Anticipatory postural adjustments in the shoulder girdle in the reach movement performed in standing by post-stroke subjects

Abstract

After a stroke in middle cerebral artery territory, there is a high probability of dysfunction of the ventromedial pathways, mainly related with postural control mechanisms such as the anticipatory postural adjustments (APAs). According to neuroanatomical knowledge, these pathways have a predominant ipsilesional disposition, which justifies a bilateral postural control dysfunction, often neglected in rehabilitation. In order to assess this bilateral postural control dysfunction, electromyography activity was assessed in eight post-stroke and 10 healthy individuals in the anterior deltoids, the superior and lower trapezius, and the latissimus dorsi as they reached for a bottle with both upper limbs separately at a self-selected velocity and fast velocity while standing associated with trunk kinematics analysis. Through this analysis it was possible to compare the timing of APAs in scapular muscles between sides in post-stroke and with healthy individuals, and to verify if there is a relation between the timing and the displacement of the trunk in the temporal window of the APAs. Indeed, post-stroke individuals show a delayed activation of APAs on scapular girdle muscles on both ipsilesional and contralesional sides, which were not reflected in the trunk displacement.     

Activation timing of soleus and tibialis anterior muscles during sit-to-stand and stand-to-sit in post-stroke vs. healthy subjects

Introduction. Sit-to-stand (SitTS) and stand-to-sit (StandTS) are very important functional tasks that become compromised in stroke patients. As in other voluntary movements, they require an adequate postural control (PC) involving the generation of anticipatory postural adjustments (APAs). In order to give clues for more efficient and directed rehabilitation programs, a deeper knowledge about APAs during challenging and daily life movements is essential.

Purpose. To analyze the activation timing of tibialis anterior (TA) and soleus (SOL) muscles during SitTS and StandTS in healthy subjects and in post-stroke patients.

Methods. Two groups participated in this study: one composed of ten healthy subjects and the other by ten subjects with a history of stroke and increased H-reflex. Electromyographic activity (EMGa) of SOL and TA was analyzed during SitTS and StandTS in the ipsilateral (IPSI) and the contralateral (CONTRA) limb to the side lesion in stroke subjects, and in one limb in healthy subjects. A force plate was used to identify the movement onset.

Results. In both sequences, in the stroke group SOL activation timing occurred prior to movement onset, contrary to the pattern observed in the healthy subjects. Statistically significant differences were found in SOL activation timings between each lower limb of the stroke and healthy groups, but no significant differences were found between the IPSI and the CONTRA limb. The TA activation timing seems to be delayed in the CONTRA limb when compared to the healthy subjects and showed a better organization of TA timing activation in StandTS when compared to SitTS.

Conclusion. Compared to healthy subjects, APAs seem to be altered in both limbs of the post-stroke subjects, with the SOL activation timing being anticipated in both SitTS and StandTS.     

Arm-plane representation of shoulder compensation during pointing movements in patients with stroke

Improvements in functional motor activities are often accompanied by motor compensations to overcome persistent motor impairment in the upper limb. Kinematic analysis is used to objectively quantify movement patterns including common motor compensations such as excessive trunk displacement during reaching. However, a common motor compensation to assist reaching, shoulder abduction, is not adequately characterized by current motion analysis approaches. We apply the arm-plane representation that accounts for the co-variation between movements of the whole arm, and investigate its ability to identify and quantify compensatory arm movements in stroke subjects when making forward arm reaches. This method has not been previously applied to the analysis of motion deficits. Sixteen adults with right post-stroke hemiparesis and eight healthy age-matched controls reached in three target directions (14 trials/target; sampling rate: 100 Hz). Arm-plane movement was validated against endpoint, joint, and trunk kinematics and compared between groups. In stroke subjects, arm-plane measures were correlated with arm impairment (Fugl-Meyer Assessment) and ability (Box and Blocks) scores and were more sensitive than clinical measures to detect mild motor impairment. Arm-plane motion analysis provides new information about motor compensations involving the co-variation of shoulder and elbow movements that may help to understand the underlying motor deficits in patients with stroke.     

