Postural Strategies Research Articles

Postural Stability in Single-Leg Quiet Stance in Highly Trained Athletes: Sex and Sport Differences.

This study aimed to determine if there is a difference in postural stability in highly trained adolescents and young adult athletes regarding sex and sport. The participants were young athletes (n = 464) from seven different sports. We considered the center of pressure (CoP) velocity (total, anterior–posterior (AP) and medial–lateral (ML)), CoP amplitude (AP and ML), and CoP frequency (AP and ML), as assessed by single-leg quiet stance test. Significant interactions were found between sex and sport for all CoP variables (p < 0.02). Additionally, a significant main effect of sport was also found in all CoP variables (p = 0.01). Regarding sex, significant effects were found for all CoP amplitude variables (p = 0.01), as well as for CoP velocity variables, except for CoP ML (p = 0.06). Moreover, there was no sex effect for CoP frequency AP (p = 0.18). The results of the current study confirm the claim that the criteria for optimal postural strategies for elite athletes likely depend on a given sport.

Balance on different unstable supports: a complementary approach based on linear and non-linear analyses.

Maintenance of postural control is a complex task that requires the integration of different sensory-motor processes. To improve postural control, balance training is often implemented using unstable surfaces. Little is known, however, about how different surfaces compare in terms of postural control strategy. Non-linear dynamical system analysis, like recurrent quantification analysis (RQA) applied to the center of pressure (CoP) trajectory, represents a useful tool in this respect. The aim of this study is to investigate the effects of different unstable supports on the CoP trajectory through a complementary approach based on linear and non-linear analyses. Seventeen healthy adults performed barefoot single-leg balance trials on a force plate and on three different balance training devices (soft disc, foam pad, and pillow). Sets of parameters were extracted from the CoP trajectories using classical stabilometric analysis (sway path, mean velocity, root mean square) and RQA (percent recurrence and determinism, maximum line length, entropy). Both classical and RQA analyses highlighted significant differences between stable (force plate) and unstable conditions (p < 0.001). Conversely, only classical stabilometric parameters showed significant differences among the considered balance training devices, indicating that the different characteristics of the devices do not influence the dynamic/temporal structure of the CoP trajectory. Analysis of the center of pressure trajectory during single-leg standing on three different balance training devices and on a rigid surface using both linear and non-linear techniques.

Effects of unilateral and bilateral lower extremity fatiguing exercises on postural control during quiet stance and self-initiated perturbation.

Postural control can be more difficult during muscle fatigue. Anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs) are the two main postural strategies controlled by the central nervous system. Unchanged or early anticipatory onset together with altered activation magnitude during the APAs phase is observed in the trunk and thigh muscles following unilateral and bilateral fatiguing exercises. Thus far, no studies have compared the effect of such exercises on APAs and CPAs. This study compared the effects of these exercises performed at the same relative workload on center of pressure (COP)-based postural stability measures during quiet stance and electromyography (EMG)-based APAs and CPAs during self-initiated perturbation. Fifteen young male subjects completed the two separated fatiguing sessions; 50% of maximal voluntary contraction force obtained from the unilateral (dominant) and bilateral legs with five sets of 20 times lower limb exercise was respectively applied as unilateral and bilateral fatiguing protocols. Spatio-temporal COP parameters (sway velocity, total displacement, and envelope area) were used to evaluate postural stability, and spectral analysis was performed to estimate the distributions in COP power spectrum. EMG activities of transversus abdominis/internal oblique (TrA/IO) and lumbar multifidus (LMF) were recorded and analyzed during the APAs and CPAs phases. Increased sway velocity and total displacements occurred following both unilateral and bilateral fatiguing exercises; however, the envelope area was not affected. Further, early anticipatory onset of TrA/IO was found after bilateral than after unilateral fatiguing exercise. Co-activation index of the TrA/IO-LMF muscle pair during the CPAs phase increased following both fatiguing sessions. The results partly confirmed previously reported fatigue effects induced by unilateral and bilateral exercises on postural stability. It was observed that APAs onsets were altered differently following a unilateral or bilateral fatiguing exercise, whereas the alterations of CPAs were independent of fatigue conditions. Repetitive unilateral or bilateral fatiguing exercises in patients or athletes may differently alter the anticipatory component of postural control.

