Retracted: Reducing motion artifacts in 4D MR images using principal component analysis (PCA) combined with linear polynomial fitting model.

Altered postural control has been observed in chronic ankle instability (CAI). Kinesiophobia (fear of re-injury) has been identified as a factor influencing postural stability. Therefore, postural control was assessed during jump landing among CAI athletes with and without kinesiophobia, as well as healthy controls. A total of 60 participants were recruited, including 40 individuals with CAI and 20 healthy controls. The CAI group was subdivided into two cohorts: 20 subjects with kinesiophobia (Tampa Scale of Kinesiophobia score > 37) and 20 without kinesiophobia. All participants performed a single-leg jump landing task on a force plate. The following postural stability metrics were calculated: time to stabilization (TTS), and the mean and standard deviation of center of pressure (COP) displacement and velocity in the anterior-posterior (AP), medial-lateral (ML), and total directions. CAI subjects with kinesiophobia exhibited longer TTSs in the AP (p = 0.019), vertical, and total directions (p < 0.001, p = 0.015, p = 0.002) than healthy subjects. Additionally, CAI subjects with kinesiophobia demonstrated a significant increase in the velocity of COP displacement in the AP and ML directions (p < 0.001, p = 0.004). These individuals showed greater variability in the velocity of COP displacement in the AP direction and in COP displacement in the ML direction than healthy subjects (p < 0.001). Also, CAI with kinesiophobia group presented less variability in the velocity of COP displacement in the ML direction than other groups (p < 0.001, p = 0.026). CAI with kinesiophobia group needed more time and more velocity in the AP direction than without kinesiophobia group (p = 0.003). Individuals with a high fear of re-injury may perceive the jump landing task as threatening, requiring more time to land and regain stability. This fear can restrict the variability of velocity in the ML direction, resulting in decreased control over the AP direction due to limitations on managing degrees of freedom.

Four Dimensional Magnetic Resonance Imaging With 3D Radial Sampling and Self-gating Based K-space Sorting: Early Clinical Experience on Pancreatic Cancer Patients

This paper presents an experimental study to investigate how humans interact with a robotic arm simulating primarily unstable, damping-defined, mechanical environments, and to quantify lower bounds of robotic damping that humans can stably interact with. Human subjects performed posture maintenance tasks while a robotic arm simulated a range of negative damping-defined environments and transiently perturbed the human arm to challenge postural stability. Analysis of 2-dimensional kinematic responses in both the time domain and phase space allowed us to evaluate stability of the coupled human-robot system in both anterior-posterior (AP) and medial-lateral (ML) directions, and to determine the lower bounds of robotic damping for stable physical human-robot interaction (pHRI). All subjects demonstrated higher capacity to stabilize their arm against negative damping-defined environments in the AP direction than the ML direction, evidenced by all 3 stability measures used in this study. Further, the lower bound of robotic damping for stable pHRI was more than 3.5 times lower in the AP direction than the ML direction: -30.0 Ns/m and -8.2 Ns/m in the AP and ML directions, respectively. Sensitivity analysis confirmed that the results in this study were relatively insensitive to varying experimental conditions. Outcomes of this study would allow us to design a less conservative robotic impedance controller that utilizes a wide range of robotic damping, including negative damping, and achieves more transparent and agile operations without compromising coupled stability and safety of the human-robot system, and thus improves the overall performance of pHRI.

In this study, we aimed to investigate the acute effects of exercise on postural measures in arthritic patients. We obtained posturographic measurements of 8 women with lower extremity arthritis for 30 s before and after a 60-min aquatic exercise. The center of pressure (COP) was recorded while the volunteers were in an upright position with their eyes open. The time domain measures and the frequency domain measures of the COP time series in the anterior-posterior (AP) and medial-lateral (ML) directions were calculated. In addition, the frequency domain measures were calculated for the COP velocity time series. A paired T-test revealed no significant differences in any time domain measures between pre- and post-exercise; however, there were significant decreases in the 95% power frequency of the COP in the AP direction (0.834 ± 0.296 to 0.627 ± 0.230 Hz, p=0.027) for the frequency domain measures. For the velocity time series, the mean power frequency in both the AP (1.47 ± 0.528 to 1.22 ± 0.360 Hz, p=0.047) and ML (1.28 ± 0.245 to 1.13 ± 0.151 Hz, p=0.022) directions, and the 95% power frequency in the ML direction (3.41 ± 0.653 to 2.96 ± 0.468 Hz, p=0.038) decreased significantly in the post-exercise condition. This study reports that a single session of exercise has a subtle but detectable acute effect on postural balance in arthritic patients.

