Center Of Mass Displacement Research Articles

Numerical study of single bubble mobility in triangular and deltoid microchannels using the boundary element method

The study of bubbly liquid dynamics in microchannels of unconventional shapes is of great importance for different fields of science and industry. This work investigates the dynamics of the incompressible single bubbles in the slow periodic flow of viscous liquid in a triangular channel with a variable pressure gradient. The numerical approach used in this research is based on the boundary element method (BEM). This method is widely used for solving three-dimensional problems and problems in areas with complex geometry. The influence of the bubble’s initial position relative to the channel centerline on the bubble deformation, the relative velocity of the bubble, and its center of mass displacement in the channel are considered.

Disrupted somatosensory input alters postural control strategies during the Star Excursion Balance Test (SEBT) in healthy people.

Chronic adaptations, including persistent sensorimotor deficits, remain in individuals with a history of ankle instability, resulting in altered postural control strategies during functional tasks such as gait, running, or landing. However, we do not know the contribution of the altered somatosensory input on postural control strategies during a dynamic balance task such as the Star Excursion Balance Test (SEBT). The purpose of this study was to characterize postural control strategies with and without disrupted somatosensory input during a dynamic balance task in people without chronic ankle sprain. This study was a crossover study design. Twenty healthy young adults (10 men, 10 women; age = 23.9 ± 3.0 years, height = 174.2 ± 7.4 cm, mass = 71.2 ± 16.7 kg) performed the posteromedial reach test during the SEBT while standing on the ground and on foam. We measured the maximum reach distance (MRD); joint angles of the ankle, knee, hip, and trunk in the sagittal, frontal, and transverse planes; and position and displacement of the center of mass (COM) and center of pressure (COP) during the posteromedial reach task. The MRD was shorter when standing on the foam than on the ground (p < 0.001). There was a condition by phase interaction for ankle dorsiflexion; tibia internal rotation; and trunk flexion (p < 0.001; p = 0.03; p = 0.01, respectively). The COM and COP were positioned more laterally on the foam (p < 0.001). The COM and COP anterior-posterior displacements were more anterior during the foam condition (p = 0.017). By using a foam pad to disrupt somatosensory information, participants demonstrated altered strategies to control the joint kinematics, COM, and COP, as a function of posteromedial distance. Ankle and trunk movement strategies may influence the posteromedial reach distance. This model may simulate changes that occur with chronic ankle instability.

Evaluation of lung tumor motion in a large sample: Target-related and clinical factors influencing tumor motion based on four-dimensional CT.

Background and purposeWe aimed to analyze the influence of target‐related and clinical factors on lung tumor motion based on four‐dimensional CT (4DCT), and clarify the motion based on subgroups in lung stereotactic body radiation therapy.Materials and methods4DCT image data of 267 tumors from 246 patients were analyzed. The coordinates in the left–right (LR), anterior–posterior (AP), and cranial–caudal (CC) directions of the center of mass (COM) of the gross tumor volumes in 10 phases of 4DCT were measured. The peak‐to‐peak COM displacement in the LR, AP, CC, and 3D directions was calculated. The influence of target‐related and clinical factors on tumor motion was evaluated using multivariate analysis.ResultsThe tumor segment location correlated with the tumor motion in each direction. Tumor size was predictive of tumor motion in the 3D (p = 0.023) and AP directions (p = 0.049). The tumor motion for metastatic tumors was smaller than that for primary tumors in the LR (p = 0.019) and AP directions (p = 0.008). The CC motion for pulmonary surgery recipients (3.8 ± 4.5 mm) was less than that for patients who had not undergone surgery (5.6 ± 5.4 mm), and no significant clinical factor was observed. BSA and BMI were positively correlated with the motion in the CC (p = 0.02) and LR directions (p = 0.002).ConclusionThe tumor segment location was a good predictor of tumor motion. A larger tumor tends to have a smaller motion. Patients with metastatic tumors or those who have undergone pulmonary surgery exhibited smaller and more unpredictable tumor motions, which required individual assessments. Thus, clinical factors can potentially predict tumor motion.

