Exercise-induced muscle fatigue in the unaffected knee joint and its influence on postural control and lower limb kinematics in stroke patients

This study aimed to investigate the effects of exercise-induced muscle fatigue in the unaffected knee joint on postural control and kinematic changes in stroke patients. Forty participants（20 stroke patients, 20 age-matched healthy participants） were recruited. To induce fatigue, maximum voluntary isometric contractions were performed in the unaffected knee joint in a Leg Extension Rehab exercise machine using the pneumatic resistance. We measured static and dynamic balance and lower-limb kinematics during gait. Changes in postural control parameters anteroposterior sway speed and total center of pressure distance differed significantly between the stroke and control groups. In addition, changes in gait kinematic parameters knee and ankle angles of initial contact differed significantly between stroke（paretic and non-paretic） and control groups. Muscle fatigue in the unaffected knee and ankle impaired postural control and debilitates kinematic movement of ipsilateral and contralateral lower limbs, and may place the fatigued stroke patients at greater risk for falls.

Effect of suspension training on neuromuscular function, postural control, and knee kinematics in anterior cruciate ligament reconstruction patients

BACKGROUND Suspension training(SET)is a method of neuromuscular training that enables the body to carry out active training under unstable support through a suspension therapy system.However,there have been few reports in the literature on the application of SET to anterior cruciate ligament reconstruction(ACLR)patients.It is not clear what aspects of the patient's function are improved after SET.AIM To investigate the effect of SET on the neuromuscular function,postural control,and knee kinematics of patients after ACLR surgery.METHODS Forty participants were randomized to an SET group or a control group.The SET group subjects participated in a SET protocol over 6 wk.The control group subjects participated in a traditional training protocol over 6 wk.Isokinetic muscle strength of the quadriceps and hamstrings,static and dynamic posture stability test,and relative translation of the injured knee were assessed before and after training.RESULTS The relative peak torque of the quadriceps and hamstrings in both groups increased significantly(P<0.001),and the SET group increased by a higher percentage than those in the control group(quadriceps:P=0.004;hamstrings:P=0.011).After training,both groups showed significant improvements in static and dynamic posture stability(P<0.01),and the SET group had a greater change than the control group(P<0.05).No significant improvement on the relative translation of the injured knee was observed after training in either group(P>0.05).CONCLUSION Our findings show that SET promotes great responses in quadriceps and hamstring muscle strength and balance function in ACLR patients.

Effect of biophysical interventions on balance and postural control in patients with ankle instability:A systematic review

Ankle sprains have been one of the most prevalent injuries in active populations.This study aims to summarize the evidence of the effect of the biophysical techniques on balance and postural control in patients with ankle instability,and provide an overview of the application of biophysical interventions in patients with chronic ankle instability(CAI).A systematic search was conducted to include ten articles from 1989 to 2022 in this study.These articles were classified into two categories of balance and postural control.The authors identified a total of 1267 papers and decided to include 10 of them in the systematic review.The Star Excursion Balance Test(SEBT)technique can help clinicians identify balance deficits and postural control,including a comprehensive evaluation of joint stability,strength,and sensorimotor function that would be undetected with single-leg stance static tests.These ten studies involved 481 participants with a mean age of 25.5±6.3 years.The mean duration time of the interventions was 5.4±2.4 weeks and the mean session training duration time was 36.7±17.0 min.The Kinesio taping(KT)and both the soft and semi-rigid orthosis brace may be productive in enhancing dynamic balance assessed by Star Excursion Balance Test.The use of SG may improve perceived ankle instability and dynamic postural control(i.e.,anterior reach during SEBT)of patients with CAI.Regarding the intervention group,no homogeneity results in uncertainties about which techniques of intervention affect balance and postural control.

Comparison of postural control between healthy subjects and individuals with nonspecific low back pain during exposure to visual stimulus

