Qualitative discrepancies between trunk muscle activity and dynamic postural requirements at the initiation of reaching movements performed while sitting

Postural control during turn on the light task assisted by functional electrical stimulation in post stroke subjects

Postural control mechanisms have a determinant role in reaching tasks and are typically impaired in post-stroke patients. Functional electrical stimulation (FES) has been demonstrated to be a promising therapy for improving upper limb (UL) function. However, according to our knowledge, no study has evaluated FES influence on postural control. This study aims to evaluate the influence of FES UL assistance, during turning on the light task, in the related postural control mechanisms. An observational study involving ten post-stroke subjects with UL dysfunction was performed. Early and anticipatory postural adjustments (EPAs and APAs, respectively), the weight shift, the center of pressure and the center of mass (CoM) displacement were analyzed during the turning on the light task with and without the FES assistance. FES parameters were adjusted to improve UL function according to a consensus between physiotherapists' and patients' perspectives. The ANOVA repeated measures, Paired sample t and McNemar tests were used to compare postural control between the assisted and non-assisted conditions. When the task was assisted by FES, the number of participants that presented APAs increased (p = 0.031). UL FES assistance during turning on the light task can improve postural control in neurological patients with UL impairments.

Improving Upper Extremity Strength, Function, and Trunk Stability Using Wide-Pulse Functional Electrical Stimulation in Combination With Functional Task-Specific Practice

Objectives

To evaluate upper extremity (UE) function, strength, and dynamic sitting balance in individuals with spinal cord injury (SCI) who received an intensive outpatient therapy program focused on UE training augmented with wide pulse/high frequency functional electrical stimulation (WPHF-FES).

Methods

This prospective case series was conducted in an outpatient (OP) clinic in an SCI-specific rehabilitation hospital. Participants were a convenience sample (N = 50) of individuals with tetraplegia receiving OP therapy focused on UE recovery. Individuals participated in 60 minutes of UE functional task-specific practice (FTP) in combination with WPHF-FES 5 times/week for an average of 72 sessions. The primary outcome for this analysis was the Capabilities of Upper Extremity Test (CUE-T). Secondary outcomes include UE motor score (UEMS) and the modified functional reach (MFR).

Results

Fifty individuals (13 motor complete; 37 motor incomplete SCI) completed an OP UE training program incorporating WPHF-FES and were included in this analysis. On average, participants demonstrated significant improvements in the total CUE-T score of 14.1 (SD = 10.0, p < .0001) points; significant changes were also noted in UEMS and MFR, improving an average of 4.6 (SD = 5.2, p < .0001) points and 13.6 (SD = 15.8, p < .0001) cm, respectively.

Conclusion

Individuals with tetraplegia demonstrated significant improvements in UE strength, function, and dynamic sitting trunk balance after receiving UE training augmented with WPHF-FES. Future comparative effectiveness studies need to be completed to guide efficacious treatment interventions in OP therapy.

Constancy of Preparatory Postural Adjustments for Reaching to Virtual Targets across Different Postural Configurations

Postural and movement components must be coordinated without significant disturbance to balance when reaching from a standing position. Traditional theories propose that muscle activity prior to movement onset create the mechanics to counteract the internal torques generated by the future limb movement, reducing possible instability via centre of mass (CoM) displacement. However, during goal-directed reach movements executed on a fixed base of support (BoS), preparatory postural adjustments (or pPAs) promote movement of the CoM within the BoS. Considering this dichotomy, the current study investigated if pPAs constitute part of a whole-body strategy that is tied to the efficient execution of movement, rather than the constraints of balance. We reasoned that if pPAs were tied primarily to balance control, they would modulate as a function of perceived instability. Alternatively, if tied to dynamics necessary for movement initiation, they would remain unchanged, with feedback-based changes being sufficient to retain balance following volitional arm movement. Participants executed beyond-arm reaching movements in four different postural configurations that altered the quality of the BoS. Quantification of these changes to stability did not drastically alter the tuning or timing of preparatory muscle activity despite modifications to arm and CoM trajectories necessary to complete the reaching movement. In contrast to traditional views, preparatory postural muscle activity is not always tuned for balance maintenance or even as a calculation of upcoming instability but may reflect a requirement of voluntary movement towards a pre-defined location.

