAs) with the phase of a voluntary cyclic whole-body sway movement. Subjects ( n = 9) held a standard load in extended arms and released it by a bilateral shoulder abduction motion in a self-paced manner at different phases of the sway. The load release task was also performed during quiet stance in three positions: in the middle of the sway range and close to its extreme forward and backward positions. Larger APAs were seen during the sway task as compared to quiet stance. Although the direction of postural perturbation associated with the load release was always the same, the direction of the APAs in the leg muscles reversed when the subjects were close to the extreme forward position as compared to the APAs in other phases and during quiet stance. The trunk muscles showed smaller APA modulation at the extreme positions but larger modulation when passing through the middle position, depending on the direction of sway, forward or backward. The phenomenon of APA reversals emphasizes the important role of safety in the generation of postural adjustments associated with voluntary movements. Based on these findings, APAs could be defined as changes in the activity of postural muscles associated with a predictable perturbation that act to provide maximal safety of the postural task component.     

Effect of lower limb muscle fatigue on anticipatory postural adjustments associated with bilateral-forward reach in the unipedal dominant and non-dominant stance

Voluntary arm movements are preceded by dynamical and electromyographical (EMG) phenomena in “postural segments” (i.e. body segments not directly involved in the voluntary movement) called “anticipatory postural adjustments” (APA). The present study examined how the central nervous system organizes APA under fatigued state of postural musculature elicited by series of high-level isometric contractions (HIC), i.e. corresponding to 60% of maximal voluntary contraction. Subjects (N = 14) purposely performed series of bilateral-forward reach task (BFR) under unipodal stance (dominant and non-dominant) before (“no fatigue” condition, NF) and after (“fatigue” condition, F) a procedure designed to obtain major fatigue in hamstrings. Centre-of-gravity acceleration, centre-of-pressure displacement, and electrical activity of trunk and leg muscles were recorded and quantified within a time-window typical of APA. Results showed that there was no significant effect of fatigue on the level of muscle excitation and APA onset in any of the postural muscles recorded. Similarly, no change in APA onset could be detected from the biomechanical traces. In contrast, results showed that the amplitude of anticipatory centre-of-pressure displacement and centre-of-gravity acceleration reached lower value in F than in NF. Similar results were obtained whether dominant or non-dominant leg was considered. The changes in biomechanical APA features could not be ascribed to a different focal movement performance (maximal BFR velocity and acceleration) between F and NF. These results suggest that, when fatigue is induced by HIC, the capacity of the central nervous system to adapt APA programming to the fatigued state of the postural muscle system might be altered.     

Do anticipatory postural adjustments occurring in different segments of the postural chain follow the same organisational rule for different task movement velocities, independently of the inertial load value?

Dynamic phenomena, termed anticipatory postural adjustments (APA), are known to precede the onset of voluntary movement. Their anticipatory nature confers a particular status on APAs: as they cannot be triggered reflexly by afferent signals induced by a voluntary movement, it can be asked whether the APA parameters are centrally programmed as a function of some task movement parameters or are only the peripheral consequence of control variables. To this end the present study aims to determine whether the APAs occurring at the different sites of the postural chain yield the same accelerometric patterns and follow the same organisational rules when the task movement velocity changes, independently of the inertial load value. Subjects performed unilateral shoulder flexions at maximal and submaximal velocities, with (IUF) and without (OUF) an additional inertial load. Accelerometers were attached to the wrist and trunk, and on both sides of the body at shank, thigh, hip and shoulder. The results show that: 1) there was evidence of anticipatory acceleration in all segments of the postural chain; 2) each acceleration profile for the anticipatory phase was maintained over different focal movement velocities whether there was an additional load or not; 3) there were significant linear relationships between the amplitude of each segmental anticipatory acceleration and the square of the task movement velocity, the slope of which differs as a function of the inertial load; 4) there were close intersegmental correlations between these anticipatory accelerations which did not depend on the inertial load. In addition the correlation between the lower limbs and the opposite side of the body was positive, suggesting a diagonal postural pattern. A comparison of the present kinematic data with the corresponding EMG data reported in the literature argues in favour of a centrally determined kinematic pattern. It is proposed that the diagonal postural pattern between postural segments be considered as one of the order rules which could simplify the control process of asymmetrical movement. The anticipatory kinematics of each of the body segments would be calibrated with the velocity and the inertial load and scaled to the other segments to counteract the perturbing effect of the asymmetrical focal movement on body balance.     