Background Low back pain （LBP） is a common clinical problem.Many researchers have demonstrated that LBP disorders have difference in sensory strategies for postural control.Optokinetic stimulation （OKS） of optic flow has been widely applied to study its effect on vision,but has not been applied to LBP.Here we used OKS on different surfaces to investigate the characteristics of chronic nonspecific LBP （CNLBP） posture control,so as to provide new theoretical and experimental data for further recognizing CNLBP and enriching its treatment.Methods Fifteen individuals with CNLBP （age range 25-40 years） and 15 age and gender-matched control subjects were recruited.Each subject,while standing on a stable or soft surface,was exposed to random-dot patterns projected on a large screen,with the dots displaying expansion （＋） and contraction （-） and velocities including 80°,40°,and 20° per second.The visual stimulus used a ＂stimuli-interval＂ pattern.The peak velocity,different phases＇ standard deviation （SD） of the anterior-posterior centre of pressure （COP） displacements and the total length of the medial-lateral COP sway （LML） for stable surface and soft surface were recorded by force platform.Results The main effect of surface on all parameters was significant,while the main effect of group and OKS showed no significance with the exception of peak velocity （F（3,95）=3.6,P=0.01） and A2 （F（5,140）=9.34,P ＜0.01） for which the effect of OKS was significant.The interactions of group by OKS of A2 （F（5,140）=3.65,P ＜0.01） and group by surface by OKS （F（5,140）=2.83,P=-0.02）,and surface by OKS of A1 and A3 （P ＜0.05） were significant.It was reported that significantly more SD in amplitude in the T2 phase was seen in persons with CNLBP when confronting the ＋ 40 stimuli on the soft surface （P ＜0.05） compared to healthy individuals.Conclusions There was no significance between persons with CNLBP and healthy people when using the stable surface.Subjects with LBP showed decreased efficiency of postural adjustment when exposed to more complicated tasks and environments,especially OKS in the expansion direction,and displayed a visual-dependent phenomenon.This result suggested that the treatment of abnormal motor patterns in people with LBP should take the properties of task and environment into account.

Diurnal changes in postural control in normal children: Computerized static and dynamic assessments

Mild traumatic brain injury (mTBI) causes postural control deficits and accordingly comparison of aberrant postural control against normal postural control may help diagnose mTBI. However, in the current literature, little is known regarding the normal pattern of postural control in young children. This study was therefore conducted as an effort to fill this knowledge gap. Eight normal school-aged children participated. Posture assessment was conducted before (7-8 a.m. in the morning) and after (4-7 p.m. in the after-noon) school on regular school days using the Balance Master? evaluation system composed of 3 static tests and 2 dynamic balance tests. A significant difference in the weight-bearing squats was detected between morning hours and afternoon hours (P < 0.05). By end of afternoon, the body weight was borne mainly on the left side with the knee fully extended and at various degrees of knee flexion. A significantly better directional control of the lateral rhythmic weight shifts was observed at the end of the afternoon than at morning hours (P < 0.05). In summary, most of our findings are inconsistent with results from previous studies in adults, sug-gesting age-related differences in posture control in humans. On a regular school day, the capacity of postural control and laterality or medio-lateral balance in children varies between morning and afternoon hours. We suggest that posturographic assessment in children, either in normal (e.g., physical education and sports training) or in abnormal conditions (e.g., mTBI-associated balance disorders), be better performed late in the afternoon.

Relationship of proprioception,cutaneous sensitivity,and muscle strength with the balance control among older adults

Background:Balance impairment is one of the strongest risk factors for falls.Proprioception,cutaneous sensitivity,and muscle strength are 3 important contributors to balance control in older adults.The relationship that dynamic and static balance control has to proprioception,cutaneous sensitivity,and muscle strength is still unclear.This study was performed to investigate the relationship these contributors have to dynamic and static balance control.Methods:A total of 164 older adults(female=89,left dominant=15,age:73.5±7.8 years,height:161.6±7.1 cm,weight:63.7±8.9 kg,mean±SD)participated in this study.It tested the proprioception of their knee flexion/extension and ankle dorsi/plantarflexion,along with cutaneous sensitivity at the great toe,first and fifth metatarsals,arch,and heel,and the muscle strength of their ankle dorsi/plantarflexion and hip abduction.The Berg Balance Scale(BBS)and the root mean square(RMS)of the center of pressure(CoP)were collected as indications of dynamic and static balance control.A partial correlation was used to determine the relationship between the measured outcomes variables(BBS and CoPRMS)and the proprioception,cutaneous sensitivity,and muscle strength variables.Results:Proprioception of ankle plantarflexion(r=-0.306,p=0.002)and dorsiflexion(r=-0.217,p=0.030),and muscle strength of ankle plantarflexion(r=0.275,p=0.004),dorsiflexion(r=0.369,p<0.001),and hip abduction(r=0.342,p<0.001)were weakly to moderately correlated with BBS.Proprioception of ankle dorsiflexion(r=0.218,p=0.020)and cutaneous sensitivity at the great toe(r=0.231,p=0.041)and arch(r=0.285,p=0.002)were weakly correlated with CoP-RMS in the anteroposterior direction.Proprioception of ankle dorsiflexion(r=0.220,p=0.035),knee flexion(r=0.308,p=0.001)and extension(r=0.193,p=0.040),and cutaneous sensitivity at the arch(r=0.206,p=0.028)were weakly to moderately correlated with CoP-RMS in the mediolateral direction.Conclusion:There is a weak-to-moderate relationship between proprioception and dynamic and static balance control,a weak relationship between cutaneous sensitivity and static balance control,and a weak-to-moderate relationship between muscle strength and dynamic balance control.