용무도 앞굴러치기 동작의 운동역학적 분석

The purpose of this study is to kinetic analysis of the apgulleochigi motion of Yongmoodo. And the kinematic variables such as the duration time, COM(center of mass) displacement and velocity, the maximum impact force at landing were analyzed. And the following conclusions were drawn. First, the duration time of the apgulleochigi motion of Yongmoodo was 0.42±0.06 s in P1, 0.48±0.06 s in P2, 0.24±0.10 s in P3, and the total time was 1.14±0.16 s. In addition, the time required for each section during apgulleochigi motion of Yongmoodo showed a long duration time in the order of P2, P1, and P3. Second, the left and right displacements of COM of apgulleochigi motion of Yongmoodo were 0.40±0.05 m for E1, 0.39±0.03 m for E2, 0.39±0.08 m for E3, and 0.37±0.07 m for E4. The displacement before and after COM was 0.52±0.28 m for E1, 0.86±0.22 m for E2, 1.44±0.12 m for E3, and 1.86±0.13 m for E4. COM vertical displacement was 0.99±0.03 m for E1, 0.68±0.04 m for E2, 0.55±0.12 m for E3, and 0.31±0.01 m for E4. Third, the COM left and right velocity of apgulleochigi motion of Yongmoodo are -0.03±0.07 m/s for E1, 0.00±0.07 m/s for E2, -0.02±0.18 m/s for E3, and -0.13±0.33 m/s for E4. The velocity before and after COM was 0.69±0.22 m/s for E1, 0.86±0.18 m/s for E2, 1.56±0.52 m/s for E3, and 2.03±0.15 m/s for E4. The COM vertical speed was -0.36±0.15 m/s for E1, -0.89±0.17 m/s for E2, -1.19±0.44 m/s for E3, and -0.03±0.34 m/s for E4. Fourth, in the apgulleochigi motion of Yongmoodo, the maximum impact force generated by the hand closing to the ground was 1.76±0.25 BW. In summary, in the apgulleochigi motion of Yongmoodo, it would be advantageous to increase the duration of P1 and increase the impact speed upon landing in order to minimize the impact. In addition, it is judged that the impact force is reduced as the right arm is closer to the ground before the upper body is lowered and the vertical velocity of the COM is slowed down during an impact.

Analysis of Postural Instability in the Upright Position on Narrow Platforms and the Interactions with Postural Constraints.

Background: Loss of balance is a considerable risk factor for workers while using ladders, because they are required to maintain static postural balance on platforms of a restricted size. This study observed center of mass (CoM) and center of pressure (CoP) behaviors and evaluated the effects of the platform depth (anterior–posterior length) and working postures. Methods: Eleven male participants stood on four platforms with depths ranging from 6 to 15 cm and maintained their positions for 60 s while performing or not performing other tasks (object holding, upward viewing, or both simultaneously). The kinematics were analyzed on the sagittal plane based on the inverse pendulum model. Results: The absolute moving range for the CoP–CoM linearly increased with the decreasing platform depth, and the working postures affected the slopes of the linear fits. The relative range of CoP–CoM displacement on narrow platforms was highly correlated with the subjective sense of instability. Conclusions: Monitoring the CoP is effective for a better understanding and evaluation of static postural balance. This study’s findings contribute to improving the design of work equipment through the use of wider platforms that are robust against the effects of working postures.

중학교 하키 우수선수와 비우수선수의 페널티 스트로크 동작에 대한 운동역학적 비교분석

The purpose of this study was to kinetics comparative analysis on penalty stroke motion of excellent and non-excellent hockey athletes in middle school. This study was concluded as follows. First, there was no significant difference in the time required for the penalty stroke movement of excellent and non-excellent athletes in all phases. Second, there was no significant difference in COM(center of mass) displacement during penalty stroke motions of excellent and non-excellent players. Third, there was no significant difference in COM horizontal velocity during penalty stroke motions of excellent and non-excellent athletes. Fourth, the stick head velocity during the penalty stroke motion of the excellent and non-excellent athletes showed a significant difference at impact, and the excellent athletes were found to be fast (p<.05). Fifth, there was a significant difference in the torsion angle of the trunk during the penalty stroke motion of the excellent and non-excellent athletes in Event 1 (p<.05). Sixth, the maximum torso torsioning angular velocity during penalty stroke motions of excellent and non-excellent athletes showed a significant difference in phase 2, and non-excellent athletes were found to be fast (p<.05). Seventh, the maximum GRF(ground reaction force) in the penalty stroke motion of the excellent and non-excellent athletes showed a significant difference in the forward foot, and the excellent athletes showed great strength (p<.05).