Co-activation of upper limb muscles during reaching in post-stroke subjects: An analysis of the contralesional and ipsilesional limbs

The purpose of this study was to analyze the change in antagonist co-activation ratio of upper-limb muscle pairs, during the reaching movement, of both ipsilesional and contralesional limbs of post-stroke subjects. Nine healthy and nine post-stroke subjects were instructed to reach and grasp a target, placed in the sagittal and scapular planes of movement. Surface EMG was recorded from postural control and movement related muscles. Reaching movement was divided in two sub-phases, according to proximal postural control versus movement control demands, during which antagonist co-activation ratios were calculated for the muscle pairs LD/PM, PD/AD, TRIlat/BB and TRIlat/BR. Post-stroke’s ipsilesional limb presented lower co-activation in muscles with an important role in postural control (LD/PM), comparing to the healthy subjects during the first sub-phase, when the movement was performed in the sagittal plane (p < 0.05). Conversely, the post-stroke’s contralesional limb showed in general an increased co-activation ratio in muscles related to movement control, comparing to the healthy subjects. Our findings demonstrate that, in post-stroke subjects, the reaching movement performed with the ipsilesional upper limb seems to show co-activation impairments in muscle pairs associated to postural control, whereas the contralesional upper limb seems to have signs of impairment of muscle pairs related to movement.     

Directional effect on post-stroke motor overflow characteristics

Motor overflow (MO) is an involuntary muscle activation associated with strenuous contralateral movement and may become manifested after stroke. The study was undertaken to investigate physiological correlation underlying atypical directional effect of joint movement on post-stroke MO in the affected upper limb. Thirty patients with unilateral post-stroke hemiparesis and fifteen age-matched healthy controls participated in this study. According to motor function assessed with the Fugl-Meyer arm scale, the patients were categorized into two groups of equal number with better (CVA_G; n = 15) or poorer motor functions (CVA_P; n = 15). Surface electromyography (EMG) was used to record irradiated muscle activation from eight muscles of the affected upper limb when the subjects performed maximal isometric contractions in different directions with the unaffected shoulder, elbow and wrist joints. The results showed that only MO amplitude of the CVA_G and the control groups was more sensitive to variations in direction of joint movement in the unaffected arm than the CVA_P group. The CVA_G group exhibited larger amplitudes of MO than the control analog, whereas this tendency was reversed for the CVA_P group. In terms of EMG polar plots, spatial representations of post-stroke MO were insensitive to direction of contralateral movement. The spatial representations of the CVA_G and CVA_P groups were predominated by potent flexion-abduction synergy, contrary to the typical extension adduction synergy seen in the control analog. In conclusion, post-stroke MO amplitude was subject to contralateral movement direction for healthy controls and stroke patients with better motor recovery. However, alterations in MO spatial pattern due to directional effect were not strictly related to the degree of motor deficits of the stroke victims.     

Effects of stance width on postural movement pattern and anticipatory postural control associated with unilateral arm abduction

We investigated the effects of stance width on postural movement pattern and activation timing of postural muscles during unilateral arm abduction. Thirty-two healthy subjects abducted the right arm at their own timing. Stance width was 0, 9, 18 or 27 cm. Movement angles of leg lateral inclination and trunk lateral flexion to the leg in the frontal plane were analyzed. Based on movement angles at 0 cm width, subjects were classified into three groups: contralateral whole body leaning (CWBLg); ipsilateral trunk flexion (ITFg); and contralateral trunk flexion (CTFg). A high correlation between the movement angles was obtained at 0 cm width (r = 0.82). With increasing stance width, postural movement pattern in the ITFg shifted to patterns characterized by lateral flexion of the trunk toward the side opposite to arm movement, and movement angle of leg-inclination in ITFg and CWBLg decreased. At 0 cm width, left gluteus medius and tensor fascia latae were activated significantly about 40 ms ahead of the right middle deltoid in CWBLg and CTFg, but not in ITFg. However, preceding activation became prominent (about 20 ms) in ITFg for wide stances. Moreover, bilateral activation of the tensor fascia latae was observed in CTFg for all widths.     

