Fractal dimension approach in postural control of subjects with Prader-Willi Syndrome

Overweight in elderly increases postural instability during sit-to-stand test: a Kinect-based assessment

BACKGROUND

Being overweight increases the risk of falls and subsequent injuries. However, conventional functional balance tests may not be appropriate for this population as body weight can affect test performance. Thus, it is crucial to develop reliable methods for assessing balance ability in overweight individuals.

AIM

The purpose of this study was to utilize a portable gaming device (Kinect Xbox 360) to measure the center of mass (CoM) of elderly individuals and compare the results between normal weight and overweight elderly women.

METHODS

The study included 64 female elderly individuals who were divided into two groups: 32 normal weight and 32 overweight subjects, matched for age (matched pairs design). The study collected the body's CoM during the five-time sit-to-stand test (FTSST) using Kinect camera. Additionally, the participants underwent the time up and go test (TUGT) and one-leg standing balance (OLSB) tests. The Kinect Xbox 360 demonstrated high test-retest reliability for measuring body's center of mass sway, with ICC3,1 value of 0.982 in the vertical direction, 0.983 in the mediolateral (ML) direction, and 0.997 in the anteroposterior (AP) direction. Additionally, the technical error of measurement (TEM) was very low at 0.006, 0.002, and 0.004, respectively. The % coefficient of variation ranged from 1.31% to 5.68%, indicating good measurement consistency.

RESULTS

Overweight individuals took longer to complete FTSST and TUGT compared to normal weight individuals, but no significant difference was observed in OLSB tests. Moreover, overweight elderly individuals had greater sway length in the ML and AP directions compared to normal weight elderly individuals.

DISCUSSION AND CONCLUSION

Overweight elderly individuals had poorer balance than their normal weight counterparts when using Kinect camera. The researchers suggest that Kinect device can be a cost-effective alternative to measure balance performance among overweight elderly in the community-based setting.

Nonlinear Measures to Evaluate Upright Postural Stability: A Systematic Review

Conventional biomechanical analyses of human movement have been generally derived from linear mathematics. While these methods can be useful in many situations, they fail to describe the behavior of the human body systems that are predominately nonlinear. For this reason, nonlinear analyses have become more prevalent in recent literature. These analytical techniques are typically investigated using concepts related to variability, stability, complexity, and adaptability. This review aims to investigate the application of nonlinear metrics to assess postural stability. A systematic review was conducted of papers published from 2009 to 2019. Databases searched were PubMed, Google Scholar, Science-Direct and EBSCO. The main inclusion consisted of: Sample entropy, fractal dimension, Lyapunov exponent used as nonlinear measures, and assessment of the variability of the center of pressure during standing using force plate. Following screening, 43 articles out of the initial 1100 were reviewed including 33 articles on sample entropy, 10 articles on fractal dimension, and 4 papers on the Lyapunov exponent. This systematic study shows the reductions in postural regularity related to aging and the disease or injures in the adaptive capabilities of the movement system and how the predictability changes with different task constraints.

The Effect of Cryotherapy Application to the Knee Joint on Dynamic Postural Stability

CONTEXT

Decreased postural balance is a primary risk factor for lower-limb injuries. Cryotherapy is commonly utilized by clinicians to provide local analgesia for minor acute knee joint musculoskeletal injuries during breaks in play or at halftime. Its effect on dynamic postural balance remains unclear.

OBJECTIVE

To investigate the acute effects of a 15-minute knee joint cryotherapy application on dynamic postural balance, as assessed primarily via a clinically oriented outcome measure.

DESIGN

Experimental study.

SETTING

University biomechanics laboratory.

PATIENTS OR PARTICIPANTS

A total of 28 elite-level college male field-sport athletes.

INTERVENTION

Participants were tested on the anterior, posteromedial, and posterolateral reach directions of the Star Excursion Balance Test both before and after a 15-minute knee joint cryotherapy application.

MAIN OUTCOME MEASURE(S)

Normalized reach distances, 3-dimensional knee joint kinematics, sagittal plane hip and ankle joint kinematics, as well as fractal dimension of the center-of-pressure path during the performance of the anterior, posteromedial, and posterolateral reach directions of the Star Excursion Balance Test.