Evaluation of an inertial measurement unit-based approach for determining centre-of-mass movement during non-seated cycling

Instantaneous crank power does not equal total joint power if a rider’s centre of mass (CoM) gains and loses mechanical energy. Thus, estimating CoM motion and the associated energy changes can provide valuable information about the mechanics of cycling. To date, an accurate and precise method for tracking CoM motion during outdoor cycling has not been validated. PurposeTo assess the suitability of using data from a single inertial measurement unit (IMU) secured to the lower back of the rider for estimating CoM motion during non-seated cycling by comparing vertical displacement derived from the IMU to that of an attached marker cluster and to a full-body kinematic estimate of vertical CoM displacement. MethodsIMU and motion capture data were collected synchronously for 10 s while participants (n = 7) cycled on an ergometer in a non-seated posture at six combinations of power output and cadence. A limits-of-agreement analysis, corrected for repeated measures, was performed on the range of vertical displacement between the IMU and the two other measures. A total of 303 crank cycles were analysed. ResultsThere was excellent agreement between the vertical displacement derived from the IMU and the attached marker cluster (accuracy = 1.6 mm, precision = 3.5 mm). Vertical displacement derived from the IMU systematically overestimated the kinematic estimate of whole-body CoM—with errors increasing linearly with displacement. ConclusionWe interpret these findings as evidence that a single IMU secured to the lower back can provide a suitable approach for deriving a cyclist’s CoM displacement when they ride out of the saddle, but only if the linearly increasing overestimation is accounted for.

Spatiotemporal and Kinematic Comparisons Between Anthropometrically Paired Male and Female Soldiers While Walking With Heavy Loads.

Limited work comparing the effect of heavier carried loads (greater than 30 kg) between men and women has attributed observed differences to sex with the possibility that anthropometric differences may have contributed to those discrepancies. With the recent decision permitting women to enter Combat Arms roles, knowledge of sex-based differences in gait response to load carriage is more operationally relevant, as military loads are absolute and not relative to body weight. The purpose of this study was to describe differences in gait parameters at light to heavy loads between anthropometrically similar male and female soldiers. Eight female and 8 male soldiers, frequency-matched (1-to-1) on height (±0.54 cm) and mass (±0.52 kg), walked at 1.34 m∙s-1 for 10-min bouts on a level treadmill while unloaded (BM) and then carrying randomized vest-borne loads of 15, 35, and 55 kg. Spatiotemporal and kinematic data were collected for 30 s after 5 min. Two-way repeated measures analyses of variance were conducted to compare the gait parameter variables between sexes at each load. As load increased, overall, the percent double support increased, step frequency increased, stride length decreased, hip and ankle range of motion (ROM) increased, and vertical center of mass (COM) displacement increased. Sex-based significant differences were observed in knee ROM and mediolateral COM displacement. Among the male participants, knee ROM increased significantly for all loads greater than BM. For mediolateral COM displacement, male remained constant as load increased, whereas female values decreased between BM and 35 kg. Spatiotemporal and kinematic differences in gait parameters were primarily because of increases in load magnitude. The observed sex-related differences with increasing loads suggest that women may require a more stable gait to support the additional load carried.

Effect of jaw clenching on postural adjustments to a predictable external perturbation

This study investigated the effect of jaw clenching on anticipatory postural adjustments (APAs) and reactive postural adjustments (RPAs). Eight healthy adults were exposed to predictable external perturbations with and without submaximal jaw clenching. We recorded the three-dimensional body kinematics, ground reaction forces, and electromyography (EMG) of 12 muscles. EMG onset, integrated EMG, and positions of the center-of-mass (COM) and center-of-pressure (COP) during the anticipatory and reactive phases of postural adjustments were computed and compared for the jaw clenching and control conditions. Jaw clenching resulted in an earlier onset of APAs and a greater amplitude of trunk and lower limb EMG activities in the APAs and RPAs. There were no differences in the COM and COP displacements after the perturbation. Jaw clenching is effective for enhancing APAs and RPAs, although it may not increase postural stability following predictable external perturbation in healthy adults.