An adaptive force and posture control strategy for automated wiring terminal assembly

ABSTRACT Mainstream industrial practice of assembling different flexible wires into the connector is manual due to different specifications of terminals and flexible wire assembly requirements. Therefore, the efficiency of the production and the quality of the assembly rely heavily on the knowledge and experiences of human workers. To reduce the labor cost and possible errors, this paper presents an adaptive force and posture control strategy for automated wiring terminal assembly (WTA). The contact force states during the search phase and insertion phase are first analyzed and then modeled. With the force analysis, fuzzy-PID controllers are applied for translational and angular adjustment during the assembly process. To validate the control strategy proposed, a prototype system is set up by integrating a force/torque (F/T) sensor and cameras on an industrial robot. And two kinds of industrial wires with four types of different wire terminals are tested with comparative studies. The results have shown that the proposed control strategy is able to conduct automatic insertion with different flexible wires successfully with reliable force feedback.

Walking on Mild Slopes and Altering Arm Swing Each Induce Specific Strategies in Healthy Young Adults.

Slopes are present in everyday environments and require specific postural strategies for successful navigation; different arm strategies may be used to manage external perturbations while walking. It has yet to be determined what impact arm swing has on postural strategies and gait stability during sloped walking. We investigated the potentially interacting effects of surface slope and arm motion on gait stability and postural strategies in healthy young adults. We tested 15 healthy adults, using the CAREN-Extended system to simulate a rolling-hills environment which imparted both incline (uphill) and decline (downhill) slopes (± 3°). This protocol was completed under three imposed arm swing conditions: held, normal, active. Spatiotemporal gait parameters, mediolateral margin of stability, and postural kinematics in anteroposterior (AP), mediolateral (ML), and vertical (VT) directions were assessed. Main effects of conditions and interactions were evaluated by 2-way repeated measures analysis of variance. Our results showed no interactions between arm swing and slope; however, we found main effects of arm swing and main effects of slope. As expected, uphill and downhill sections of the rolling-hills yielded opposite stepping and postural strategies compared to level walking, and active and held arm swings led to opposite postural strategies compared to normal arm swing. Arm swing effects were consistent across slope conditions. Walking with arms held decreased gait speed, indicating a level of caution, but maintained stability comparable to that of walking with normal arm swing. Active arm swing increased both step width variability and ML-MoS during downhill sections. Alternately, ML-MoS was larger with increased step width and double support time during uphill sections compared to level, which demonstrates that distinct base of support strategies are used to manage arm swing compared to slope. The variability of the rolling-hills also required proactive base of support changes despite the mild slopes to maintain balance.

Postural Control Differences between Patients with Posterior Tibial Tendon Dysfunction and Healthy People during Gait.

Background: Patients with posterior tibial tendon dysfunction (PTTD) may exhibit postural instability during walking likely due to a loss of medial longitudinal arch, abnormal foot alignment, and pain. While many studies have investigated gait alterations in PTTD, there is no understanding of dynamic postural control mechanisms in this population during gait, which will help guide rehabilitation and gait training programs for patients with PTTD. The purpose of the study was to assess dynamic postural control mechanisms in patients with stage II PTTD as compared to age and gender matched healthy controls. Methods: Eleven patients with stage II PTTD (4 males and 7 females; age 59 ± 1 years; height 1.66 ± 0.12 m; mass 84.2 ± 16.0 kg) and ten gender and age matched controls were recruited in this study. Participants were asked to walk along a 10 m walkway. Ten Vicon cameras and four AMTI force platforms were used to collect kinematic and center of pressure (COP) data while participants performed gait. To test differences between PTTD vs. control groups, independent t-tests (set at α < 0.05) were performed. Results: Patients with PTTD had significantly higher double stance ratio (+23%) and anterior-posterior (AP) time to contact (TTC) percentage (+16%) as compared to healthy control. However, PTTD had lower AP COP excursion (−19%), AP COP velocity (−30%), and medial-lateral (ML) COP velocity (−40%) as compared to healthy controls. Mean ML COP trace values for PTTD were significantly decreased (−23%) as compared to controls, indicating COP trace for PTTD tends to be closer to the medial boundary than controls during single-support phase of walking. Conclusion: PTTD patients showed more conservative and cautious postural strategies which may help maintain balance and reduce the need for postural adjustment during PTTD gait. They also showed more medially shifted COP patterns than healthy controls during single-support phase of walking. Dynamic postural control outcomes could be used to develop effective gait training programs aimed at alleviating a medial shift of COP (everted foot) for individuals with PTTD in order to improve their functionality and gait efficiency.