MODELING AND CONTROLLING OF PARALLEL MANIPULATOR JOINT DRIVEN BY PNEUMATIC MUSCLES

A parallel manipulator joint driven by three pneumatic muscles and its posture control strategy are presented. Based on geometric constraints and dynamics, a system model is developed through which some influences on dynamic response and open-loop gain are analyzed including the supply pressure, the initial pressure and the volume of pneumatic muscle. A sliding-mode controller with a nonlinear switching function is applied to control posture, which adopts the combination of a main method that separates control of each muscle and an auxiliary method that postures error evaluation of multiple muscles, especially adopting the segmented and intelligent adjustments of sliding-mode parameters to fit different expected postures and initial states. Experimental results show that this control strategy not only amounts to the steady-state error of 0. 1° without overshoot, but also achieves good trajectory tracking.

A New Posture of International Arms Control and Disarmament

About one year on,international arms control and disarmament appeared to be rebounding to become an issue of great international attention,paralleling the issues of financial crisis and climate change.International nuclear disarmament re-dawned with high profile readjustments by the United States in its nuclear arms control policy and tactics.The US and Russia signed a new agreement of bilateral nuclear disarmament.Multilateral nuclear arms control has also softened,and the nuclear security issue loomed large.The Conference on the Review of Nuclear Non-proliferation was held,the main illustration of the adjustment by the US to its arms control policy and tactics.On balance,however,the US arms control and disarmament policies remain largely rhetorical,as its two strategic objectives of nuclear weapon policy--nuclear deterrence and non-proliferation--has been kept intact,and even intensified.

Effects of contact/collision sport history on gait in early-to mid-adulthood

Background:To determine the effect of contact/collision sport participation on measures of single-task(ST)and dual-task(DT)gait among early-to middle-aged adults.Methods:The study recruited 113 adults(34.88±11.80 years,(mean±SD);53.0%female)representing 4 groups.Groups included(a)former non-contact/collision athletes and non-athletes who are not physically active(n=28);(b)former non-contact/collision athletes who are physically active(n=29);(c)former contact/collision sport athletes who participated in high-risk sports and are physically active(n=29);and(d)former rugby players with prolonged repetitive head impact exposure history who are physically active(n=27).Gait parameters were collected using inertial measurement units during ST and DT gait.DT cost was calculated for all gait parameters(double support,gait speed,and stride length).Groups were compared first using one-way analysis of covariance.Then a multiple regression was performed for participants in the highrisk sport athletes and repetitive head impact exposure athletes groups only to predict gait outcomes from contact/collision sport career duration.Results:There were no significant differences between groups on any ST,DT,or DT cost outcomes(p>0.05).Contact/collision sport duration did not predict any ST,DT,or DT cost gait outcomes.Conclusion:Years and history of contact/collision sport participation does not appear to negatively affect or predict neurobehavioral function in early-to mid-adulthood among physically active individuals.

Multisensory Conflict Impairs Cortico-Muscular Network Connectivity and Postural Stability: Insights from Partial Directed Coherence Analysis

Sensory conflict impacts postural control,yet its effect on cortico-muscular interaction remains underexplored.We aimed to investigate sensory conflict's influence on the cortico-muscular network and postural stability.We used a rotating platform and virtual reality to present subjects with congruent and incongruent sensory input,recorded EEG(electroencephalogram)and EMG(electromyogram)data,and constructed a directed connectivity network.The results suggest that,compared to sensory congruence,during sensory conflict:(1)connectivity among the sensorimotor,visual,and posterior parietal cortex generally decreases,(2)cortical control over the muscles is weakened,(3)feedback from muscles to the cortex is strengthened,and(4)the range of body sway increases and its complexity decreases.These results underline the intricate effects of sensory conflict on cortico-muscular networks.During the sensory conflict,the brain adaptively decreases the integration of conflicting information.Without this integrated information,cortical control over muscles may be lessened,whereas the muscle feedback may be enhanced in compensation.

Differences in standing balance between patients with diplegic and hemiplegic cerebral palsy

Maintaining standing postural balance is important for walking and handling abilities in patients with cerebral palsy. This study included 23 patients with cerebral palsy （seven with spastic diplegia and 16 with spastic hemiplegia）, aged from 7 to 16 years of age. Standing posture balance measurements were performed using an AMTI model OR6-7 force platform with the eyes open and closed. Patients with diplegic cerebral palsy exhibited greater center of pressure displacement areas with the eyes open and greater center of pressure sway in the medial-lateral direction with the eyes open and closed compared with hemiplegic patients, Thus, diplegic patients exhibited weaker postural balance control ability and less standing stability compared with hemiplegic cerebral palsy patients.