A comparison of the relationship between manual dexterity and postural control in young and older individuals with Parkinson's disease

The motor symptoms of Parkinson's disease (PD) cause deterioration in manual dexterity. This deterioration affects independence in activities of daily living negatively. The loss of postural control, which occurs more frequently with disease progression, restricts physical functions and reduces mobility in patients with PD. Impaired postural control may affect distal mobility of an individual. The aim of this study was to investigate postural control and manual dexterity in individuals ≤ 65 and >65 years with PD and analyze the relationship between these variables according to age. Sixty-six individuals with PD participated in the study. The participants were categorized according to age (n = 29 for 65 years of age or younger and n = 37 for older). Manual dexterity (Dominant and Non-dominant hand) was assessed by the Nine Hole Peg Test (NHPT). Postural control was evaluated by the Limit of Stability Test (LoS) using a computerized balance measuring instrument. There was no statistically significant difference between the age groups on the combined dependent variables after controlling for disability, gender, weight, and height; F(7, 54) = 0.804, p = 0.587. Only LoS-Maximum Excursion was higher in the individuals ≤ 65 years (p = 0.035). Significant correlations were found between NHPT-Dominant and LoS-Reaction Time, LoS-Maximum Excursion; NHPT-Non-dominant and LoS-Reaction Time, LoS-Endpoint Excursion, LoS-Maximum Excursion in the older group (p < 0.05). There was no difference manual dexterity and postural control according to age except for LoS-Maximum Excursion. LoS-Maximum Excursion was higher in the young group. The manual dexterity was associated with postural control in individuals over 65 years of age with PD; however, not associated in younger individuals.

POSTURAL CONTROL ASSESSMENT IN PHYSICALLY ACTIVE AND SEDENTARY INDIVIDUALS WITH PARAPLEGIA

Objective:

The aim of this study was to evaluate functional independence and trunk control during maximum-range tasks in individuals with spinal cord injuries, who were divided into sedentary (SSI, n=10) and physically active (PASI, n=10) groups .

Methods:

Anamnesis was conducted and level and type of injury were identified (according to the American Spinal Injury Association protocol, ASIA) and the Functional Independence Measure (FIM) questionnaire was applied. For the forward and lateral reach task, the subjects were instructed to reach as far as possible. Mean data were compared using the unpaired t test and Mann-Whitney test and differences were considered significant when p<0.05 .

Results:

The PASI group performed better in self-care activities (PASI: 40.8±0.42 points, SSI: 38.0±3.58 points, p=0.01), sphincter control (PASI: 10.5±1.84 points, SSI: 8.2±3.04 points, p=0.02), transfers (PASI: 20.7±0.48 points, SSI: 16.9±4.27 points, p=0.04), and total FIM score (PASI: 104.0±2.30 points, SSI 105.1±8.56 points, p=0.01). On the maximum reach task, the PASI group had a greater average range in all directions evaluated (p<0.05) .

Conclusion:

The continuous practice of exercise increased motor function independence and trunk control in individuals with complete spinal cord injury. Level of Evidence II, Prospective Comparative Study.

Trunk muscles contribute as functional groups to directionality of reaching during stance