Estimation of Human Center of Mass Position through the Inertial Sensors-Based Methods in Postural Tasks: An Accuracy Evaluation.

The estimation of the body’s center of mass (CoM) trajectory is typically obtained using force platforms, or optoelectronic systems (OS), bounding the assessment inside a laboratory setting. The use of magneto-inertial measurement units (MIMUs) allows for more ecological evaluations, and previous studies proposed methods based on either a single sensor or a sensors’ network. In this study, we compared the accuracy of two methods based on MIMUs. Body CoM was estimated during six postural tasks performed by 15 healthy subjects, using data collected by a single sensor on the pelvis (Strapdown Integration Method, SDI), and seven sensors on the pelvis and lower limbs (Biomechanical Model, BM). The accuracy of the two methods was compared in terms of RMSE and estimation of posturographic parameters, using an OS as reference. The RMSE of the SDI was lower in tasks with little or no oscillations, while the BM outperformed in tasks with greater CoM displacement. Moreover, higher correlation coefficients were obtained between the posturographic parameters obtained with the BM and the OS. Our findings showed that the estimation of CoM displacement based on MIMU was reasonably accurate, and the use of the inertial sensors network methods should be preferred to estimate the kinematic parameters.

Torque responses to in-place-perturbations in people with multiple sclerosis

BackgroundAutomatic postural responses are critical to prevent falls after a loss of balance. Although responses have been shown to be delayed in people with multiple sclerosis (PwMS), the degree to which other aspects of these movements are impacted by MS remains unknown. Research QuestionDo responses to in-place support-surface perturbations differ in PwMS compared to neurotypical adults? Are these responses related to a functional measure of postural response performance- center of mass (COM) displacement?. Method52 PwMS and 20 neurotypical, age-matched adults (NA) experienced backward support surface perturbations resulting in forward loss of balance and requiring an in-place response. Center of pressure (COP) and torque were calculated from force plates while center of mass (COM) approximations were collected via motion capture. Primary outcomes were maximal torque production at the foot and its timing, rate, and onset. ResultsPwMS and NA demonstrated no differences in maximal torque production (p = 0.79), timing of maximal torque (p = 0.29), rate of torque development (p = 0.76), or the onset of AP COP movement (p = 0.44). There was a significant negative association between the rate of torque development and forward COM displacement in both groups (Control: r=-0.64, p = 0.002; MS: r=-0.35, p = 0.01). Larger maximal torque production was also associated with smaller COM displacement in PwMS (r=-0.33, p = 0.02). ConclusionTorque profiles in response to backward support surface translations resulting in feet in-place responses were similar in people with mild MS and neurotypical adults. The rate of development and maximal torque were however correlated to functional postural response outcomes. These findings suggest that while not worse in PwMS during in-place perturbations, force-responses seem to be important predictors of the effectiveness of reactive postural control responses.

Smartphone Monitoring of Gait and Balance During Irregular Surface Walking and Obstacle Crossing.