Corticospinal activity during a single-leg stance in people with chronic ankle instability

Purpose:The aim of the study was to determine whether corticospinal excitability and inhibition of the tibialis anterior during single-leg standing differs among individuals with chronic ankle instability(CAI),lateral ankle sprain copers,and healthy controls.Methods:Twenty-three participants with CAI,23 lateral ankle sprain copers,and 24 healthy control participants volunteered.Active motor threshold(AMT),normalized motor-evoked potential(MEP),and cortical silent period(CSP)were evaluated by transcranial magnetic stimulation while participants performed a single-leg standing task.Results:Participants with CAI had significantly longer CSP at 100%of AMT and lower normalized MEP at 120%of AMT compared to lateral ankle sprain copers(CSP100%:p=0.003;MEP120%:p=0.044)and controls(CSP100%:p=0.041;MEP120%:p=0.006).Conclusion:This investigation demonstrate altered corticospinal excitability and inhibition of the tibialis anterior during single-leg standing in participants with CAI.Further research is needed to examine the effects of corticospinal maladaptations to motor control of the tibial anterior on postural control performance in those with CAI.

Applications and research trends of digital human models in the manufacturing industry

Virtual reality(VR)has been widely used in various manufacturing industries,and VR-based virtual manufacturing has received significant attention in the current intelligent manufacturing era.Digital human models(DHMs)are essential for virtual manufacturing applications.Additionally,researching new applications of DHMs has developed into an important academic research field.This paper aims to identify the applications and research trends of DHMs in the manufacturing industry and to provide a reference for the continued development of virtual manufacturing and DHMs.We selected a total of 49 related articles from a large number of articles published between 2014 and 2019.The applications of DHMs in the manufacturing industry are analyzed from different perspectives and various relevant technical limitations are discussed.The results indicate that the applications of DHMs differ significantly between different types of fields.The automotive industry is the main application field for DHMs,and assembly/maintenance simulations and evaluations are the main application types.Additionally,there are still some limitations in the establishment of virtual environments,motion control,and DHM evaluation that should be addressed.Finally,research trends in the application of DHMs are illustrated and discussed,including the planning and assessment of human-robot collaboration systems,the combination of DHMs and augmented reality,and improved motion planning for DHMs.In summary,the application of DHMs can improve the realism and effectiveness of virtual manufacturing,and DHMs will be more widely and deeply studied and applied in various manufacturing industries in the near future.

Reactive Response of Older Tennis Practitioners and Healthy Young People in Relation to Balance Perturbations

Background Improving balance control in older adults is one of the main objectives of fall prevention programs,and tennis could represent a promising way to train balance control.Objective To verify whether older tennis players have similar reactive response characteristics to balance perturbations to those of healthy young people.Methods Fifteen young people(23.00±1.96 years)and twelve older people(69.08±3.82 years),remained in an orthostatic position,with their arms at their sides,on a force platform during ten mediolateral perturbations.The surface electromyo-graphy signal of the gluteus maximus,tibialis anterior,gastrocnemius lateralis,and vastus lateralis muscles was acquired on the dominant side.Results The velocity and amplitude parameters of the center of pressure displacement were similar between the groups,as well as the amplitude of the electromyography signal of the tibialis anterior,vastus lateralis,and gastrocnemius lateralis muscles.There was a statistical difference between the groups in the gluteus maximus muscle in the first perturbation.Conclusions Older tennis players present similar center of pressure velocity performance and amplitude of center of pres-sure displacement behavior to young people.Older tennis players have an increased range of muscle activation,generating automatic postural responses adapted to deal with situations of balance perturbations.

Development of a Bionic Hexapod Robot for Walking on Unstructured Terrain

This paper reports the design methodology and control strategy in the development of a novel hexapod robot HITCR-II that is suitable for walking on unstructured terrain. First, the entire sensor system is designed to equip the robot with the perception of external environment and its internal states. The structure parameters are optimized for improving the dexterity of the robot. Second, a foot-force distribution model and a compensation model are built to achieve posture control. The two models are capable of effectively improving the stability of hexapod walking on unstructured terrain. Finally, the Posture Control strategy based on Force Distribution and Compensation （PCFDC） is applied to the HITCR-II hexapod robot. The experimental results show that the robot can effectively restrain the vibration of trunk and keep stable while walking and crossing over the un- structured terrains.