Muscle activity preceding the onset of voluntary movement has been shown to reduce centre of mass (CoM) displacement and stabilise the body during self-induced 'perturbations'. However, based on recent findings in the lower limb, where preparatory muscle activity creates the dynamics necessary for the initiation of movement, this study sought to investigate whether trunk musculature acted consistently to minimise the displacement of the CoM, or in contrast, contribute to the movement. While standing, nine healthy participants made single-step (point-to-point) reaching movements to 13 visual targets throughout a 180° range (target interval = 15°). Full-body kinematics and electromyographic activity from 'focal' arm and 'postural' trunk muscles were analysed for a preparatory phase of 250-ms preceding movement onset (termed pPA). Akin to lower limb findings, direction-specific patterns of anticipatory trunk muscle activity accompanied the onset of rotational kinematics and CoM acceleration in the direction of the desired target. When arranged in terms of peak activation, we found functionally relevant groupings aligned to either ipsi-, central or contra-lateral reaching directions. Contrary to traditional approaches, which focus on CoM stabilisation, this spatial recruitment was in favour of assisting initiation of movement. Such activity suggests that the central nervous system may rely on synergic patterns of muscle activation within an undistinguishable and shared focal/postural motor command for functional voluntary movements.

Trunk strength and function using the multidirectional reach distance in individuals with non-traumatic spinal cord injury

CONTEXT

Trunk control is essential to engage in activities of daily living. Measuring trunk strength and function in persons with spinal cord injury (SCI) is difficult. Trunk function has not been studied in non-traumatic SCI (NTSCI).

OBJECTIVES

To characterize changes in trunk strength and seated functional reach in individuals with NTSCI during inpatient rehabilitation. To determine if trunk strength and seated reach differ between walkers and wheelchair users. To explore relationships between trunk and hip strength and seated functional reach.

DESIGN

Observational study.

SETTING

Two SCI rehabilitation facilities.

PARTICIPANTS

32 subacute inpatients (mean age 48.0 ± 15.4 years).

OUTCOME MEASURES

Isometric strength of trunk and hip and function (Multidirectional Reach Test: MDRT) were assessed at admission and within 2 weeks of discharge. Analysis of variance was conducted for admission measures (MDRT, hip and trunk strength) between walkers and wheelchair users. Changes in MDRT, hip and trunk strength were evaluated using parametric and non-parametric statistics. The level of association between changes in values of MRDT and strength was also examined.

RESULTS

Significant differences between walkers and wheelchair users were found for strength measures (P < 0.05) but not for MDRT. Left- and right-sided reaches increased in wheelchair users only (P < 0.05). Associations between changes in hip strength, trunk strength, and reach distance were found (R = 0.67-0.73).

CONCLUSION

In clinical settings, it is feasible and relevant to assess trunk, hip strength, and MRDT. Future studies require strategies to increase the number of participants assessed, in order to inform clinicians about relevant rehabilitation interventions.

Incomplete Posture Adjustment during Rapid Arm Movement

It is not well understood how posture (nonfocal joints) is stabilized during rapid joint movements. Interaction torque arising at the joints due to the movement of the adjacent joints will disturb the nonfocal joint unless it is compensated by muscle torque. The aim of this study was to clarify the mechanism underlying the incomplete stabilization of nonfocal posture during two types of fast single-joint flexion tasks, i.e., elbow flexion and shoulder flexion, with and without a hand-held weight. Participants were 5 men and 4 women ( M age = 22.2 yr., SD = 4.8). The relationship between interaction torque and muscle torque and between angular displacement and torque components of the nonfocal joints were examined. The anticipatory muscle activity at the nonfocal joint produced compensatory muscle torque during the early phase of the rapid movement. However, nonfocal joints displayed a consistent displacement pattern, i.e., an initial extension followed by a flexion during the movement. The initial extension was in the direction of the interaction torque and its magnitude was related to the onset delay of the muscle torque against the interaction torque. The flexion movement of the nonfocal joints during the task was in the direction of the overcompensating muscle torque against interaction torque. This mechanism may have certain implications for anticipatory postural adjustment problems.

Trunk posture affects upper extremity function of adults

This study examined the effects of various seated trunk postures on upper extremity function. 59 adults were tested using the Jebsen Taylor Hand Function Test while in three different trunk postures. Significant mean differences between the neutral versus the flexed and laterally flexed trunk postures were noted during selected tasks. Specifically, dominant hand performance during the tasks of feeding and lifting heavy cans was significantly slower while the trunk was flexed and laterally flexed than when performed in the neutral trunk position. Performance of the nondomi nant hand during the tasks of picking up small objects, page turning, as well as the total score was slower while the trunk was flexed compared to performance in the neutral trunk position. These findings support the assumption that neutral trunk posture improves upper extremity performance during daily activities although the effect is not consistent across tasks. Findings are discussed along with limitations and recommendations for research.