Study of the scapular muscle latency and deactivation time in people with and without shoulder impingement

Changes in muscle activities are commonly associated with shoulder impingement and theoretically caused by changes in motor program strategies. The purpose of this study was to assess for differences in latencies and deactivation times of scapular muscles between subjects with and without shoulder impingement. Twenty-five healthy subjects and 24 subjects with impingement symptoms were recruited. Glenohumeral kinematic data and myoelectric activities using surface electrodes from upper trapezius (UT), lower trapezius (LT), serratus anterior (SA) and anterior fibers of deltoid were collected as subjects raised and lowered their arm in response to a visual cue. Data were collected during unloaded, loaded and after repetitive arm raising motion conditions. The variables were analyzed using 2 or 3 way mixed model ANOVAs. Subjects with impingement demonstrated significantly earlier contraction of UT while raising in the unloaded condition and an earlier deactivation of SA across all conditions during lowering of the arm. All subjects exhibited an earlier activation and delayed deactivation of LT and SA in conditions with a weight held in hand. The subjects with impingement showed some significant differences to indicate possible differences in motor control strategies. Rehabilitation measures should consider appropriate training measures to improve movement patterns and muscle control.     

Simulating mechanical consequences of voluntary movement upon whole-body equilibrium: the arm-raising paradigm revisited

Voluntary arm-raising movement performed during the upright human stance position imposes a perturbation to an already unstable bipedal posture characterised by a high body centre of mass (CoM). Inertial forces due to arm acceleration and displacement of the CoM of the arm which alters the CoM position of the whole body represent the two sources of disequilibrium. A current model of postural control explains equilibrium maintenance through the action of anticipatory postural adjustments (APAs) that would offset any destabilising effect of the voluntary movement. The purpose of this paper was to quantify, using computer simulation, the postural perturbation due to arm raising movement. The model incorporated four links, with shoulder, hip, knee and ankle joints constrained by linear viscoelastic elements. The input of the model was a torque applied at the shoulder joint. The simulation described mechanical consequences of the arm-raising movement for different initial conditions. The variables tested were arm inertia, the presence or not of gravity field, the initial standing position and arm movement direction. Simulations showed that the mechanical effect of arm-raising movement was mainly local, that is to say at the level of trunk and lower limbs and produced a slight forward displacement of the CoM (1.5 mm). Backward arm-raising movement had the same effect on the CoM displacement as the forward arm-raising movement. When the mass of the arm was increased, trunk rotation increased producing a CoM displacement in the opposite direction when compared to arm movement performed without load. Postural disturbance was minimised for an initial standing posture with the CoM vertical projection corresponding to the ankle joint axis of rotation. When the model was reduced to two degrees of freedom (ankle and shoulder joints only) the postural perturbation due to arm-raising movement increased compared to the four-joints model. On the basis of these results the classical assumption that APAs stabilise the CoM is challenged.     

Center of Pressure Displacement of Standing Posture during Rapid Movements Is Reorganised Due to Experimental Lower Extremity Muscle Pain

Background

Postural control during rapid movements may be impaired due to musculoskeletal pain. The purpose of this study was to investigate the effect of experimental knee-related muscle pain on the center of pressure (CoP) displacement in a reaction time task condition.

Methods

Nine healthy males performed two reaction time tasks (dominant side shoulder flexion and bilateral heel lift) before, during, and after experimental pain induced in the dominant side vastus medialis or the tibialis anterior muscles by hypertonic saline injections. The CoP displacement was extracted from the ipsilateral and contralateral side by two force plates and the net CoP displacement was calculated.

Results

Compared with non-painful sessions, tibialis anterior muscle pain during the peak and peak-to-peak displacement for the CoP during anticipatory postural adjustments (APAs) of the shoulder task reduced the peak-to-peak displacement of the net CoP in the medial-lateral direction (P<0.05). Tibialis anterior and vastus medialis muscle pain during shoulder flexion task reduced the anterior-posterior peak-to-peak displacement in the ipsilateral side (P<0.05).

Conclusions

The central nervous system in healthy individuals was sufficiently robust in maintaining the APA characteristics during pain, although the displacement of net and ipsilateral CoP in the medial-lateral and anterior-posterior directions during unilateral fast shoulder movement was altered.     