Cortical reorganization to improve dynamic balance control with error amplification feedback

BackgroundError amplification (EA), virtually magnify task errors in visual feedback, is a potential neurocognitive approach to facilitate motor performance. With regional activities and inter-regional connectivity of electroencephalography (EEG), this study investigated underlying cortical mechanisms associated with improvement of postural balance using EA.MethodsEighteen healthy young participants maintained postural stability on a stabilometer, guided by two visual feedbacks (error amplification (EA) vs. real error (RE)), while stabilometer plate movement and scalp EEG were recorded. Plate dynamics, including root mean square (RMS), sample entropy (SampEn), and mean frequency (MF) were used to characterize behavioral strategies. Regional cortical activity and inter-regional connectivity of EEG sub-bands were characterized to infer neural control with relative power and phase-lag index (PLI), respectively.ResultsIn contrast to RE, EA magnified the errors in the visual feedback to twice its size during stabilometer stance. The results showed that EA led to smaller RMS of postural fluctuations with greater SampEn and MF than RE did. Compared with RE, EA altered cortical organizations with greater regional powers in the mid-frontal cluster (theta, 4–7 Hz), occipital cluster (alpha, 8–12 Hz), and left temporal cluster (beta, 13–35 Hz). In terms of the phase-lag index of EEG between electrode pairs, EA significantly reduced long-range prefrontal-parietal and prefrontal-occipital connectivity of the alpha/beta bands, and the right tempo-parietal connectivity of the theta/alpha bands. Alternatively, EA augmented the fronto-centro-parietal connectivity of the theta/alpha bands, along with the right temporo-frontal and temporo-parietal connectivity of the beta band.ConclusionEA alters postural strategies to improve stance stability on a stabilometer with visual feedback, attributable to enhanced error processing and attentional release for target localization. This study provides supporting neural correlates for the use of virtual reality with EA during balance training.

The Effect of Eight Weeks of Water Training on Postural Control and Balance Recovery Strategies in 60-70 Years Old Elderly Men

Background and Aims The risk of falling in people increases with aging. Aquatic exercises create a secure environment for people, and they can reduce the risk of falling among elderly people. This study aimed to investigate the effect of 8 weeks of aquatic exercises on postural control and balance recovery strategies. Methods Thirty elderly people from Kerman province were selected to participate in the research, and they were randomly divided into control (Mean±SD age 63.67±2.58 years, height 169.27±4.74 cm, and weight 71.00±6.95 kg) and intervention groups (Mean±SD age 65.00±3.07 years, height 169.50±27.34 cm, and weight 71.200±4.31 kg). The postural control and balance recovery strategies during sudden movement by treadmill were evaluated using the Biodex and motion analysis system. The intervention group participated in aquatic exercises for 8 weeks (3 times with 45 minutes per week) to challenge the physical and proprioceptive acuity, while the control group lived without any interventions. Data were analyzed using the ANCOVA and Pearson correlation tests (P&lt;0.05). Results The results showed a significant improvement in the scores of postural control and balance recovery strategies (P&lt;0.05). Balance strategies in elderly people moved from the hip toward the ankle (P&lt;0.05). The onset time of muscle activity and the electrical activation of muscles in elders showed significant improvement after participating in this study (P&lt;0.05). Conclusion The results approved that water training has significantly affected the ability to control posture and balance recovery strategies in the elderly and that changing the pattern of muscle activation has increased postural stability and improved balance. It recommends using these exercises in training programs for the elderly to decrease the risk of falls and improve balance.