Perturbations of ground support alter posture and locomotion coupling during step initiation in Parkinson��s disease

During the initiation of stepping, anticipatory postural adjustments (APAs) for lateral weight transfer and propulsion normally precede the onset of locomotion. In Parkinson's disease (PD), impaired step initiation typically involves altered APA ground force production with delayed step onset and deficits in stepping performance. If, as in stance and gait, sensory information about lower limb load is important for the control of stepping, then perturbations influencing loading conditions could affect the step initiation process. This study investigated the influence of changes in lower limb loading during step initiation in patients with PD and healthy control subjects. Participants performed rapid self-triggered step initiation with the impending single stance limb positioned over a pneumatically actuated platform. In perturbation trials, the stance limb ground support surface was either moved vertically downward (DROP) or upward (ELEVATE) by 1.5 cm shortly after the onset of the APA phase. Overall, PD patients demonstrated a longer APA duration, longer time to first step onset, and slower step speed than controls. In both groups, the DROP perturbation reinforced the intended APA kinetic changes for lateral weight transfer and resulted in a significant reduction in APA duration, increase in peak amplitude, and earlier time to first step onset compared with other conditions. During ELEVATE trials that opposed the intended weight transfer forces both groups rapidly adapted their stepping to preserve standing stability by decreasing step length and duration, and increasing step height and foot placement laterally. The findings suggested that sensory information associated with limb load and/or foot pressure modulates the spatial and temporal parameters of posture and locomotion components of step initiation in interaction with a centrally generated feedforward mode of neural control. Moreover, impaired step initiation in PD may at least acutely be enhanced by augmenting the coupling between posture and locomotion.     

Grip force control during gait initiation with a hand-held object

When walking with a hand-held object, grip force is coupled in an anticipatory manner to changes in inertial force resulting from the accelerations and decelerations of gait. However, it is not known how grip and inertial forces are organized at the onset of gait, and if the two forces are coupled in the early phases of gait initiation. Moreover, initiating walking with an object involves the coordination of anticipatory postural (e.g., ground reaction force changes) and grasping adjustments. The aim of this study was to investigate the relationship of ground reaction, grip, and inertial force onsets, and the subsequent development of the coupling of grip and inertial forces during gait initiation with a hand-held object. Ten subjects performed gait initiation with a hand-held object following predictable and unpredictable start signals. We found that ground reaction and grip force onsets were closely linked in time regardless of the predictability of the start signal. In the early period of gait initiation, the grip force started to increase prior to inertial force changes. While the strength of the coupling of grip and inertial forces was moderate in this early phase, it increased to values observed during steady-state gait after the swing foot left the ground. The early grip force increase and the coupling of grip and inertial forces represent an anticipatory control process. This process establishes an appropriate grip-inertial force ratio to ensure object stability during acceleration after foot-off and maintains this increased ratio thereafter. The results suggest that grasping and whole body movements are governed by a common internal representation.     

Changes in the force-sharing pattern induced by modifications of visual feedback during force production by a set of fingers

The aim of this work was to propose developmental indexes relative to the control of balance and gravity forces, using force-plate data, for children in their first 5 years of independent walking. The first part of this paper is devoted to the definition of an index to quantify postural capacity during walking. Based on the assumption that the vertical acceleration of center of mass (CM) reflects the capacity of muscular forces between the head-arms-trunk and the stance leg segments to control the external forces, the value of the CM vertical acceleration at foot contact is proposed as a developmental index of the postural capacity of the child to control gravitational forces. This index was analyzed longitudinally in five children, over the course of eight experimental sessions. The children were examined during their first 5 years of independent walking (for a total of 457 step sequences). The covariation between the CM vertical acceleration at foot contact and the gait velocity was considered as a second index characterizing the development of coordination between the postural and dynamic requirements of body progression. From these indexes it was established that the postural capacity needed just to control balance with the leg muscles was not attained before 4–5 years of independent walking, i.e., at about 5–6 years of age. Received: 2 June 1997 / Accepted: 22 December 1997     

Altered gene expression in cultured microglia in response to simulated blast overpressure: possible role of pulse duration

This study was set-up to investigate the effect of mechanical constraints arising from different postural stances on the AP and ML pattern of the time evolutionary properties of phase synchronization of the foot dynamics, together with their relation to the dynamics of COP_NET. The results showed that postural stance differentially influenced the phase synchronization (number and duration of the epochs) between the individual feet COPs and of each foot to the COP_NET. The side-by-side stance had longer phase synchronization duration in the anterior-posterior (AP) direction and shorter duration in the medial-lateral (ML) direction than the staggered and tandem postures. In the staggered and tandem postures, the relative phase between the rear foot COP and the COP_NET had longer phase synchronization than the relative phase between the COPs of the two feet and that between the front foot COP and the COP_NET. The time evolutionary properties of the feet coupling dynamics revealed patterns of “stable” but “flexible” control of the postural system as a function of the asymmetrical foot loading in the stance.     