RESULTS

There was a statistically significant decrease in reach distance scores achieved on anterior, posteromedial, and posterolateral directions of the Star Excursion Balance Test from precryotherapy to postcryotherapy (P < .05). None of the decreases in reach distance scores exceeded the reported smallest detectable difference values. No significant differences were observed in hip, knee, or ankle joint kinematics (P > .05). No significant change in fractal dimension was observed for any reach direction following cryotherapy application (P > .05).

CONCLUSIONS

The results of the present study indicate that dynamic postural balance is unlikely to be adversely affected immediately following cryotherapy application to the knee joint.

Balance Control in Obese Subjects during Quiet Stance: A State-of-the Art

Obese individuals are characterized by a reduced balance which has a significant effect on a variety of daily and occupational tasks. The presence of excessive adipose tissue and weight gain could increase the risk of falls; for this reason, obese individuals are at greater risk of falls than normal weight subjects in the presence of postural stress and disturbances. The quality of balance control could be measured with different methods and generally in clinics its integrity is generally assessed using platform stabilometry. The aim of this narrative review is to present an overview on the state of art on balance control in obese individuals during quiet stance. A summary of knowledge about static postural control in obese individuals and its limitations is important clinically, as it could give indications and suggestions to improve and personalize the development of specific clinical programs.

Effect of Rotating Auditory Scene on Postural Control in Normal Subjects, Patients With Bilateral Vestibulopathy, Unilateral, or Bilateral Cochlear Implants

Objective: The aim of this study was to investigate the impact of a rotating sound stimulation on the postural performances in normal subjects, patients with bilateral vestibulopathy (BVP), unilateral (UCI), and bilateral (BCI) cochlear implantees.

Materials and Methods: Sixty-nine adults were included (32 women and 37 men) in a multicenter prospective study. The group included 37 healthy subjects, 10 BVP, 15 UCI, and 7 BCI patients. The average of age was 47 ± 2.0 (range: 23–82). In addition to a complete audiovestibular work up, a dynamic posturography (Multitest Framiral, Grasse) was conducted in silence and with a rotating cocktail party sound delivered by headphone. The center of pressure excursion surface (COPS), sensory preferences, as well as fractal, diffusion, and wavelet analysis of stabilometry were collected.

Results: The rotating sound seemed to influenced balance in all subgroups except in controls. COPS increased with sound in the BVP and BCI groups in closed eyes and sway-referenced condition indicating a destabilizing effect while it decreased in UCI in the same condition suggesting stabilization (p < 0.05, linear mixed model corrected for age, n = 69). BVP had higher proprioceptive preferences, BCI had higher vestibular and visual preferences, and UCI had only higher vestibular preferences than controls. Sensory preferences were not altered by rotating sound.

Conclusions: The rotating sound destabilized BVP and BCI patients with binaural hearing while it stabilized UCI patients with monaural hearing and no sound rotation effect. This difference suggests that binaural auditory cues are exploited in BCI patients for their balance.

Effects of Kinesiology Tape on Non-linear Center of Mass Dispersion During the Y Balance Test

Static taping of the ankle or knee joint is a common method of reducing risk of injury by providing mechanical stability. An alternative taping technique employs kinesiology tape, which has the additional benefit of improving functionality by stimulating proprioception. There is substantial disagreement whether kinesiology tape shows significant differences in proprioception and postural stability as compared to rigid/static tape when applied at the lower limb. The current study investigated the effects of kinesiology tape and static tape during a Y Balance Test on center of mass as an indicator for postural stability. Forty-one individuals, free of injury, performed the Y Balance Test under the three conditions; no tape, kinesiology tape, and static tape applied at the lower limb to the quadriceps, triceps surae and ankle joint. All participants completed the Y Balance Test to determine whether any significant differences could be observed using center of mass movement as a surrogate measure for balance and proprioception. The Minkowski-Bouligand and box-counting fractal dimension analyses were used as measures of the dynamic changes in the center of mass whilst undertaking the Y Balance Test. Statistical analyses included the Kruskal Wallis test to allow for non-normally distributed data and a Bonferroni corrected pairwise T-test as a post hoc test to ascertain pairwise differences between the three taping conditions. Significance was set at 0.05. The fractal analyses of the dynamic changes in center of mass showed significant differences between the control and both the static tape and kinesiology tape groups (p = 0.021 and 0.009, respectively). The current study developed a novel measure of dynamic changes in the center of mass during a set movement that indicated real-time processing effects during a balance task associated with the type of taping used to enhance postural stability.