Effect of Selected Fall-proof Exercises on Fear of Falling and Quality of Life in the Elderly

Objectives: Fear of falling in the elderly can be a disabling disease that causes negative outcomes including reduced daily productivity, reduced physical activities, and lower quality of life. The present study evaluates effects of an 8-week training protocol with selected Fallproof exercises on fear of falling and quality of life in the elderly. Methods &amp; Materials: This is a quasi-experimental study that initiated in 2019. Population of the study includes 53 elderly from nursing homes in Rasht, from among which 24 individuals aged 60-74 were selected using convenience sampling based on inclusion criteria. The subjects were randomly assigned to experimental (n=12; 66.41±4.41 and control n=12; 66.16±2.40) groups. Fallproof exercises include a range of multisensory exercises (visual, vestibular, and somatosensory), center of gravity control, postural strategies, and power training including toe and heel walking, knee flexion and extension, adduction and abduction. Training intensity was increased based on overload principle and individual differences in an 8-week training protocol, three times a week for 60 minutes. Paired t-test and covariance analysis were used for intra-group and inter-group comparisons, respectively. Data analysis was performed using SPSS at significance level of P&lt;0.05. Results: Our results indicate that fear of falling P&lt;0.001 and quality of life P&lt;0.01 improved significantly in the experimental group while showing no differences in the control group. Conclusion: It is concluded that Fallproof exercises significantly improve quality of life and reduce fear of falling in the elderly. This is observed in improvements in the experimental group. Considering multidimensional effects of Fallproof exercises and multifactor nature of fear of falling, these training protocols can be applied in rehabilitation programs in care centers for the elderly.

Muscle-Effort-Minimization-Inspired Kinematic Redundancy Resolution for Replicating Natural Posture of Human Arm.

Replicating natural postures of human arms is essential to generate human-like behaviors in robotic applications for humans nearby. However, how to realize this requirement in interactive scenarios remains a challenge due to the kinematic redundancy and unknown postural control strategy of human arms. Inspired by the physiological characteristics that the musculoskeletal system is coordinated to minimize muscle effort in human behaviors, this paper aims to address the issue by solving a muscle effort minimization problem. It adopts a high-fidelity human arm musculoskeletal model (HAMM) and considers the implicit constraint (desired hand pose) and the inequality constraints (range of joint motion). The constrained minimization is in general nonconvex, consequently sensitive to initial guesses in iterative procedures. So, it is impracticable to solve it directly with existing gradient-based deterministic approaches or standard evolutionary algorithms. As the main contribution, a hybrid inverse kinematics algorithm was proposed for the HAMM with 7 independent and 13 mimic joints to obtain the feasible arm postures satisfying the minimization constraints. Using the arm swivel angle that parametrizes the kinematic redundancy of the HAMM, geometrically equidistant initial guess candidates can be generated over the 1-dimension feasible posture manifold. As another contribution, we present a two-phase global minimization algorithm to handle the nonconvexity of the constrained minimization. It consists of a local-search phase on the null-space of the geometric Jacobian matrix and a global-search phase with an initial guess resampling strategy. The proposed approach was validated by replicating the natural arm postures of 5 right-handed subjects in daily tasks.

Walking with early dinosaurs: appendicular myology of the Late Triassic sauropodomorph Thecodontosaurus antiquus.

Dinosaur evolution is marked by numerous independent shifts from bipedality to quadrupedality. Sauropodomorpha is one of the lineages that transitioned from small bipedal forms to graviportal quadrupeds, with an array of intermediate postural strategies evolving in non-sauropodan sauropodomorphs. This locomotor shift is reflected by multiple modifications of the appendicular skeleton, coupled with a drastic rearrangement of the limb musculature. Here, we describe the osteological correlates of appendicular muscle attachment of the Late Triassic sauropodomorph Thecodontosaurus antiquus from multiple well-preserved specimens and provide the first complete forelimb and hindlimb musculature reconstruction of an early-branching sauropodomorph. Comparisons with other sauropodomorphs and early dinosaurs reveal a unique combination of both plesiomorphic and derived musculoskeletal features. The diversity of appendicular osteological correlates among early dinosaurs and their relevance in muscle reconstruction are discussed. In line with previous evidence, aspects of the limb muscle arrangement, such as conspicuous correlates of lower limb extensors and flexors and low moment arms of hip extensors and flexors, suggest Thecodontosaurus was an agile biped. This reconstruction helps to elucidate the timing of important modifications of the appendicular musculature in the evolution of sauropodomorphs which facilitated the transition to quadrupedalism and contributed to their evolutionary success.