Monitoring natural human gait in real-life environment is essential in many applications including the quantification of disease progression, and monitoring the effects of treatment and alteration of performance biomarkers in professional sports. Nevertheless, reliable and practical techniques and technologies necessary for continuous real-life monitoring of gait is still not available. This paper explores in detail the correlations between the acceleration of different body segments and walking ground reaction forces GRF(t) in three dimensions and proposes three sensory systems, with one, two, and three inertial measurement units (IMUs), to estimate GRF(t) in the vertical (V), medial-lateral (ML), and anterior-posterior (AP) directions. The nonlinear autoregressive moving average model with exogenous inputs (NARMAX) non-linear system identification method was utilized to identify the optimal location for IMUs on the body for each system. A simple linear model was then proposed to estimate GRF(t) based on the correlation of segmental accelerations with each other. It was found that, for the three-IMU system, the proposed model estimated GRF(t) with average peak-to-peak normalized root mean square error (NRMSE) of 7%, 16%, and 18% in V, AP, and ML directions, respectively. With a simple subject-specific training at the beginning, these errors were reduced to 7%, 13%, and 13% in V, AP, and ML directions, respectively. These results were found favorably comparable with the results of the benchmark NARMAX model, with subject-specific training, with 0% (V), 4% (AP), and 1% (ML) NRMSE difference.

Background and aimThe suspensory strategy, a method for controlling postural balance in the vertical direction of the center of mass (COM), is considered by the elderly as a means of balance control. The vertical COM control might alter the sensory integration and regularity of postural sway, which in turn impacts balance. However, to date, this was not confirmed. Thus, this study aimed at investigating the influence of the suspensory strategy achieved through knee flexion on the static standing balance.MethodsNineteen participants were monitored at knee flexion angles of 0°, 15°, and 65°. Time-frequency analysis and sample entropy were employed to analyze the COM data. Time-frequency analysis was utilized to assess the energy content across various frequency bands and corresponding percentage of energy within each frequency band. The outcomes of time-frequency are hypothesized to reflect the balance-related sensory input and sensory weights. Sample entropy was applied to evaluate the regularity of the COM displacement patterns.ResultsKnee flexion led to a decreased COM height. The highest energy content was observed at 65° knee flexion, in contrast with the lowest energy observed at 0° in both the anterior–posterior (AP) and medial-lateral (ML) directions. Additionally, the ultra-low-frequency band was more pronounced at 65° than that at 0° or 15° in the ML direction. Furthermore, the COM amplitudes were notably higher at 65° than those at 0° and 15° in the AP and ML directions, respectively. The sample entropy values were lower at 65° and 15° than those at 0° in the ML direction, with the lowest value observed at 65° in the vertical direction.ConclusionThe suspensory strategy could enhance the sensory input and cause sensory reweighting, culminating in a more regular balance control. Such suspensory strategy-induced postural control modifications may potentially provide balance benefits for people with declining balance-related sensory, central processing, and musculoskeletal system functions.

Dementia alters standing postural adaptation during a visual search task in older adult men

Intraoperative fluoroscopy shows better agreement and interchangeability in tibial tunnel location during single bundle anterior cruciate ligament reconstruction with postoperative three-dimensional computed tomography compared with an intraoperative image-free navigation system

Introduction: Exercise promotes physiological improvements that reflect better quality of life and survival among chronic kidney disease patients. However, little is known about the effect of exercise on postural control of hemodialysis patients. Objective: To evaluate the effect of intradialytic aerobic exercise on postural balance in patients on hemodialysis. Methods: a pilot study with seven individuals was conducted at the Hemodialysis Center of Bauru State Hospital. The Berg Balance Scale evaluated balance and postural balance was evaluated by the force platform Advance Mechanical Technology Inc. (AMTI - AccuGait). Trunk mean sway amplitude in the anterior-posterior (AP) and medial-lateral (ML) directions and mean velocity in the AP and ML directions were assessed. Secondary outcomes about functional capacity and body composition (DEXA) were evaluated. The aerobic exercise was performed with a ergometric bicycle during the first two hours of hemodialysis session for 50-60 minutes (BORG &gt;12), three times a week for 12-weeks. Results: Four men and three women, 52.86 ± 11.08 years, participated in the study. There was no difference between pre and post-test of postural balance outcomes. Although the results were not statistically significant, except for the lean body mass and leg lean mass, the presented pilot study suggests improved functional balance and lower limb strength. Conclusion: The 12-weeks of aerobic exercise protocol during hemodialysis despite inducing gains in lean body mass and leg lean mass, was not able to promote improvements in postural control of chronic renal failure patients on hemodialysis.

Falling is one of the major public problems to the elderly, resulting in limitations of daily living activities. It can be induced by the functional loss of the balance ability and muscle strength in the elderly. It has been, however, not well investigated to suggest an effective methodology improving the balance ability and muscle strength for the prevention of the falling due to lack of information about the characteristics of the balance and muscle activations responded to the dynamic motions. The aim of the current study is, therefore, to identify the characteristics of the balance and muscle activations responded to the dynamic motions in Anterior-Posterior(AP) and Medial Lateral(ML) directions. For that, a motion capture system with eight infrared cameras, surface electromyogram system and Wii Fit system with a customized variable unstable base were used and kinematic and kinetic data obtained from the systems were analyzed for five healthy male(<TEX>$24.8{\pm}3.3years$</TEX>, <TEX>$177.4{\pm}2.0cm$</TEX>, <TEX>$73.9{\pm}12.9kg$</TEX>, <TEX>$23.5{\pm}4.0kg/m$</TEX>). The results showed that the characteristics of the balance and muscle activations were differently responded to between the dynamic motions in Anterior-Posterior(AP) and Medial Lateral(ML) directions. These findings may indicate that customized dynamic motions should be applied to the training of the balance ability and muscle strength for the effective prevention of the falling. This study may be meaningful to providing basic information to establish a guideline improving effectively the balance ability and muscle strength.