Human whole-body reaching in normal gravity and microgravity reveals a strong temporal coordination between postural and focal task components

Previous experiments by our group in normal gravity (1 G) have revealed spatial relationships between postural and focal components of whole-body reaching and pointing movements. We suggested that these relationships could be explained partly through the use of gravity to displace the CoM and attain the object or target position. In this study we compared human whole-body reaching in 1 G and microgravity (0 G) in order to more fully investigate how gravity contributes to strategies adopted for task execution and to determine possible invariant temporal relationships between multiple segments. Whole-body reaching movements made from the standing position in two experimental conditions of execution speed (naturally paced and as fast as possible) were recorded during periods of 1 G and 0 G in parabolic flight. Overall, at each speed of reaching, movement times were significantly slower when performed in 0 G than in 1 G for two of the three subjects, but all subjects were able to produce significantly faster movements in 0 G than in 1 G. Despite similar general trends across subjects observed in 1 G, angular displacements of reaching movements performed in 0 G differed greatly between subjects. There were changes at all joints, but above all at the shoulder and the ankle. However, despite a high intersubject and intratrial variability in 0 G, in both gravity conditions all subjects demonstrated times to peak curvilinear velocity for the finger (end effector) and the whole-body centre of mass (CoM) that coincided, regardless of the speed of execution. Moreover, cross-correlations between multiple segment curvilinear velocities and those of the CoM revealed tight, highly correlated temporal relationships between segments proximal to the CoM (which was expected). However, for more distal segments, the correlations were weaker, and the movements lagged behind movements of the CoM. The major and most interesting finding of this study was that although the finger was the most distal within the segment chain, with respect to the CoM, it was highly correlated with the CoM (0.99--0.98, all conditions) and with no time lag. Despite the large intersubject and inter-environmental variability recorded in this study, temporal relationships between postural task components (CoM displacements) and those of the focal movement (end-effector trajectory) were consistently conserved.

Timing of muscle activity during reaching while standing: systematic changes with target distance

We examined the effects of changing target distance from within arm's length (AL) to beyond arm's length on the onsets of electromyographic (EMG) activity of non-focal muscles for a reaching task performed while standing. Two questions were addressed. First, do changes in target distance result in consistent changes in the onsets of non-focal anticipatory muscle activity of the trunk and legs in healthy subjects? Second, do changes in onsets of all non-focal muscles vary in a similar fashion in response to varying target distance? Thirteen young, healthy adults performed rapid, bilateral reaching movements to targets placed at shoulder height at four distances while electromyographic activity was recorded from muscles of the arm, trunk and legs. Ground reaction forces and arm kinematics were also recorded. The onsets of most non-focal muscles occurred prior to the onset of arm movement, and occurred progressively earlier as target distance was increased. An exception to this trend was the onset of the erector spinae muscle, which occurred progressively later as target distance was increased. These data support the notion that reaches to targets beyond arm's length involve anticipatory non-focal muscle activity that acts to transport the arm to the target rather than simply to resist the perturbation caused by the arm movement. The consistent patterns of anticipatory muscle activity observed in healthy subjects provide a template against which to compare activity patterns of non-focal muscles for individuals with potential deficits in the control of standing balance.

Does postural chain mobility influence muscular control in sitting ramp pushes?