As gait adaptation is vital for successful locomotion, the development of field-based tools to quantify gait in challenging real-world environments are crucial. The aims of this study were to assess the reliability and validity of a smartphone-based gait and balance assessment while walking on unobstructed and obstructed terrains using two phone placements. Furthermore, age-related differences in smartphone-derived gait strategies when navigating different walking conditions and environments were evaluated. By providing a method for evaluating gait in the simulated free-living environment, results of this study can elucidate the strategies young and older adults utilize to navigate obstructed and unobstructed walking paths. A total of 24 young and older adults ambulated indoors and outdoors under three conditions: level walking, irregular surface walking, and obstacle crossing. Android smartphones placed on the body and in a bag computed spatiotemporal gait (i.e., velocity, step time, step length, and cadence) and balance (i.e., center of mass (COM) displacement), with motion capture and video used to validate parameters in the laboratory and free-living environments, respectively. Reliability was evaluated using the intraclass correlation coefficient and validity was evaluated using Pearson's correlation and Bland-Altman analysis. A three-way ANOVA was used to assess outcome measures across group, condition, and environment. Results showed that smartphones were reliable and valid for measuring gait across all conditions, phone placements, and environments (ICC2,1: 0.606–0.965; Pearson's r: 0.72–1.00). Although body and bag placement demonstrated similar results for spatiotemporal parameters, accurate vertical COM displacement could only be obtained from the body placement. Older adults demonstrated a longer step time and lower cadence only during obstacle crossing, when compared to young adults. Furthermore, environmental differences in walking strategy were observed only during irregular surface walking. In particular, participants utilized a faster gait speed and a longer step length in the free-living environment, compared to the laboratory environment. In conclusion, smartphones demonstrate the potential for remote patient monitoring and home health care. Along with being easy-to-use, inexpensive, and portable, smartphones can accurately evaluate gait during both unobstructed and obstructed walking, indoors and outdoors.

Effects of a lower limb muscular fatigue on posture-movement interaction during a lower limb pointing task.

The aim of the present study was to investigate the effects of muscular fatigue on the interaction between posture and movement during a lower limb pointing task. Participants (n = 16), aged 18-30years, kicked a ball toward a target in four conditions of fatigue: No muscular fatigue (NF), fatigue in the kicking (FM) or postural limb (FP) alone, and fatigue in both limbs (FMP). The mean amplitude and speed of the centre of foot pressure (CoP) and centre of mass (CoM) displacements were estimated through a force platform and an optoelectronic system, respectively. In addition, surface electromyography (EMG) of the biceps femoris, rectus femoris, medial gastrocnemius, and peroneus longus was recorded to investigate the anticipatory postural adjustments (APAs). Muscular fatigue yielded a decreased kicking accuracy (p < 0.001) and an increased time to perform the movement (p < 0.001), mainly during the backswing motion. In addition, significant increases in the mean amplitude and speed of the CoP and CoM displacement were found in the anteroposterior (AP) and mediolateral (ML) axes (ps < 0.001), especially when both limbs were fatigued. The EMG analysis confirmed that fatigue modified the way APAs were generated. During fatigue, postural muscle activity increased, but was delayed with respect to movement onset (ps < 0.001). This pattern of response was more consistent when both limbs were fatigued (p < 0.001). The present results suggested an additive effect of fatigue and a functional adaptation and subsequent decrease in the overall variability of APAs, indicating that postural and motor processes are interdependent.

Lower-limb coordination during gait: The effects of age and walking surface

Automatic postural responses are critical to prevent falls after a loss of balance. Although responses have been shown to be delayed in people with multiple sclerosis (PwMS), the degree to which other aspects of these movements are impacted by MS remains unknown.Do responses to in-place support-surface perturbations differ in PwMS compared to neurotypical adults? Are these responses related to a functional measure of postural response performance- center of mass (COM) displacement?.52 PwMS and 20 neurotypical, age-matched adults (NA) experienced backward support surface perturbations resulting in forward loss of balance and requiring an in-place response. Center of pressure (COP) and torque were calculated from force plates while center of mass (COM) approximations were collected via motion capture. Primary outcomes were maximal torque production at the foot and its timing, rate, and onset.PwMS and NA demonstrated no differences in maximal torque production (p = 0.79), timing of maximal torque (p = 0.29), rate of torque development (p = 0.76), or the onset of AP COP movement (p = 0.44). There was a significant negative association between the rate of torque development and forward COM displacement in both groups (Control: r=-0.64, p = 0.002; MS: r=-0.35, p = 0.01). Larger maximal torque production was also associated with smaller COM displacement in PwMS (r=-0.33, p = 0.02).Torque profiles in response to backward support surface translations resulting in feet in-place responses were similar in people with mild MS and neurotypical adults. The rate of development and maximal torque were however correlated to functional postural response outcomes. These findings suggest that while not worse in PwMS during in-place perturbations, force-responses seem to be important predictors of the effectiveness of reactive postural control responses.