Acute effects of ankle plantar flexor force-matching exercises on postural strategy during single leg standing in healthy adults

BackgroundAnkle plantar flexor force steadiness, assessed by measuring the fluctuation of the force around the submaximal target torque, has been associated with postural stability. Research questionTo investigate whether a force-matching exercise, where submaximal steady torque is maintained at the target torque, can modulate postural strategy immediately. MethodsTwenty-eight healthy young adults performed ankle plantar flexor force-matching exercises at target torques of 5%, 20%, and 50% of maximum voluntary contraction (MVC), in a randomized crossover trial. Participants with their ankle in a neutral position were instructed to maintain isometric contraction at each target torque, as measured by a dynamometer, for 20 s with 3 sets of 5 contractions. Before and after the force-matching exercises, the anterior-posterior velocities and standard deviation of the center of pressure (COP) on the stable platform and the tilt angle of the unstable platform during 20-seconds single-leg standing were measured. The velocities and standard deviations of the COP and tilt angle before and after the exercises were compared using paired t-tests. ResultsThe tilt angle velocity of an unstable platform significantly decreased after the force-matching exercise at a target torque of 5% MVC (p = 0.029), whereas it was unchanged after the exercises at target torques of 20% and 50% MVC. The standard deviations of the tilt angle of unstable platform test did not change significantly after any exercise. Furthermore, no significant differences were observed in the COP velocities or standard deviations on the stable platform test after any exercise. SignificanceOur findings suggest that repeated exertion training at low-intensity contractions can affect postural stability in an unstable condition. Particularly, force-matching exercise at very low-intensity torque, such as 5% of MVC, may be an effective method to improve postural control in the unstable condition, but not in a stable condition.

Effect of pediatric flat foot on the sagittal alignment of the pelvis and spine

Human body segments interact harmoniously and efficiently so that homeostasis is maintained in any circumstances. Even the slightest modification of the support surface can have repercussions on postural control strategies and consequently can lead to a change in the alignment of the whole body. Flat foot is the most common condition of the lower limb. It is clinically manifested on multiple anatomical planes: flattening of the medial longitudinal arch (sagittal plane), valgus of the calcaneus (frontal plane) and abduction of the anterior foot (transverse plane). In any case, the influence of structural modifications of the flat foot on one’s posture, especially in children, still remains an insufficiently researched topic. The purpose of this study was to assess the effects that structural modifications of a flat foot have on the pelvis and spine in the sagittal plane, in children aged 7-9. Thus, the following hypothesis was formulated: the structural modifications of flat feet can modify the sagittal alignment of the pelvis and spine in children aged 7-9. The flat feet were assessed using the Foot Posture Index-6 (FPT-6) while the sagittal alignment of the pelvis and spine was measured using the GPS-400 computerised postural analysis system. Statistical analysis of the data did not indicate any significant correlations between the FPI-6 score and pelvic tilt angle or between the FPI-6 score and differences between the sensors and the lumbar and dorsal spinous processes.

Bilateral vestibulopathy and disabling vertigo: A CARE case series

IntroductionThe term bilateral vestibulopathy (BV) was recently defined by the Bárány Society. Loss of otolith function was not included in their criteria. Although spontaneous progression to complete bilateral impairment of vestibular function is expected, it is unlikely that patients with advanced BV will continue to present episodes of intense vertigo. Here, following CARE case report guidelines, we report the case of patients meeting the criteria for BV and still disabled by vertigo. Case seriesThree patients evaluated in our department meeting the Bárány criteria for definite BV but still complaining of disabling rotatory vertigo were included. All underwent clinical and instrumental vestibular examination. The observations are reported. ConclusionIn case of BV, the conservation of a stable otolithic reference frame could allow patients to optimize postural strategy. It would be useful to revisit a classification of BV by stages, by introducing an evaluation of otolithic function and postural control for possible subsequent vestibular implantation.

Postural control in adolescent boys and girls before the age of peak height velocity: Effects of task difficulty

