Center Of Pressure Position Research Articles

POSTURAL CONTROL DURING MOTOR DUAL-TASK IN YOUNG ADULTS WITH DIFFERENT LEVELS OF PHYSICAL ACTIVITY

Introduction: Center of pressure (CoP) is an objective measure to assess postural control. A higher displacement of the CoP position can express a decline in postural control. Previous studies have demonstrated that a sedentary lifestyle affects balance negatively and increases the risk of falling. In addition, most activities of daily living involve performing two or more tasks concurrently. Thus, while performing a dual or multi-tasks, it is essential to maintain an adequate postural control to prevent the risk of falls and injuries. Objective: The main goal of this study was to compare the center of pressure displacement between healthy young adults with different levels of physical activity during motor dual-task performance. Method: After checking eligibility criteria, 35 healthy young adults (23.09 ± 3.97 years, mean ± SD) were recruited to perform a motor dual-task: maintaining quiet upright standing posture while performing a concurrent motor task – answer the smartphone, during 60 s. The total excursion of the center of pressure (TOTEX_CoP), the displacement anterior-posterior (CoP-AP), and medial-lateral (CoP-ML) of the center of pressure were recorded by Bertec® force plate, and the data was assessed with a Matlab routine. To analyze center of pressure excursions in different levels of physical activity, the International Physical Activity Questionnaire (IPAQ) – short version was used to assess physical activity levels. Then, the participants were divided into three groups: sedentary (n=5), minimally active (n=13), and highly active (n=17). Statistical analyses were performed using IBM-SPSS (version 25.0). To compare center of pressure displacement between different levels of physical activity during motor dual-task was used the Kruskal-Wallis test. The significance level was set at p < 0.05, and the data were shown as the median and interquartile range (IQR). Results: A tendency for a higher total displacement of the center of pressure was observed in the sedentary group (TOTEX_CoP: 3110.67 (2466.54-3908.73) mm) compared to the physically active groups (minimally active - TOTEX_CoP: 2600.75 (2500.34-3205.97) mm; highly active - TOTEX_CoP: 2712.99 (2499.01-3275.84) mm), but differences were not statistically significant between the three groups (p > 0.05). The same happened in the anteroposterior and mediolateral center of pressure displacement (p > 0.05). Conclusions: Physically active young adults did not present less postural oscillation than sedentary young adults during motor dual-task performance. The small sample in each physical activity group could have contributed to the lack of statistical significance. Therefore, we suggest more studies that assess the influence of the level of physical activity on postural control.

Understanding Modulation of Ankle Stiffness During Stance Phase of Walking on Different Ground Surfaces

Understanding how human ankle mechanics are modulated when walking on various ground surfaces (e.g., soft and unstable ground surfaces) would help the development of controllers of lower extremity robots (e.g., prostheses and exoskeletons) mimicking human ankle behaviors. With this goal in mind, this study investigated how ankle stiffness in the sagittal plane is modulated throughout the stance phase of walking over different ground surfaces. A robotic platform, capable of simulating different mechanical environments, was used to quantify ankle stiffness in the sagittal plane during walking over compliant and rigid surfaces. The group average results of 10 healthy individuals showed that ankle stiffness increased with the progression of stance phase of walking but there was no significant environmental effect on the stiffness modulation. Further investigation into each individual subject revealed that surface compliance had an impact on the modulation of ankle stiffness in the later stance phase, which was significantly correlated with center of pressure position regardless of the surface condition (Pearson correlation coefficient: ∼0.93). Implications of the observed results for the development of continuous impedance controllers for lower extremity robots are discussed.

Design of pediatric robot to simulate infant biomechanics for neuro-developmental assessment in a sensorized gym.

Infants at risk for developmental delays often exhibit postures and movements that may provide a window into potential impairment for cerebral palsy and other neuromotor conditions. We developed a simple 4 DOF robot pediatric simulator to help provide insight into how infant kinematic movements may affect the center of pressure (COP), a common measure thought to be sensitive to neuromotor delay when assessed from supine infants at play. We conducted two experiments: 1) we compared changes in COP caused by limb movements to a human infant and 2) we determined if we could predict COP position due to limb movements using simulator kinematic pose retrieved from video and a sensorized mat. Our results indicate that the limb movements alone were not sufficient to mimic the COP in a human infant. In addition, we show that given a robot simulator and a simple camera, we can predict COP measured by a force sensing mat. Future directions suggest a more complex robot is needed such as one that may include trunk DOF.

Evaluation of the Foot Center of Pressure Estimation from Pressure Insoles during Sidestep Cuts, Runs and Walks.