Modulation of proprioceptive inflow when initiating a step influences postural adjustments

A synergistic inclination of the whole body towards the supporting leg is required when producing a stepping movement. It serves to shift the centre of mass towards the stance foot. While the importance of sensory information in the setting of this postural adjustment is undisputed, it is currently unknown the extent to which proprioceptive afferences (Ia) give rise to postural regulation during stepping movement when the availability of other sensory information relying on static linear acceleration (gravity) is no longer sensed in microgravity. We tested this possibility asking subjects to step forward with their eyes closed in normo- and microgravity environments. At the onset of the stepping movement, we vibrated the ankle muscles acting in the lateral direction to induce modification of the afferent inflow (Ia fibres). Vibration-evoked movement (perceived movement) was in the same direction as the forthcoming body shift towards the supporting side (current movement). A control condition was performed without vibration. In both environments, when vibration was applied, the hip shift towards the supporting side decreased. These postural modifications occurred, however, earlier in normogravity before initiating the stepping movement than in microgravity (i.e. during the completion of the stepping movement). Our results suggest that proprioceptive information induced by vibration and afferent inflow related to body movement exaggerated sense of movement. This biased perception led to the postural adjustment decrease. We propose that in both environments, proprioceptive inflow enables the subject to scale the postural adjustments, provided that body motion-induced afferences are present to activate this postural control.     

Asymmetric balance control between legs for quiet but not for perturbed stance

Interlateral performance asymmetry in upright balance control was evaluated in this investigation by comparing unipedal stance on the right versus the left leg. Participants were healthy young adults, hand–foot congruent preference for the right body side. Balance performance was evaluated in unperturbed quiet stance and in the recovery of balance stability following a mechanical perturbation induced by unexpected load release. Evaluation was made under availability of full sensory information, and under deprivation of vision combined with distortion of sensory inputs from the feet soles. Results from perturbed posture revealed that muscular response latency and postural sway were symmetric between the legs. Unipedal stance was more stable when the body was supported on the right as compared with the left leg. No interaction was found between leg and sensory condition. Our findings are interpreted as resulting from specialization of the sensorimotor system controlling the right leg for continuous low-magnitude postural adjustments, while corrections to large-scale stance sway are symmetrically controlled between body sides.     

Environmental constraints on foot trajectory reveal the capacity for modulation of anticipatory postural adjustments during rapid triggered stepping reactions

This study used environmental restrictions on foot movement to challenge the capacity of the central nervous system (CNS) to counter the lateral instability that arises after foot-lift during rapid triggered stepping reactions evoked by unpredictable postural perturbation. The objective was to determine the extent to which lateral stability could be regulated via modulation of the mediolateral (m-l) anticipatory postural adjustment (APA) that precedes foot-lift. A high frontal obstacle was used to double the required swing duration, and thereby increase the potential for the center of mass (COM) to fall laterally toward the unsupported side, during forward-step reactions. The capacity to use lateral step placement to recover lateral stability was restricted by means of lateral barriers. Six healthy young adults were tested. In obstacle-only trials, the APA was insufficient to prevent increased lateral COM motion during the prolonged swing phase; hence, lateral step placement was necessitated. However, when lateral stepping was obstructed, the CNS was able to upregulate the APA amplitude so as to prevent this increase in lateral COM motion. The swing foot was placed medially, with no detriment to clearing the frontal obstacle or recovering equilibrium. There was no change in step timing or anteroposterior (a-p) COM motion. While previous studies have suggested that the a-p COM progression may determine the extent to which the m-l APA is expressed or truncated during triggered stepping reactions evoked by unpredictable perturbation, the present findings demonstrate that prior knowledge of environmental demands can lead to predictive efforts to modulate the APA during such reactions. An apparent preference to underscale anticipatory efforts when lateral step placement is permitted suggests that the CNS may be acting to avoid some potential risk or cost associated with the execution of a large APA.     