Anticipatory postural adjustments in children with hemiplegia and diplegia

Anticipatory postural adjustments (APAs) play an important role in the performance of many activities requiring the maintenance of standing posture. However, little is known about if and how children with cerebral palsy (CP) generate APAs. Two groups of children with CP (hemiplegia and diplegia) and a group of children with typical motor development performed arm flexion and extension movements while standing on a force platform. Electromyographic activity of six trunk and leg muscles and displacement of center of pressure (COP) were recorded. Children with CP were able to generate anticipatory postural adjustments and produce directionally specific APAs and COP displacements similar to those described in adults and typically developing children. However, children with diplegia were unable to generate APAs of the same magnitude as children with typical development and hemiplegia and had higher baseline muscle activity prior to movement. In children with diplegia, COP was posteriorly displaced and peak acceleration was smaller during bilateral extension compared to children with hemiplegia. The outcomes of the study highlight the role of APAs in the control of posture of children with CP and point out the similarities and differences in anticipatory control in children with diplegia and hemiplegia. These differences may foster ideas for treatment strategies to enhance APAs in children with CP.     

Effects of lateral perturbations and changing stance conditions on anticipatory postural adjustment

The study investigates the role of lateral muscles and changing stance conditions in anticipatory postural adjustments (APAs). Subjects stood laterally to an aluminum pendulum released by an experimenter and were required to stop it with their right or left hand. Stance conditions were manipulated by having the subjects stand in the following positions: on a single limb (SS), with feet together (narrow base of support, NB), and with feet shoulder width apart (regular base of support, RB). Bilateral EMG activity of dorsal, ventral, and lateral trunk and leg muscles and ground reaction forces were recorded and quantified within the time intervals typical of APAs. Anticipatory postural adjustments were seen in all experimental conditions, and their magnitudes depended on the stance and the side of perturbation. Accordingly, APAs in lateral muscles increased on the side of perturbation in SS condition, while simultaneous activation of dorsal muscles occurred on the contralateral side. Smaller APAs were seen in lateral muscles in conditions with a wider base of support (NB, RB) and APAs in dorsal muscles were smaller in NB – in comparison to RB – stance. The results of the present study provide new data on the role of lateral, ventral, and dorsal muscles in anticipatory postural control when dealing with lateral perturbations in conditions of postural instability.     

Electromyography activation of shoulder and trunk muscles is greater during closed chain compared to open chain exercises

BackgroundTo compare the activation of shoulder and trunk muscles between six pairs of closed (CC) and open chain (OC) exercises for the upper extremity, matched for performance characteristics. The secondary aims were to compare shoulder and trunk muscle activation and shoulder activation ratios during each pair of CC and OC exercise.MethodsTwenty-two healthy young adults were recruited. During visit 1, the 5-repetition maximum resistance was established for each CC and OC exercise. During visit 2, electromyography activation from the infraspinatus (INF), deltoid (DEL), serratus anterior (SA), upper, middle and lower trapezius (UT, MT, LT), erector spinae (ES) and external oblique (EO) muscles was collected during 5-repetition max of each exercise. Average activation was calculated during the concentric and eccentric phases of each exercises. Activation ratios (DEL/INF, UT/LT, UT/MT, UT/SA) were also calculated. Linear mixed models compared the activation by muscle collapsed across CC and OC exercises. A paired t-test compared the activation of each muscle and the activation ratios (DEL/INF, UT/LT, UT/MT, UT/SA) between each pair of CC and OC exercises.ResultsThe INF, LT, ES, and EO had greater activation during both concentric (p = 0.03) and eccentric (p < 0.01) phases of CC versus OC exercises. Activation ratios were lower in CC exercises compared to OC exercises (DEL/INF, 3 pairs; UT/LT, 2 pairs; UT/MT, 1 pair; UT/SA, 3 pairs).ConclusionUpper extremity CC exercises generated greater activation of shoulder and trunk muscles compared to OC exercises. Some of the CC exercises produced lower activation ratios compared to OC exercises.     