This study was conducted under the hypothesis that voluntary movement involves a perturbation of body balance and that a counter-perturbation has to be developed to limit the perturbation effects, which is a condition necessary to perform the movement efficiently. The stabilising action is produced in body segments that constitute the "postural" chain, and the voluntary movement by the segments said to constitute the "focal" chain. In order to deepen the understanding of how the postural chain contributes to the motor act, isometric transient efforts were considered. Seven adults in a sitting posture were instructed to exert bilateral horizontal pushes on a dynamometric bar, as rapidly as possible, up to their maximal force (Fx). Two sitting conditions were considered: full ischio-femoral contact (100 BP) and one-third ischio-femoral contact (30 BP), the latter being known to yield greater pelvis and spine mobility, that is greater postural mobility. Each session consisted of ten maximal pushes for each sitting condition. In order to explore the influence of postural mobility on muscular control and push force, surface EMGs of 14 postural and focal muscles were recorded. In addition, reaction forces (Rx) and displacement (Xp) of the centre of pressure (along the anteroposterior axis) were measured, as well as iliac crest acceleration (xh and zh, along the anteroposterior and vertical axes, respectively). The results showed that push force varied abruptly during the task ramp effort. When the ischio-femoral contact was limited, push force was enhanced, as well as the rate of push force rise (Fx/Deltat, Deltat being the force rise duration), suggesting a greater perturbation to balance. Also, there were significant increases in the Rx reaction forces, indicating body segment acceleration: "dynamic" phenomena occurred in the articulated body chain in response to increases in Fx. In addition, even though muscular contraction was isometric, postural EMGs, as well as focal EMGs, were phasic, a feature which characterises transient force exertion. The Rx reaction forces were associated with backward displacement of the centre of pressure, Xp. The centre of pressure displacement was interpreted as a backward pelvis rotation, an interpretation which was confirmed by backward and upward iliac crest accelerations. When ischio-femoral contact was reduced, the backward pelvis rotation was significantly increased, resulting from an increased pelvis and spine mobility. Distinct focal and postural EMG sequences were found to be associated with the effort. Two different sets of muscles were observed when considering recruitment order, the focal and the postural muscles. The ankle muscles were activated before the pelvis, the back and the scapular girdle, with the upper limb muscles activated only after the onset of the primum movens of push action (serratus anterior): the activation process followed a distal to proximal progression order. Moreover, the postural EMG sequence was anticipatory, that is there were anticipatory postural adjustments (APAs). Modifying the ischio-femoral contact did not induce a change in either the postural muscle set or in the recruitment order. There were significant increases in the level of activation (integrated EMG) of the postural muscles when ischio-femoral contact was reduced. They did not result from an increase in EMG duration but only from a modulation of EMG amplitude, suggesting that postural control for different ischio-femoral contacts involves adapting the motor program according to the postural requirements, rather than changing the postural strategy. Moreover, as APA amplitude was increased when ischio-femoral contact was reduced, it could be assumed that the postural chain is programmed in relation to postural chain mobility. In addition, the increase in postural EMGs was interpreted as an increased counter-perturbation opposed to an increased push force. It is concluded that greater mobility of the postural chain favours a greater dynamic counter-perturbat chain favours a greater dynamic counter-perturbation, which, in turn, allows the development of a greater push force; the ability to develop such a counter-perturbation (termed PKC: posturo-kinetic capacity) is enhanced when postural chain mobility is greater. Postural chain mobility appears to be a task parameter, and postural control appears to involve adapting the motor program according to the postural requirements, rather than changing the postural strategy.

Trunk control in unstable sitting posture during functional activities in healthy subjects and patients with multiple sclerosis

OBJECTIVE

To examine trunk stability in unstable sitting posture in 2 different functional activities.

DESIGN

A randomized crossover design.

SETTING

Rehabilitation center in Italy.

PARTICIPANTS

Ten healthy subjects and 10 patients with multiple sclerosis.

INTERVENTIONS

Subjects were seated on an unstable support surface. A task in which the subjects had to keep their trunk as stable as possible was compared with tasks in which they had to track an object with the head or grasp an object.Main outcome measures Angular displacement and mean absolute angular velocity in the anteroposterior and mediolateral planes of the support surface.