Stability limits modulate whole-body motor learning

Our daily movements exert forces upon the environment and also upon our own bodies. To control for these forces, movements performed while standing are usually preceded by anticipatory postural adjustments (APAs). This strategy is effective at compensating for an expected perturbation, as it reduces the need to compensate for the perturbation in a reactive manner. However, it can also be risky if one anticipates the incorrect perturbation, which could result in movements outside stability limits and a loss of balance. Here, we examine whether the margin for error defined by these stability limits affects the amount of anticipation. Specifically, will one rely more on anticipation when the margin for error is lower? Will the degree of anticipation scale with the margin for error? We took advantage of the asymmetric stability limits (and margins for error) present in the sagittal plane during upright stance and investigated the effect of perturbation direction on the magnitude of APAs. We also compared anticipatory postural control with the anticipatory control observed at the arm. Standing subjects made reaching movements to multiple targets while grasping the handle of a robot arm. They experienced forward or backward perturbing forces depending on the target direction. Subjects learned to anticipate the forces and generated APAs. Although subjects had the biomechanical capacity to adapt similarly in the forward and backward directions, APAs were reduced significantly in the backward direction, which had smaller stability limits and a smaller margin for error. Interestingly, anticipatory control produced at the arm, where stability limits are not as relevant, was not affected by perturbation direction. These results suggest that stability limits modulate anticipatory control, and reduced stability limits lead to a reduction in anticipatory postural control.     

Why anticipatory postural adjustments in gait initiation need to be modified when stepping up onto a new level?

The study examined why anticipatory postural adjustments (APA) associated to gait initiation in a stepping up to a new level situation (SU) are reduced as compared to a level walking situation (LW), as previously reported. Five young adults performed gait initiation in both situations at normal and fast speed. Data from a force platform provided gait parameters related to the motion of the body's centre of mass (CM) on the anteroposterior (progression) and vertical axes. The electromyographic activity of the soleus of the stance limb (SOst) and the vastus lateralis of the swing limb (VLsw) were analyzed prior to and after the onset of the double stance phase. The results showed that APA and progression CM velocity at the time of foot contact were smaller in SU, whereas the peak of this velocity was similar in both situations. Thus, the change in progression velocity during the double stance phase had to be greater in SU than in LW. In both velocity conditions, the activity of SOst stopped after the time of foot contact in both situations, but clearly later in SU. So, this ankle plantar flexor muscle would be involved not only in the change of body lift but also in forward CM progression. The latter role of this muscle brought supporting evidence for the reduction of APA in SU, enabling the peak of progression velocity to be similar in both situations. Only in SU, the timing of activation of VLsw and deactivation of SOst strongly co-varied, showing the implementation of a motor synergy to fulfil the new requirements of the task, i.e. body lift.     

The strategies to regulate and to modulate the propulsive forces during gait initiation in lower limb amputees

We used the framework of motor program adaptability to examine how unilateral above-knee (AK) or below-knee (BK) amputee subjects organize the global and local biomechanical processes of generation of the propulsive forces during gait initiation to overcome the segmental and neuro-muscular asymmetry. The organization of the global biomechanical process refers to the kinematics behavior of the couple center of foot pressure (CoP) and center of mass (CoM); the organization of the local biomechanical process refers to the propulsive forces generated by the prosthetic or intact limb during the anticipatory postural adjustment phase and the step execution phase. Specifically, we examined: i) the strategy to regulate the progression velocity, i.e., to maintain it comparably when the leading limb changed from the prosthetic limb to the intact limb; and ii) the strategy to modulate the progression velocity, i.e., to increase it when gait was initiated with the prosthetic limb vs. intact limb. The kinematics of the CoM and CoP in the amputees showed the same global biomechanical organization that is typically observed in able-bodied subjects, i.e., the production of the forward disequilibrium torque was obtained by a backward shift of the CoP, followed by a forward acceleration of the CoM. However, gait initiation was achieved by using a different local strategy depending on which limb was used to initiate the step. For the regulation of the CoM progression velocity, when the gait was initiated with the intact limb, the slope of the progression velocity during the anticipatory postural adjustment phase (APA) was steeper and lasted longer, the step execution duration was shorter, and the variation of the CoM speed was lower. In other words, to regulate the speed of progression, the amputee subjects controlled the spatial and temporal parameters of the propulsive forces. In the modulation of the CoM progression velocity, when the gait was initiated with the intact limb, the amputees controlled only the intensity of the propulsive forces during both the APA and step execution phases. In contrast, when the gait was initiated with the prosthetic limb, the modulation resulted mainly from the propulsive forces generated during the step execution phase. These different strategies are discussed in terms of the subjects capacity to adapt the motor program for gait initiation to new constraints.An erratum to this article can be found at     