Cyclic modulation of H-reflex depression in ipsilateral and contralateral soleus muscles during rhythmic arm swing

The objective of the present study was to investigate the effects of rhythmic arm swing on ipsilateral and contralateral soleus motoneuron pool excitability. Ten healthy human subjects participated in this study. Soleus H-reflexes were recorded from the ipsilateral and contralateral soleus muscles while the subject swung the right arm anteroposteriorly as if during gait. The soleus H-reflex was depressed throughout the whole arm swing cycle except in the ipsilateral leg during the onset of the backward arm swing, and in the contralateral leg during the last half of the backward arm swing and the onset of the forward arm swing. The depression was cyclically modulated in accordance with the time course of the arm swing periods, and the pattern of the modulation was reciprocal between the ipsilateral and contralateral legs. This cyclical and reciprocal modulation may be related to the regulation of soleus motoneuron pool excitability during gait.     

Cyclic modulation of H-reflex depression in ipsilateral and contralateral soleus muscles during rhythmic arm swing

The objective of the present study was to investigate the effects of rhythmic arm swing on ipsilateral and contralateral soleus motoneuron pool excitability. Ten healthy human subjects participated in this study. Soleus H-reflexes were recorded from the ipsilateral and contralateral soleus muscles while the subject swung the right arm anteroposteriorly as if during gait. The soleus H-reflex was depressed throughout the whole arm swing cycle except in the ipsilateral leg during the onset of the backward arm swing, and in the contralateral leg during the last half of the backward arm swing and the onset of the forward arm swing. The depression was cyclically modulated in accordance with the time course of the arm swing periods, and the pattern of the modulation was reciprocal between the ipsilateral and contralateral legs. This cyclical and reciprocal modulation may be related to the regulation of soleus motoneuron pool excitability during gait.     

Trunk response to sudden forward perturbations – Effects of preload and sudden load magnitudes,posture and abdominal antagonistic activation

Unexpected loading of the spine is a risk factor for low back pain. The trunk neuromuscular and kinematics responses are likely influenced by the perturbation itself as well as initial trunk conditions. The effect of four parameters (preload, sudden load, initial trunk flexed posture, initial abdominal antagonistic activity) on trunk kinematics and back muscles reflex response were evaluated. Twelve asymptomatic subjects participated in sudden forward perturbation tests under six distinct conditions. Preload did not change the reflexive response of back muscles and the trunk displacement; while peak trunk velocity and acceleration as well as the relative load peak decreased. Sudden load increased reflex response of muscles, trunk kinematics and loading variables. When the trunk was initially flexed, back muscles latency was delayed, trunk velocity and acceleration increased; however, reflex amplitude and relative trunk displacement remained unchanged. Abdominal antagonistic preactivation increased reflexive response of muscles but kinematics variables were not affected. Preload, initial flexed posture and abdominal muscles preactivation increased back muscles preactivity. Both velocity and acceleration peaks of the trunk movement decreased with preload despite greater total load. In contrast, they increased in the initial flexed posture and to some extent when abdominal muscles were preactivated demonstrating the distinct effects of pre-perturbation variables on trunk kinematics and risk of injury.     

An upper extremity kinematic model for evaluation of hemiparetic stroke

Quantification of rehabilitation progress is necessary for accurately assessing clinical treatments. A three-dimension (3D) upper extremity (UE) kinematic model was developed to obtain joint angles of the trunk, shoulder and elbow using a Vicon motion analysis system. Strict evaluation confirmed the system's accuracy and precision. As an example of application, the model was used to evaluate the upper extremity movement of eight hemiparetic stroke patients with spasticity, while completing a set of reaching tasks. Main outcome measures include kinematic variables of movement time, range of motion, peak angular velocity, and percentage of reach where peak velocity occurs. The model computed motion patterns in the affected and unaffected arms. The unaffected arm showed a larger range of motion and higher angular velocity than the affected arm. Frequency analysis (power spectrum) demonstrated lower frequency content for elbow angle and angular velocity in the affected limb when compared to the unaffected limb. The model can accurately quantify UE arm motion, which may aid in the assessment and planning of stroke rehabilitation, and help to shorten recovery time.     