BackgroundAdolescent children experience a critical developmental period marked by rapid biological changes.Research questionTo describe the longitudinal changes in postural control that occur in adolescent boys and girls before the age of peak height velocity (PHV). MethodsHere, to address the gap of knowledge, we compared the postural control and activation strategies of the muscles that control the ankle joint in twenty-three boys (age 12.5 ± 0.29) and twenty-one girls (age 10.5 ± 0.32). They performed easy (two legs) and difficult (two legs-eyes closed; one leg) postural balance tasks at 18 and 9 months before PHV and at PHV. We quantified the center of pressure (COP) displacements in the anterior-posterior (AP) and mediolateral (ML) directions and electromyographic (EMG) activity of tibialis anterior (TA) and medial gastrocnemius (MG) muscles. ResultsBoys exhibited greater AP and ML COP displacement than girls only for the one leg task (difficult task). Although boys and girls had similar postural control 18 months prior to PHV, girls exhibited lesser COP displacement at 9 months before PHV, which related to greater TA-MG coactivation (R2 = 0.26; p < 0.01). In contrast, postural control was not different between boys and girls with an easy balance task (two legs) performed with eyes open and closed. Rather, we found that all children improved their COP displacement in the ML direction with maturity and both AP and ML COP was significantly lower with eyes open. ConclusionThese findings provide novel evidence that postural control is superior in early adolescent girls than boys 9 months prior to PHV, likely associated with an earlier maturation of muscle coordination.

Effects of Lower-limb Muscle Fatigue, Cardiopulmonary Fatigue, and Brain FatigueTasks on One-legged Landing Motion.

Anterior cruciate ligament (ACL) injury is one of the most frequent sportsinjuries, and previous studies have shown that fatigue is a risk factor for sports injuries.This study aimed to inform prevention of ACL injury by investigating how exercise and desk tasks affect trunk and lower limb alignment and ground reaction force (GRF) during one-legged landing movements. The study subjects were 12 men who performed a one-legged landing movement from a 30-cm platform before and after fatigue tasks, including lower-limb muscle fatigue, cardiopulmonary fatigue, and brain fatigue tasks. For the measurement of joint angles and moments and GRF, a three-dimensional motion analysis device and a floor reaction-force meter were used. Statistics were performed using Wilcoxon's signed rank sum test as a multiple comparison test with Bonferroni adjustment to compare the difference in effects. The maximum trunk flexion angle during landing on one leg was significantly lower in the brain fatigue group than in the control group. The time to peak vertical GRF (pGRF) was significantly shorter in the leg-muscle fatigue group than in the control group. Brain fatigue may have altered the postural strategy before and after landing, resulting in a decrease in trunk flexion angle. Time to pVGRF was shortened in the leg muscle fatigue group, suggesting that there may be an increased risk of ACL injury. Time to pVGRF during lower extremity muscle fatigue and trunk flexion angle during brain fatigue may be more pronounced during actual sports activities.

Modeling and predicting the backstroke to breaststroke turns performance in age-group swimmers

ABSTRACT The purpose of the present study was to identify the performance determinant factors predicting 15-m backstroke-to-breaststroke turning performance using and comparing linear and tree-based machine-learning models. The temporal, kinematic, kinetic and hydrodynamic variables were collected from 18 age-group swimmers (12.08 ± 0.17 yrs) using 23 Qualisys cameras, two tri-axial underwater force plates and inverse dynamics approach. The best models were obtained: (i) with Lasso linear model of the leave-one-out cross-validation in open turn (MSE = 0.011; R2 = 0.825) and in the somersault turn (MSE = 0.016; R2 = 0.734); (ii) the Ridge of the leave-one-out cross-validation (MSE = 0.016; R2 = 0.763) for the bucket turn; and (iii) the AdaBoost tree-based model of the leave-one-out cross-validation for the crossover turn (MSE = 0.016; R2 = 0.644). Model’s selected features revealed that optimum turning performance was very similarly determined for the different techniques, with balanced contributions between turn-in and turn-out variables. As a result, the relevant feature’s contribution of each backstroke-to-breaststroke turning technique are specific; developing approaching speed in conjunction with proper gliding posture and pull-out strategy will result in improved turning performance, and may influence differently the development of specific training intervention programmes.