Advantages and problems of nonlinear methods applied to analyze physiological time signals: human balance control as an example

Physiological processes are regulated by nonlinear dynamical systems. Various nonlinear measures have frequently been used for characterizing the complexity of fractal time signals to detect system features that cannot be derived from linear analyses. We analysed human balance dynamics ranging from simple standing to balancing on one foot with closed eyes to study the inherent methodological problems when applying fractal dimension analysis to real-world signals. Higuchi dimension was used as an example. Choice of measurement and analysis parameters has a distinct influence on the computed dimension. Noise increases the fractional dimension which may be misinterpreted as a higher complexity of the signal. Publications without specifying the parameter setting, or without analysing the noise-sensitivity are not comparable to findings of others and therefore of limited scientific value.

Gait initiation and termination strategies in patients with Prader-Willi syndrome

BACKGROUND

Gait Initiation (GI) is a functional task representing one of the first voluntary destabilizing behaviours observed in the development of a locomotor pattern as the whole body centre of mass transitions from a large to a small base of support. Conversely, Gait Termination (GT) consists in the transition from walking to standing which, in everyday life, is a very common movement. Compared to normal walking, it requires higher control of postural stability. For a safe GT, the forward movement of the body has to be slowed down to achieve a stable upright position. Stability requirements have to be fulfilled for safe GT. In individuals with Prader-Willi syndrome (PWS), excessive body weight negatively affects the movement, such as walking and posture, but there are no experimental studies about GI and GT in these individuals. The aim of this study was to quantitatively characterise the strategy of patients with PWS during GI and GT using parameters obtained by the Center of Pressure (CoP) track.

METHODS

Twelve patients with PWS, 20 obese (OG) and 19 healthy individuals (HG) were tested using a force platform during the GI and GT tasks. CoP plots were divided into different phases, and duration, length and velocity of the CoP trace in these phases were calculated and compared for each task.

RESULTS

As for GI, the results showed a significant reduction of the task duration and lower velocity and CoP length parameters in PWS, compared to OG and HG. In PWS, those parameters were reduced to a higher degree with respect to the OG. During GT, longer durations, similar to OG, were observed in PWS than HG. Velocity is reduced when compared to OG and HG, especially in medio-lateral direction and in the terminal part of GT.

CONCLUSIONS

From these data, GI appears to be a demanding task in most of its sub-phases for PWS individuals, while GT seems to require caution only towards the end of the task. Breaking the cycle of gait into the phases of GI and GT and implementing specific exercises focusing on weight transfer and foot clearance during the transition phase from the steady condition to gait will possibly improve the effectiveness of rehabilitation and fall and injury prevention.

Sex-specific association between obesity and self-reported falls and injuries among community-dwelling Canadians aged 65 years and older

This study investigated the relationship between body mass index (BMI) and falls among community-dwelling elderly. Results indicate that obesity is associated with increased falls and there appears to be a sex-specific difference with obese men at higher risk of falling. Obesity is identified as a risk factor for falls in men.

INTRODUCTION

The prevalence of falls, fall-related injuries, and obesity has increased over the last decade. The objectives of this study were to investigate sex-specific association and dose-response relationship between BMI and falls (and related injuries) among community-dwelling elderly.

METHODS

Our study sample consisted of 15,860 adults aged 65 years or older (6399 men and 9461 women) from the 2008-2009 Canadian Community Health Survey-Healthy Aging (CCHS-HA). Falls, fall-related injuries, and BMI measures were self-reported. For both sex, dose-response curves presenting the relationship between BMI, falls, and fall-related injuries were first examined. Thereafter, multivariate logistic regression analyses were also performed to investigate these relationships after adjustment for potentially confounding variables.

RESULTS

Of women, 21.7 % reported a fall and 16.9 % of men. The dose-response relationship between BMI and prevalence of falls showed that underweight and obese individuals reported falling more than normal and overweight individuals; this being more apparent in men than women. Finally, the dose relationship between BMI and prevalence of fall-related injuries showed that only obese men seem more likely to have sustained a fall-related injury. Results from the multivariate analysis showed that obesity in men was significantly associated with higher odds of falling odds ratio (OR) 1.33 (1.04-1.70) and was not significantly associated with higher odds of fall-related injuries OR 1.10 (0.66-1.84) over a 12-month period compared to normal weight men. For women, obesity was not significantly associated with higher fall prevalence OR 0.99 (0.79-1.25) and fall-related injuries OR 0.71 (0.51-1.00).

CONCLUSION

Obesity is associated with self-reported falls, and there appears to be a sex-specific difference in elderly persons.