The recruitment order of scapular muscles depends on the characteristics of the postural task

Previous studies show that the scapular muscle recruitment order could possibly change according to the characteristics of the postural task. We aimed to compare the activation latencies of serratus anterior (SA), upper, middle, and lower trapezius (UT, MT and LT, respectively) between an unpredictable perturbation (sudden arm destabilization) and a predictable task (voluntary arm raise) and, to determine the differences in the muscle recruitment order in each task. The electromyographic signals of 23 participants were recorded while the tasks were performed. All scapular muscles showed earlier onset latency in the voluntary arm raise than in the sudden arm destabilization. No significant differences were observed in the muscle recruitment order for the sudden arm destabilization (p > 0.05). Conversely, for voluntary arm raise the MT, LT SA and anterior deltoid (AD) were activated significantly earlier than the UT (p < 0.001). Scapular muscles present a specific recruitment order during a predictable task: SA was activated prior to the AD and the UT after the AD, in a recruitment order of SA, AD, UT, MT, and LT. While in an unpredictable motor task, all muscles were activated after the destabilization without a specific recruitment order, but rather a simultaneous activation.     

The effect of short-term changes in body mass distribution on feed-forward postural control

It was recently shown that short-term changes in the whole body mass and associated changes in the vertical position of the center of mass (COM) modify anticipatory postural adjustments (APAs) [Li X, Aruin AS. The effect of short-term changes in the body mass on anticipatory postural adjustments. Exp Brain Res 2007;181:333–46]. In this study, we investigated whether changes in the body mass distribution and related changes in the anterior–posterior COM position affect APA generation. Fourteen subjects were instructed to catch a 2.2 kg load with their arms extended while standing with no additional weight or while carrying a 9.08 kg weight. Adding weight to a backpack, front pack or belly pocket was associated with an increase of the whole body mass, but it also involved changes in the anterior–posterior (A/P) and vertical positions of the COM. Electromyographic activity of leg and trunk muscles, body kinematics, and ground reaction forces were recorded and quantified within the typical time intervals of APAs. APAs were modified in conditions with changed body mass distribution: increased magnitude of anticipatory EMG activity in leg and trunk muscles, as well as co-activation of leg muscles and decreased anticipatory displacement of the COM in the vertical direction, were seen in conditions with increased body mass. Changes in the COM position induced in both A/P and vertical directions were associated with increased anticipatory EMG activity. In addition, they were linked to a co-activation of muscles at the ankle joints and significant changes in the center of pressure (COP) position. Modifications of the COM position induced in the A/P direction were related to increased anticipatory EMG activity in the leg and trunk muscles. At the same time, no significant differences in anticipatory EMG activity or displacement of COP were observed when changes of COM position were induced in the vertical direction. The study outcome suggests that the CNS uses different strategies while generating APAs in conditions with changes in the COM position induced in the anterior–posterior and vertical directions.     

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.     

Electromyography study of six parts of the latissimus dorsi during reaching tasks while seated: A comparison between healthy subjects and stroke patients

PurposeTo compare the excitation of the six different segments of the latissimus dorsi (LD) while reaching different distances and in different directions in stroke patients and healthy controls.MethodSurface electromyography was used to measure the excitation of the LD segments (LD1-LD6) in 12 chronic stroke patients and 11 healthy controls during reaching tasks. A target was placed in the sagittal and scapular planes at arm’s length, 125% of arm's length, and maximum reaching distance. The clinical trial registration number is NCT04181151 (date of registration November 25, 2019).ResultsThe excitation of the LD segments during the arm’s length reaching task was similar between the groups (p greater than 0.05). The excitation of LD1, LD2, and LD5 in the sagittal plane and of LD1, LD2, LD3, and LD5 in the scapular plane was higher during the reaching 125% of arm’s length task compared to the controls (p < 0.05). During the maximum reaching task, the excitation of LD1 was higher in the stroke patients in both the sagittal and scapular planes (p < 0.05).ConclusionThe excitation of the LD segments was influenced by the direction and distance of the reaching in the stroke patients. The results of this study may help us to better understand how the LD behaves after stroke and to design rehabilitation approaches with a greater focus on the LD.