Postural stability during long duration quiet standing in post stroke hemiplegia

Background:Previous research has identified deficient dual-task balance control at thetime of return to play (RTP) and possible worsening after RTP in olderadolescents/young adults with concussion. These findings have not beeninvestigated in younger patients with concussion.Hypothesis/Purpose:We hypothesized that concussed adolescents would have slower walking speedand increased medial-lateral (ML) center of mass (COM) movement, which wouldnormalize by the time of RTP but worsen after resuming activity.Methods:13 adolescent concussion patients (7 male; age 10-17 years) wereprospectively evaluated at their initial visit (IV) (mean 18, range 4-43days post-concussion), at RTP clearance (mean 46, range 12-173 dayspost-concussion), and one month later (mean 26, range 20-41 days post-RTP)along with 11 controls (3 male) seen for similarly timed visits. Standingbalance was assessed using range and root mean squared (RMS) COM motion inthe anterior-posterior (AP) and ML directions during standing on both legswith eyes open while performing quiet standing, dual-task audio Stroop,side-to-side head turns, and side-to-side thumb tracking tasks. Dynamicbalance was assessed using walking speed and COM ML range and velocityduring walking alone and with side-to-side head turns and verbal fluency(reciting words starting with “F”) dual tasks. Patients were comparedagainst controls using t-tests, and changes over time were evaluated usinglinear mixed-effects regression.Results:During standing, patients had higher COM ML RMS than controls at IV duringhead turns and higher COM AP range during thumb tracking. COM ML motiondecreased from IV to RTP (head turns range -6.5mm, p=0.058; head turns RMS-16.8mm, p=0.002; thumb range 9.2mm, p=0.012) and increased from RTP to 1month follow-up (head turns RMS +10.0mm, p=0.040; Stroop RMS +8.4mm,p=0.086).Patients walked slower than controls at IV during all tasks, and COM ML rangewas higher in patients vs. controls during verbal fluency at IV and RTP.Walking speed increased from IV to RTP during verbal fluency (+7.8cm/s,p=0.044), from RTP to post-RTP in single task walking (+6.1cm/s, p=0.041),and at each successive visit during head turns (+6.0cm/s and +6.5cm/s,p<0.07). COM ML range also decreased in patients from IV to RTP withverbal fluency (-14.7mm, p=0.011) and from RTP to post-RTP in single taskwalking ( 4.0mm, p=0.061).Conclusion:Adolescent concussion patients had deficits in static and dynamic balancecontrol at initial presentation. This tended to improve by RTP and onlyworsened post-RTP for dual-task ML control during standing, suggesting thatcurrent conservative treatment protocols are appropriate.

IntroductionExternal continuous perturbations using a motion platform have been developed by employing either sum-of-sines (SoS) or a pseudorandom ternary sequence (PRTS) of numbers to quantify body sway evoked in the medial-lateral (ML) or anterior-posterior (AP) directions, which ultimately helps understand the human postural control system. These stimuli have been provided via pitch tilts of the motion platform for evaluations of AP balance responses or roll tilts for ML balance responses. However, little is known about whether a healthy postural control system responds to 2-dimensional (2D) perturbations similarly when the perturbation stimuli are provided in semicircular canal coordinates (i.e., right-anterior/left-posterior (RALP) and left-anterior/right-posterior (LARP)) versus roll/pitch coordinates. Stimuli provided in either set of coordinates were orthogonal in both time and space. Our 2D platform perturbations provided in RALP/LARP coordinates will have the potential to better assess the contribution of each pair of the vertical semicircular canals to postural control for individuals with dysfunction of the vertical semicircular canals.MethodsTo address this knowledge gap, we developed four different balance perturbation trajectories using sum-of-sines (SoS) signals and simultaneously provided those stimuli in (i) roll and pitch, (ii) RALP and LARP, and (iii) roll, pitch, RALP, and LARP dimensions. Center of pressure (CoP) data were collected from 24 healthy participants (40 13 years of age) on a commercially available motion platform (Virtualis Motion VR, Perault, France). A discrete Fourier transform (DFT) was applied to the CoP data to identify responses at perturbed frequencies (i.e., spectral response components).ResultsWe found that ML and AP postural responses were not significantly different when the platform perturbations were simultaneously provided in RALP/LARP coordinates versus roll/pitch coordinates.DiscussionThis finding suggests that our 2D platform perturbations in RALP/LARP coordinates allow us (1) to compare ML and AP responses evoked by RALP and LARP stimuli to existing literature showing those responses evoked by roll and pitch stimuli and (2) to characterize postural responses for individuals with sensory deficits to better isolate contributions of the vertical semicircular canals to postural control.

Effects of heel height and high-heel experience on foot stability during quiet standing

Dosimetric and isocentric variations due to patient setup errors in CT-based treatment planning for breast cancer by electronic portal imaging