Laboratory Measures of Postural Control During the Star Excursion Balance Test After Acute First-Time Lateral Ankle Sprain

CONTEXT

No researchers, to our knowledge, have investigated the immediate postinjury-movement strategies associated with acute first-time lateral ankle sprain (LAS) as quantified by center of pressure (COP) and kinematic analyses during performance of the Star Excursion Balance Test (SEBT).

OBJECTIVE

To analyze the kinematic and COP patterns of a group with acute first-time LAS and a noninjured control group during performance of the SEBT.

DESIGN

Case-control study.

SETTING

University biomechanics laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 81 participants with acute first-time LAS (53 men, 28 women; age = 23.22 ± 4.93 years, height = 1.73 ± 0.09 m, mass = 75.72 ± 13.86 kg) and 19 noninjured controls (15 men, 4 women; age = 22.53 ± 1.68 years, height = 1.74 ± 0.08 m, mass = 71.55 ± 11.31 kg).

INTERVENTION

Participants performed the anterior (ANT), posterolateral (PL), and posteromedial (PM) reach directions of the SEBT.

MAIN OUTCOME MEASURE(S)

We assessed 3-dimensional kinematics of the lower extremity joints and associated fractal dimension (FD) of the COP path during performance of the SEBT.

RESULTS

The LAS group had decreased normalized reach distances in the ANT, PL, and PM directions when compared with the control group on their injured (ANT: 58.16% ± 6.86% versus 64.86% ± 5.99%; PL: 85.64% ± 10.62% versus 101.14% ± 8.39%; PM: 94.89% ± 9.26% versus 107.29 ± 6.02%) and noninjured (ANT: 60.98% ± 6.74% versus 64.76% ± 5.02%; PL: 88.95% ± 11.45% versus 102.36% ± 8.53%; PM: 97.13% ± 8.76% versus 106.62% ± 5.78%) limbs (P < .01). This observation was associated with altered temporal sagittal-plane kinematic profiles throughout each reach attempt and at the point of maximum reach (P < .05). This result was associated with a reduced FD of the COP path for each reach direction on the injured limb only (P < .05).

CONCLUSIONS

Acute first-time LAS was associated with bilateral deficits in postural control, as evidenced by the bilateral reduction in angular displacement of the lower extremity joints and reduced reach distances and FD of the COP path on the injured limb during performance of the SEBT.

Effect of a single session of transcranial direct-current stimulation on balance and spatiotemporal gait variables in children with cerebral palsy: A randomized sham-controlled study

BACKGROUND

Transcranial direct-current stimulation (tDCS) has been widely studied with the aim of enhancing local synaptic efficacy and modulating the electrical activity of the cortex in patients with neurological disorders.

OBJECTIVE

The purpose of the present study was to determine the effect of a single session of tDCS regarding immediate changes in spatiotemporal gait and oscillations of the center of pressure (30 seconds) in children with cerebral palsy (CP).

METHOD

A randomized controlled trial with a blinded evaluator was conducted involving 20 children with CP between six and ten years of age. Gait and balance were evaluated three times: Evaluation 1 (before the stimulation), Evaluation 2 (immediately after stimulation), and Evaluation 3 (20 minutes after the stimulation). The protocol consisted of a 20-minute session of tDCS applied to the primary motor cortex at an intensity of 1 mA. The participants were randomly allocated to two groups: experimental group - anodal stimulation of the primary motor cortex; and control group - placebo transcranial stimulation.

RESULTS

Significant reductions were found in the experimental group regarding oscillations during standing in the anteroposterior and mediolateral directions with eyes open and eyes closed in comparison with the control group (p<0.05). In the intra-group analysis, the experimental group exhibited significant improvements in gait velocity, cadence, and oscillation in the center of pressure during standing (p<0.05). No significant differences were found in the control group among the different evaluations.

CONCLUSION

A single session of tDCS applied to the primary motor cortex promotes positive changes in static balance and gait velocity in children with cerebral palsy.