Relationship between different methods to measure ankle range of motion in children with idiopathic toe walking

Automatic postural responses are critical to prevent falls after a loss of balance. Although responses have been shown to be delayed in people with multiple sclerosis (PwMS), the degree to which other aspects of these movements are impacted by MS remains unknown.Do responses to in-place support-surface perturbations differ in PwMS compared to neurotypical adults? Are these responses related to a functional measure of postural response performance- center of mass (COM) displacement?.52 PwMS and 20 neurotypical, age-matched adults (NA) experienced backward support surface perturbations resulting in forward loss of balance and requiring an in-place response. Center of pressure (COP) and torque were calculated from force plates while center of mass (COM) approximations were collected via motion capture. Primary outcomes were maximal torque production at the foot and its timing, rate, and onset.PwMS and NA demonstrated no differences in maximal torque production (p = 0.79), timing of maximal torque (p = 0.29), rate of torque development (p = 0.76), or the onset of AP COP movement (p = 0.44). There was a significant negative association between the rate of torque development and forward COM displacement in both groups (Control: r=-0.64, p = 0.002; MS: r=-0.35, p = 0.01). Larger maximal torque production was also associated with smaller COM displacement in PwMS (r=-0.33, p = 0.02).Torque profiles in response to backward support surface translations resulting in feet in-place responses were similar in people with mild MS and neurotypical adults. The rate of development and maximal torque were however correlated to functional postural response outcomes. These findings suggest that while not worse in PwMS during in-place perturbations, force-responses seem to be important predictors of the effectiveness of reactive postural control responses.

Minimal Thrusters Configuration for Simultaneous Orbit Correction and Reaction Wheels Desaturation for GEO Satellite

The paper considers the problem of the optimal thrusters arrangement aboard a geostationary spacecraft. It is necessary to simultaneously ensure orbit correction and reaction wheels desaturation. A formalization for thrusters optimal arrangement problem is proposed. Examples of the minimal thrusters arrangement are given, taking into account the given limitations and requirements both in the case of regular operation and in the case of a possible failure of one of the thrusters. The influence of possible installation errors and the center of mass displacement is taken into account.

The use of hyaluronic acid hydrogel as a tumour bed marker in breast-conserving therapy

PurposeTo evaluate usefulness of hyaluronic acid (HA) hydrogel as a tumour bed marker in breast conserving therapy (BCT). To analyze inter- (Inter-OV) and intraobserver (Intra-OV) variability of contouring boost target volume (CTVboost) in external beam radiotherapy (EBRT). Materials and methodsThirty-two patients in the HA group and 30 patients in the control group with an early stage breast cancer were included in the study. During the surgery 1–3 ml of HA hydrogel was injected into breast to mark the tumour bed for every patient in the HA group. Moreover, surgical clips were placed underneath the lumpectomy cavity. Patients in the control group were marked only by metal markers. Three radiation oncologists delineated CTVboost twice for every patient. Three parameters were calculated to quantify contouring variability: coefficient of variation for volumes (COVV), center of mass displacement (CoMd) and conformity index (CI). ResultsThere were no significant differences between mean values of COVV for HA and control group, neither for Intra-OV (0.14 vs 0.13) nor Inter-OV (0.19 vs 0.18) calculations. The mean CoMd were 6.1 mm and 9.1 mm for Inter-OV calculations and 3.9 mm and 6.4 mm for Intra-OV in the HA and the control group respectively. The mean CI for Intra-OV improved from 0.61 to 0.65 and from 0.47 to 0.56 for Inter-OV in the control and HA group respectively. ConclusionHA hydrogel used as a tumour bed marker improves tumour bed visibility and reduces inter- and intraobserver variability of EBRT boost target volume delineations.