Estimating the foot center of pressure (CoP) position by pressure insoles appears to be an interesting technical solution to perform motion analysis beyond the force platforms surface area. The aim of this study was to estimate the CoP position from Moticon pressure insoles during sidestep cuts, runs and walks. The CoP positions assessed from force platform data and from pressure insole data were compared. One calibration trial performed on the force platforms was used to localize the insoles in the reference coordinate system. The most accurate results were obtained when the motion performed during the calibration trial was similar to the motion under study. In such a case, mean accuracy of CoP position have been evaluated to mm along anteroposterior (AP) axis and mm along mediolateral (ML) axis for sidestep cuts, mm along AP axis and mm along ML axis for runs, mm along AP axis and mm along ML axis for walks. The accuracy of the CoP position assesment from pressure insole data increased with the vertical force applied to the pressure insole and with the number of pressure cells involved.

The center of pressure position in combination with ankle dorsiflexion and trunk flexion is useful in predicting the contribution of the knee extensor moment during double-leg squatting

BackgroundSquatting exercises are commonly used in rehabilitation for knee joint disorders; in these exercises, control of knee extensor moment is important to enhance training effects and to avoid adverse effects. Ankle dorsiflexion and trunk flexion are widely used to reduce knee extensor moments during squatting, but the increased load on the low back is a concern. The purpose of this study was to determine whether the anterior–posterior (AP) center-of-pressure (COP) position and the AP-COP position in combination with ankle dorsiflexion and trunk flexion angles can predict the contribution of the knee extensor moment during double-leg squatting.MethodsTwenty-eight healthy individuals (14 female and 14 male participants, age 22.8 ± 1.3 years) performed three sets of five consecutive double-leg squats. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system with force plates. Univariate and multivariate regression analyses were performed to predict the contribution of the knee extensor moment (% total support moment) from AP-COP position, ankle dorsiflexion, and trunk flexion.ResultsThe AP-COP position was a significant predictor of the knee extensor moment contribution (R2 = 0.168, P = 0.030). Multivariate analysis showed that the ankle dorsiflexion angle (ΔR2 = 0.561, β = 0.842) and AP-COP position (ΔR2 = 0.296, β = − 0.499) predicted the knee extensor moment contribution (model R2 = 0.857, P < 0.001). Additionally, the combination of trunk flexion (ΔR2 = 0.429, β = − 0.613) and AP-COP position (ΔR2 = 0.109, β = − 0.332) predicted the knee extensor moment contribution (model R2 = 0.538, P < 0.001). The limb symmetry index of the knee extensor moment was significantly associated with that of the AP-COP position (R2 = 0.493, P < 0.001) but not with that of the ankle dorsiflexion angle (P = 0.057).ConclusionsThe AP-COP position can predict the contribution of the knee extensor moment and improve the prediction when combined with ankle dorsiflexion and trunk flexion. The present findings suggest that intervention focusing on the AP-COP position in combination with ankle dorsiflexion or trunk flexion would be useful to coordinate the contribution of the knee extensor moment during double-leg squatting.

Spatial Instability during Precision Grip-Lift in Children with Poor Manual Dexterity.

Although children with developmental coordination disorder (DCD) show impaired precision grip control due to a sensory-motor integration deficit, their spatial instability (such as changes in force direction and object roll during a precision grip task) is unclear. Herein, we investigated the spatial instability in the precision grip force control of children with poor manual dexterity. We divided 66 school-aged children who performed a precision gripping and lifting of heavy- or lightweight objects into those with low manual dexterity (n = 11) and those with high manual dexterity (n = 55) as revealed by the Movement Assessment Battery for Children (2nd edition). The group and weight effects were then determined. The results revealed that the total trajectory lengths of the center of pressure (COP) were longer in the lightweight object data of the children in the low-manual-dexterity group and were related to the children’s grip force. The low-manual-dexterity group also showed a shifted COP position from the center of the object in the medial–lateral direction and in the object roll regardless of the object’s weight; these were closely related in both weights’ tests. These results demonstrated that children with poor manual dexterity show spatial instability and different adaptations to the weight of objects during a precision grip task. Further studies are needed to determine whether these findings would be replicated in children with a diagnosis of DCD.

Postural sway reduction by weak electrical noise into the wrist median nerve using portable stimulator

Stochastic resonance (SR) is a weak noise stimulation that improves the function of standing balance by increasing sensitivity to somatosensory information. SR implemented in the lower limbs may increase the standing balance function, but the effect of noise stimulation on upper limbs has not been investigated to date. This study aims to investigate the effect of weak electrical noise stimulation of the median nerve at the wrist on the balance control system function using a portable stimulator. Ten healthy individuals participated in the study. Each subject maintained quiet standing with their eyes closed for 40 s while receiving white noise electrical stimulation to the median nerve at the wrist. Center of pressure (COP) displacement and change in the joint position (left and right waist) were measured and compared between a no-stimulus trial (control trial) and a stimulus intensity trial that maximized the effect of SR (optimal trial). Experimental results show that weak electrical noise stimulation of the median nerve at the wrist stabilized the COP and joint position. The anteroposterior (AP) standard deviation of the optimal trial were significantly reduced compared to the control trial in terms of COP and left and right waist, and AP low-frequency range power of the optimal trial were significantly reduced compared to the control trial in terms of COP and left waist. AP mean velocity and AP high-frequency range power at the left waist were significantly reduced in the optimal trial. It was concluded that weak electrical noise stimulation applied to the median nerve can reduce static postural sway.