Gait strategy in genetically obese patients: a 7-year follow up

The aim of this study was to quantitatively evaluate the change in gait and body weight in the long term in patients with Prader-Willi Syndrome (PWS). Eight adults with PWS were evaluated at baseline and after 7 years. During this period patient participated an in- and out-patient rehabilitation programs including nutritional and adapted physical activity interventions. Two different control groups were included: the first group included 14 non-genetically obese patients (OCG: obese control group) and the second group included 10 age-matched healthy individuals (HCG: healthy control group). All groups were quantitatively assessed during walking with 3D-GA. The results at the 7-year follow-up revealed significant weight loss in the PWS group and spatial-temporal changes in gait parameters (velocity, step length and cadence). With regard to the hip joint, there were significant changes in terms of hip position, which is less flexed. Knee flexion-extension showed a reduction of flexion in swing phase and of its excursion. No changes of the ankle position were evident. As for ankle kinetics, we observed in the second session higher values for the peak of ankle power in terminal stance in comparison to the first session. No changes were found in terms of ankle kinetics. The findings demonstrated improvements associated to long-term weight loss, especially in terms of spatial-temporal parameters and at hip level. Our results back the call for early weight loss interventions during childhood, which would allow the development of motor patterns under normal body weight conditions.

Exergaming for balance training of elderly: state of the art and future developments

Fall injuries are responsible for physical dysfunction, significant disability, and loss of independence among elderly. Poor postural control is one of the major risk factors for falling but can be trained in fall prevention programs. These however suffer from low therapy adherence, particularly if prevention is the goal. To provide a fun and motivating training environment for elderly, exercise games, or exergames, have been studied as balance training tools in the past years. The present paper reviews the effects of exergame training programs on postural control of elderly reported so far. Additionally we aim to provide an in-depth discussion of technologies and outcome measures utilized in exergame studies. Thirteen papers were included in the analysis. Most of the reviewed studies reported positive results with respect to improvements in balance ability after a training period, yet few reached significant levels. Outcome measures for quantification of postural control are under continuous dispute and no gold standard is present. Clinical measures used in the studies reviewed are well validated yet only give a global indication of balance ability. Instrumented measures were unable to detect small changes in balance ability as they are mainly based on calculating summary statistics, thereby ignoring the time-varying structure of the signals. Both methods only allow for measuring balance after the exergame intervention program. Current developments in sensor technology allow for accurate registration of movements and rapid analysis of signals. We propose to quantify the time-varying structure of postural control during gameplay using low-cost sensor systems. Continuous monitoring of balance ability leaves the user unaware of the measurements and allows for generating user-specific exergame training programs and feedback, both during one game and in timeframes of weeks or months. This approach is unique and unlocks the as of yet untapped potential of exergames as balance training tools for community dwelling elderly.

Measuring regularity of human postural sway using approximate entropy and sample entropy in patients with Ehlers-Danlos syndrome hypermobility type

Ligament laxity in Ehlers-Danlos syndrome hypermobility type (EDS-HT) patients can influence the intrinsic information about posture and movement and can have a negative effect on the appropriateness of postural reactions. Several measures have been proposed in literature to describe the planar migration of CoP over the base of support, and the most used in clinical field are the CoP excursions in antero-posterior and medio-lateral direction. In recent years a growing number of studies have been designed to explore the complexity of the COP trajectories during quiet standing. We assessed 13 adults with EDS-HT (EDSG) and 20 healthy adults (CG) during static posture, evaluating the CoP using time and frequency domain analysis and entropy analysis (SampEn and ApEn parameters). Higher values of CoP displacements in medio-lateral and anterior-posterior directions for EDSG than CG were found; no differences were observed in CoP frequency. The entropy analysis showed lower value for EDSG than CG, pointing out the needing of EDSG to concentrate more attention on postural control, loosing complexity and reflecting a less automatized postural control.

The fractal dimension approach in posture: a comparison between Down and Prader-Willi syndrome patients

The suitability of new dynamic system analysis was investigated to compare postural control in Prader-Willi syndrome (PWS) and Down syndrome (DS) patients. Time-domain, frequency-domain parameters and fractal dimension (FD) of centre of pressure (CoP) were computed in maintaining normal standing on a force platform in 20 DS and 13 PWS patients, compared to 26 obese (obese control group, OCG) and 20 healthy individuals (healthy control group, HCG). DS and PWS showed greater displacements along both directions and longer sway path (SP) parameter than HCG and OCG, with statistical differences between PWS and DS for anteroposterior displacement and SP. DS used higher frequency strategy when compared to PWS, OCG and HCG. Both DS and PWS were characterised by greater values of FD than OCG and HCG, with higher values in DS. The analyses in frequency domain and of the dynamic nature of CoP suggest that DS patients are characterised by a more complex and irregular signal than PWS patients.