The kinematics and strategies of recovery steps during lateral losses of balance in standing at different perturbation magnitudes in older adults with varying history of falls

BackgroundStep-recovery responses are critical in preventing falls when balance is lost unexpectedly. We investigated the kinematics and strategies of balance recovery in older adults with a varying history of falls.MethodsIn a laboratory study, 51 non-fallers (NFs), 20 one-time fallers (OFs), and 12 recurrent-fallers (RFs) were exposed to random right/left unannounced underfoot perturbations in standing of increasing magnitude. The stepping strategies and kinematics across an increasing magnitude of perturbations and the single- and multiple-step threshold trials, i.e., the lowest perturbation magnitude to evoke single step and multiple steps, respectively, were analyzed. Fall efficacy (FES) and self-reported lower-extremity function were also assessed.ResultsOFs had significantly lower single- and multiple-step threshold levels than NFs; the recovery-step kinematics were similar. Surprisingly, RFs did not differ from NFs in either threshold. The kinematics in the single-step threshold trial in RFs, however, showed a significant delay in step initiation duration, longer step duration, and larger center of mass (CoM) displacement compared with NFs and OFs. In the multiple-step threshold trial, the RFs exhibited larger CoM displacements and longer time to fully recover from balance loss. Interestingly, in the single-stepping trials, 45% of the step-recovery strategies used by RFs were the loaded-leg strategy, about two times more than OFs and NFs (22.5 and 24.2%, respectively). During the multiple-stepping trials, 27.3% of the first-step recovery strategies used by RFs were the loaded-leg strategy about two times more than OFs and NFs (11.9 and 16.4%, respectively), the crossover stepping strategy was the dominated response in all 3 groups (about 50%). In addition, RFs reported a lower low-extremity function compared with NFs, and higher FES in the OFs.ConclusionsRFs had impaired kinematics during both single-step and multiple-step recovery responses which was associated with greater leg dysfunction. OFs and NFs had similar recovery-step kinematics, but OFs were more likely to step at lower perturbation magnitudes suggesting a more “responsive” over-reactive step response related from their higher fear of falling and not due to impaired balance abilities. These data provide insight into how a varying history of falls might affect balance recovery to a lateral postural perturbation.Trial registrationThis study was registered prospectively on November 9th, 2011 at clinicaltrials.gov (NCT01439451).

Spring-like leg dynamics and neuromuscular strategies for hopping on a mini-trampoline in adults and children.

Improved balance control is an often-cited potential benefit for trampoline interventions. However, it is unknown whether the soft, elastic surface of a trampoline elicits different motion and neuromuscular strategies between adults and children. Therefore, the purpose of the study was to evaluate the center-of-mass (COM) dynamics and neuromuscular strategies for hopping on a mini-trampoline in adults and children. Fourteen children aged 7-12years and 15 adults aged 18-35years hopped on a stiff surface and a mini-trampoline. We evaluated the vertical displacement of COM and leg length, as well as the horizontal displacements between hops. We also assessed muscle activation from tibialis anterior, lateral gastrocnemius, biceps femoris, and vastus lateralis during time periods surround landing and estimated fatigue across the hopping cycles. Our results indicated both groups used spring-like leg dynamics to regulate the COM movement while hopping on a mini-trampoline. Children increased horizontal displacements between hops on the mini-trampoline, requiring greater muscle activation during time-periods associated with proprioceptive input. Moreover, children might not have developed the adult-like ability to appropriately adjust muscle pre-activation for feedforward control. Hopping on a mini-trampoline might increase proprioceptive information and postural demand compared to a stiff surface while reducing neuromuscular fatigue.

Personalized Balance and Fall Risk Visualization with Kinect Two.

When we face a super-aging society, there is a drastically increased need for efficient systems in terms of time and cost that can improve rehabilitation standards for the elderly people and other motor-impaired subjects. Human balance ability depends largely on the control of the full body center of mass (CoM), fall risks can be evaluated by estimating the subject-specific CoM displacement over the support polygon relating to the foot tracking. The CoM position is often estimated using what are known as anthropometric tables in biomechanics field. However, the parameters have been obtained from a standard population and will differ between subjects. Current existing fall risk assessment usually relies on the generic anthropometric table or need the center of pressure (CoP) recordings which are to be evaluated for the risk of fall. CoP measurements require force platform, wii board or specialized shoes, which limits the practical usage in the daily life environment. This work represents a personalized measure of balance that considers subject-specific body mass variations along with the motion tracking by Kinect Two. Based on our previous developments, we firstly verified the system with Kinect Two recording, and with adaptive support polygon extraction process, it realizes a real-time system for evaluating the personalized balance and fall risk visualization for unknown disturbance without needing force platform.