Strategic alterations of posture are delayed in Parkinson\u2019s disease patients during deep brain stimulation

Parkinson’s disease (PD) is characterized by rigidity, akinesia, postural instability and tremor. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) reduces tremor but the effects on postural instability are inconsistent. Another component of postural control is the postural strategy, traditionally referred to as the ankle or hip strategy, which is determined by the coupling between the joint motions of the body. We aimed to determine whether DBS STN and vision (eyes open vs. eyes closed) affect the postural strategy in PD in quiet stance or during balance perturbations. Linear motion was recorded from the knee, hip, shoulder and head in 10 patients with idiopathic PD with DBS STN (after withdrawal of other anti-PD medication), 25 younger adult controls and 17 older adult controls. Correlation analyses were performed on anterior–posterior linear motion data to determine the coupling between the four positions measured. All participants were asked to stand for a 30 s period of quiet stance and a 200 s period of calf vibration. The 200 s vibration period was subdivided into four 50 s periods to study adaptation between the first vibration period (30–80 s) and the last vibration period (180–230 s). Movement was recorded in patients with PD with DBS ON and DBS OFF, and all participants were investigated with eyes closed and eyes open. DBS settings were randomized and double-blindly programmed. Patients with PD had greater coupling of the body compared to old and young controls during balance perturbations (p ≤ 0.046). Controls adopted a strategy with greater flexibility, particularly using the knee as a point of pivot, whereas patients with PD adopted an ankle strategy, i.e., they used the ankle as the point of pivot. There was higher flexibility in patients with PD with DBS ON and eyes open compared to DBS OFF and eyes closed (p ≤ 0.011). During balance perturbations, controls quickly adopted a new strategy that they retained throughout the test, but patients with PD were slower to adapt. Patients with PD further increased the coupling between segmental movement during balance perturbations with DBS ON but retained a high level of coupling with DBS OFF throughout balance perturbations. The ankle strategy during balance perturbations in patients with PD was most evident with DBS OFF and eyes closed. The increased coupling with balance perturbations implies a mechanism to reduce complexity at a cost of exerting more energy. Strategic alterations of posture were altered by DBS in patients with PD and were delayed. Our findings therefore show that DBS does not fully compensate for disease-related effects on posture.

Proprioceptive postural control strategies differ among non-injured athletes

Postural control during complex tasks requires adequate sensory integration and somaesthetic reweighting: suboptimal postural strategies can lead to injury. We assessed the ability of healthy athletes to reweight somaesthetic signals during postural perturbations on different surfaces. Thirty-five young (16 ± 1 years), healthy, elite handball players participated in this cross-sectional study. Proprioceptive reweighting was evaluated via vibration of the triceps surae and lumbar muscles on firm and foam surfaces. Postural variables and the electromyographic activity of the gluteus medius (GM), semitendinosus (ST) and fibularis longus (FL) were recorded during the PRE (10 s), VIBRATION (20 s) and POST (20 s) periods. Ankle proprioception was predominantly used on the firm compared to foam support. However, two opposing behaviours were observed: a “rigid” strategy in which reliance on ankle proprioception increased on the foam, and a “plastic” strategy that involved a proximal shift of proprioceptive reliance (p < 0.001). The plastic strategy was associated with a more effective recovery of balance after vibration cessation (p < 0.05). ST activation was higher during POST in the rigid strategy and did not return to the PRE level (p < 0.05) whereas it did in the plastic strategy. Proprioceptive strategies for postural control are highly variable and future studies should evaluate their contribution to injury.

Effects of Task Constraints on Kinematic Characteristics of Body Segments in Children with Cerebral Palsy and Children with Typical Development during Hand-Reaching

Background: Children with cerebral palsy (CP) have difficulty in managing postural control during functional reaching tasks, although children with different postural control ability are able to come up with different motor solutions to cope with different task demands. This study examined the effect of task constraint on postural control performance in children with cerebral palsy and typical development (TD) in terms of different postural control abilities. Methods: A cross-sectional research design was used. Twelve children with spastic diplegic cerebral palsy (mean age: 107.8 months) and 16 typically developing children (mean age: 110.9 months) participated in this study. Individually, all subjects were seated in a height-adjusted chair and were requested to reach for target(s) located at three different directions (medial, anterior, and lateral). A six-camera Qualisys Motion Capture System was used to capture motion data. Kinematic data in terms of body alignment and angular changes were analyzed. Results: Children with cerebral palsy demonstrated different postural control strategies to complete different reaching tasks compared to typically developing children by preparing postural alignment in advance, coordinating different body orientation movements during reaching after showing difficulty in managing reach medially. Conclusions: Children with cerebral palsy perceive their insufficient ability and prepare their alignment in advance to adapt to the task demanded and decrease the postural challenges of the task. Even though children with cerebral palsy self-generate different motor solutions to reach without falling, these alternative strategies might not be the most efficient adaptation.