Balance control in unstable sitting in individuals with an acute episode of low back pain

BackgroundLow back pain (LBP) is associated with altered postural control, mostly observed at later stages in the LBP trajectory. It is unclear whether postural control differs in the acute phase of LBP. Research questionIs postural control different in the acute phase of LBP (<2 weeks) and do differences depend on pain intensity, psychological features and/or availability of vision to control posture? MethodsCross-sectional study design. An unstable sitting paradigm (to reduce the contribution of the legs) assessed postural control of participants with acute LBP (n = 133) and pain-free controls (n = 74). Centre of pressure (CoP) reflected seat movements. Participants balanced with eyes closed, open, or with visual feedback of the anteroposterior CoP position. Balance performance was expressed by CoP displacement and velocity, and stabilogram diffusion analysis. Generalised estimating equations (GEEs) including body mass index, sex, and safety bar touch, tested differences between groups and between balance conditions. Separate GEEs were used to model performance measures and bar touch (yes/no) including pain intensity, disability and psychological features. ResultsCoP displacement and critical point coordinates (time and distance where CoP diffusion rate or spread slows) were larger in LBP than pain-free controls independent of balance condition. Long-term diffusion rate was greater in LBP than controls with eyes closed. CoP velocity measures (RMS, short term diffusion rate) were not different between groups. Pain intensity and psychological features were not linearly related to balance performance in participants with acute LBP. Higher pain catastrophizing was associated with touching the safety bar. SignificancePostural control differs in acute LBP than pain-free controls. Findings might be explained by altered sensory processing, lesser ability to reweight proprioceptive information and/or less accurate trunk muscle control. Although not linearly related to pain-intensity or psychological features in the acute stage, reduced balance performance could potentially have impact on LBP recovery.

Mechanism and Effect of Tread Swing for Lower Limbs Strength Training Device

The aim of this study was to propose a tread swing mechanism for lower-limb strength training devices and to confirm its effects. In the standing position and for training the lower limbs, if the tread-surface angle is inappropriate, the posture of the knee joints gets affected, and knee adduction/valgus moments, which result in knee stress, get generated. The target training exercises are the front-back leg scissors and open-close leg triangle exercises. With regard to the swing of the tread, it is necessary to realize a pitch/yaw rotation and a roll/yaw rotation for the former and the latter exercises, respectively. As a result, knee joint stress can be reduced by moving the center of pressure (COP). The proposed mechanism has a further differential mechanism that utilizes the difference between the pulley diameters. The translational movement force of the tread is transmitted as the torque of the swing motion for the pitch, roll, and yaw through the effects of a differential mechanism. The rate of the swing angle can be changed by adjusting the pulley diameter. As a result of evaluating the effect of exercises using a manufactured device, it was confirmed that the tread performed a predetermined swing motion. It was also confirmed that the COP position changed. Therefore, it is expected that knee joint stress will reduce. Rehabilitation and strength training that result in small knee joint stresses and generate large muscle load are in great demand for people experiencing knee joint failure.

Center of pressure position in the touches of the star excursion balance test in healthy individuals

BackgroundThe Star Excursion Balance Test (SEBT) is a clinical test that aims to assess postural control. Its interpretation is related to the understanding of the motor specificities required. Adjustments must be made to the center of pressure (COP) to maintain balance during testing movements. Comprehend the specifics of these adjustments for each direction can allow the development of more suitable exercises for balance training. The aim was to compare the positions of the COP on the different directions of the SEBT and correlate the reachs obtained in the SEBT with the distances from the COP to the borders of the base of support (BOS). MethodsSixteen healthy subjects participated in the study. Measurements were made by performing the SEBT over the force platform. The Kruskal-Wallis test followed by Bonferroni's post hoc test was used to compare directions. The Pearson correlation test was used to check the correlation of parametric variables and Spearman correlation test for the nonparametric ones. ResultsThe position of the COP at the touch differs from the anterior direction to the other directions of the SEBT and the performance in this direction is correlated with the proximity of the COP to the anterior limit of the support base. The performances in the other directions did not correlate with the COP position. ConclusionThe requirements of the compensation mechanisms for postural control are different between the directions of the SEBT.

Multi-Cue Haptic Guidance Through Wearables for Enhancing Human Ergonomics.