RESULTS

Angular displacement showed differences between patients and healthy subjects both in the sagittal plane (P<.0001) and frontal plane (P<.002). Velocity of angular displacement differentiated between the groups in both planes (P<.0001). Differences between velocity of angular displacement in different tasks were also detected (P<.0001). Correlation coefficients between sitting balance scores and laboratory measures were low and not statistically significant. In the healthy subjects, instability in the frontal plane correlated positively with the subjects' weight and height.

CONCLUSIONS

Both patients and healthy subjects had more difficulty with frontal plane stability than with sagittal plane stability. Angular velocity for a given task showed the greatest difference between the groups and between postural challenge tasks within a group. Patients were more unstable than healthy subjects during head movements in the frontal plane; conversely, arm movements produced larger angular displacement, especially in the sagittal plane.

Trajectories of target reaching arm movements in individuals with spinal cord injury: effect of external trunk support

DESIGN

Deficits in trunk control due to spinal cord injury (SCI) lead to slower target-reaching movements of the hand. We investigated whether the movement path is also affected, and whether providing external support for the trunk can abolish the kinematic differences.

OBJECTIVE

To compare movement trajectories between individuals with SCI and neurologically normal individuals, with and without external trunk support.

SETTING

Neural Control/Biomechanics Laboratory, University of Illinois, Chicago, USA.

METHODS

Five subjects with levels of injury between C7 and T4 were tested 3-8 years post-injury, and compared with five control subjects. Two targets were employed. Trajectories were recorded by a motion-capture system using infrared emitting markers. Peak speed and path curvature were calculated for the fingertip and for the acromion.

RESULTS

Compared with control subjects, the subjects with SCI exhibited lower peak speed of the fingertip but not of the acromion, and less straight paths for both. When the trunk was supported externally, the difference in fingertip speed persisted. The support abolished the difference in path curvature for the fingertip but accentuated that for the acromion.

CONCLUSION

The slower hand movements of individuals with SCI are not simply time-scaled versions of those of normal subjects, and the provision of trunk support does not erase the kinematic differences between the reaching movements of the two groups.

A sequence of postural muscle excitations precedes and accompanies isometric ramp efforts performed while sitting in human subjects

The purpose of this study was to explore how the muscles which control postural body segments are activated during bilateral isometric ramp pushes exerted with the upper limbs by seated subjects. The paradigm under study presents the advantage that the subject is in a quasi-static posture, and since upper limbs are stretched out, the dynamic phenomena, which might occur, can only originate from the rest of the body, which means from the postural chain. A dynamometer was used to measure the horizontal force, Fx, exerted on the bar, and a custom-designed force-plate was used to measure global reaction forces (Rx) and displacement of the centre of pressure (Xp) along the antero-posterior axis. Electromyograms (EMGs) were picked up by bipolar surface electrodes from 14 muscles crossing the lower limb, pelvis, trunk and upper limb joints. It was shown that transient push efforts require monotonous EMG increase in postural as well as in focal muscles. The EMG sequence starts with the postural muscles and ends with the focal ones. The postural EMG sequence is anticipatory. It is concluded that the EMG sequence is programmed according to the task parameters, and that its role is to counteract in advance the perturbing effect of the effort, in order to allow the effort to be performed efficiently. It is suggested that excitation between the postural muscles is distributed according to their biomechanical role in relation to the supports.

Three dimensional preparatory trunk motion precedes asymmetrical upper limb movement

Three-dimensional trunk motion, trunk muscle electromyography and intra-abdominal pressure were evaluated to investigate the preparatory control of the trunk associated with voluntary unilateral upper limb movement. The directions of angular motion produced by moments reactive to limb movement in each direction were predicted using a three-dimensional model of the body. Preparatory motion of the trunk occurred in three dimensions in the directions opposite to the reactive moments. Electromyographic recordings from the superficial trunk muscles were consistent with preparatory trunk motion. However, activation of transversus abdominis was inconsistent with control of direction-specific moments acting on the trunk. The results provide evidence that anticipatory postural adjustments result in movements and not simple rigidification of the trunk.