Dynamic transitions in stance support accompanying leg flexion movements in man

Summary The control processes underlying dynamic transitions in stance support during single leg flexion movements were investigated in human subjects as a function of the intended speed of movement, by examining the vertical and lateral horizontal components of the ground reaction forces, the frontal plane trajectory of the body center of mass (CM) recorded via motion analysis, and the electromyographic (EMG) recordings of selected lower limb muscles. For the slowest movements, the measured vertical force beneath the flexing and single stance limbs closely matched the vertical force-time history predicted by a quasi-static mechanical model, whereas, the more rapid natural and fast speeds showed progressively larger discrepancies between measured and predicted forces. The initial resultant horizontal force component was exerted in the flexing to stance limb direction but was proportionately greater (41) beneath the flexing versus the stance limb during fast and natural speeds, and became equivalent for slow movements. Speed related EMG differences included an early phasic recruitment of the lateral hip muscle of the flexing limb which always preceded the ground reaction force changes for fast and natural but not slow movements, and a considerably earlier onset of the stance leg knee extensor relative to the flexing limb knee flexor for slow versus fast and natural speeds. Overall, the findings suggested two different speed related strategies for linking the postural and intentional movement components, where the choice of the strategy selected appeared to reflect the mechanical requirements needed to overcome the inertial force of the body mass during transitions from bipedal to single limb stance support.     

Asymmetry of foot position and weight distribution channels the inter-leg coordination dynamics of standing

The study of quiet standing has mainly been conducted in the foot side-by-side position with the assumption that the contribution of the lower limbs is structurally and functionally equivalent. The purpose of this study was to examine how the two mechanical factors of foot position and weight distribution interact to influence postural control and inter-leg coordination dynamics. Participants were required, while standing in either a side-by-side, staggered, or tandem right foot forward position, to intentionally produce three different levels of weight distribution (50/50, 30/70, and 70/30) over the two feet. Our results showed that the interaction effects of the two mechanical constraints were represented in both linear and nonlinear analyses. The center of pressure (COP) mean velocity was predominantly influenced by body weight distribution in the side-by-side stance, whereas foot position was more influential in the tandem stance. The nonlinear analysis showed that the least experienced postural condition (i.e., tandem stance with a 70/30 loading level) had the lowest number and total duration of COP_L–COP_R phase synchronization epochs in the AP direction that were compensated by “stable” coordination dynamics in the ML direction. The findings revealed that the staggered stance represents a “hybrid” blend of the properties of the side-by-side and tandem foot positions. Collectively, foot position and weight distribution interact to determine the stability and flexibility of inter-leg coordination dynamics in postural control.     

Does footedness or hemispheric visual asymmetry influence centre of pressure displacements?

To isolate the footedness contribution from the hemispheric visual asymmetry contribution to the upright postural control, seven right and six left-footed healthy women were asked to balance on each unipodal stance on an unstable platform for each visual hemispaces. We compared lateral deviations of the centre of pressure when balancing on the left leg and on the right leg in three visual conditions: normal and restricted to each hemifields. Whatever the visual conditions, left-footers displaced the centre of pressure towards the outside of the supporting foot, whereas right-footers displaced it towards the right side for the two feet. Postural control appears to be regulated differently between the two groups of footedness. For left-footers it should be more based upon the perception of the centre of body mass and for right-footers upon the asymmetrical utilization of head receptors.     

Do centrally programmed anticipatory postural adjustments in fast stepping affect performance of an associated ”touche” movement?

Ensuring maximum speed in executing a sequence of two voluntary movements requires the second movement to be triggered only after some delay. This is due to the existence of a ”relative refractory period.” If the second movement is initiated during the refractory period, its speed decreases (movement time increases). In the present study we tested the existence of a refractory period during the execution of a sequence of movements involving both the upper and the lower limbs. More precisely, we examined whether the maximal speed of the touche fencing movement is affected by the anticipatory postural adjustments (APA) preceding a voluntary lunge. The touche and the lunge are similar to a pointing task and a stepping forward movement, respectively. touche consists of hitting a target with a foil at maximal velocity. The results show that (a) when the touche was initiated prior to the onset of the APA of the lunge, the maximal foil velocity remains similar to that of an isolated touche, and (b) when the touche is initiated during the development of the APA of the lunge, the maximal foil velocity is lower than in the isolated touche. Furthermore, the maximal foil velocity decreases with the temporal progression of the APA and reaches its minimal value when initiated at the time of voluntary lunge execution (’foot off’). The discussion suggests that the centrally programmed APA that are elicited in the stepping forward movement induces a refractory period which affects performance of the pointing task. Received: 18 January 1999 / Accepted: 22 June 1999