Wearable haptic systems can be easily integrated with the human body and represent an effective solution for a natural and unobtrusive stimulus delivery. These characteristics can open interesting perspectives for different applications, such as haptic guidance for human ergonomics enhancement, e.g. during human-robot collaborative tasks in industrial scenarios, where the usage of the visual communication channel can be problematic. In this work, we propose a wearable multi-cue system that can be worn at the arm level on both the two upper limbs, which conveys both squeezing stimuli (provided by an armband haptic device) and vibration, to provide corrective feedback for posture balancing along the user's frontal and sagittal plane, respectively. We evaluated the effectiveness of our system in delivering directional information to control the user's center of pressure position on a balancing board. We compared the here proposed haptic guidance with visual guidance cues. Results show no statistically significant differences in terms of success rate and time for task completion for the two conditions. Furthermore, participants underwent through a Subjective Quantitative Evaluation and a NASA-TLX test, evaluating the wearable haptic system as intuitive and effective.

Static and dynamic stabilometric force platform study of spinopelvic anterior sagittal imbalance

Background dataAnterior sagittal imbalance (ASI) is a severity factor in spinal pathology. Stabilometric study of the dynamic position of the center of pressure (CoP) assesses orthostatic control. These analyses provide the energy expenditure used for this control. HypothesisStabilometric signs are associated with ASI indicate increased energy expenditure. Patients and MethodsHealthy male volunteers were subjected to reversible ASI induced by wearing a kyphotic thermoformed thoracolumbar corset. The deformation was assessed by C7 tilt on EOS whole-spine views. Static and dynamic posturographic force platform study was performed under conditions of anteroposterior and mediolateral instability. Mean CoP position (Xmean, Ymean) was studied on statokinesigram, with scatter assessed as confidence ellipse (CE). Path length according to CE surface (LAS) indicated energy expenditure. The stabilogram quantified displacement over time as lengths (Lx, Ly) and amplitudes (Ax, Ay). ResultsThe corset significantly increased C7 tilt (p<0.0001). This did not significantly change mean CoP positions (Xmean and Ymean), but LAS was significantly increased (p=0.003). Static tests showed changes in Ly (p=0.0008) and Ax (p=0.003), and dynamic tests showed changes in Ly (p<0.0001), Lx (p<0.0001), Ax (p<0.0001), Ay (p<0.05) and CE (p<0.004). DiscussionPosturographic parameters were impacted by inducing ASI in healthy subjects. Significant differences were seen in stabilography, CE and LAS, were greater on dynamic testing, and correlated with radiologic sagittal balance. Force platforms can reveal increased energy expenditure in maintaining posture. Level of evidenceII; Single-center prospective study involving healthy volunteers.

The Effects of Altering the Center of Pressure in Standing Subjects Exposed to Foot-Transmitted Vibration on an Optimized Lumped-Parameter Model of the Foot

Many workers are exposed to foot-transmitted vibration, which can lead to the development of vibration-induced white foot: a debilitating condition with neurological, vascular and osteoarticular symptoms. To design effective prevention mechanisms (i.e., boots and insoles) for isolating workers from vibration exposure, continued model development of the foot’s biodynamic response in different positions is necessary. This study uses a previously developed model of the foot–ankle system (FAS) to investigates how altering the center of pressure (COP) location can change the biodynamic response of the FAS to standing vibration exposure. Formerly published experimental responses for apparent mass and transmissibility at five anatomical locations in three COP positions were used to optimize the model. Differences occurred with the Kelvin–Voigt elements used to represent the soft tissues of the foot sole: at the heel, the distal head of the metatarsals and distal phalanges. The stiffness increased wherever the COP was concentrated (i.e., forward over the toes or backward over the heel). The variability of the model parameters was always greatest when the COP was concentrated in the heel. This suggests future FAS models need to more clearly address how the soft tissue of the plantar fat pad is modelled.

A Novel Viewpoint on the Anticipatory Postural Adjustments During Gait Initiation.

Anticipatory postural adjustments (APAs) are the coordinated muscular activities that precede the voluntary movements to counteract the associated postural perturbations. Many studies about gait initiation call APAs those activities that precede the heel-off of the leading foot, thus taking heel-off as the onset of voluntary movement. In particular, leg muscles drive the center of pressure (CoP) both laterally, to shift the body weight over the trailing foot and backward, to create a disequilibrium torque pushing forward the center of mass (CoM). However, since subjects want to propel their body rather than lift their foot, the onset of gait should be the CoM displacement, which starts with the backward CoP shift. If so, the leg muscles driving such a shift are the prime movers. Moreover, since the disequilibrium torque is mechanically equivalent to a forward force acting at the pelvis level, APAs should be required to link the body segments to the pelvis: distributing such concentrated force throughout the body would make all segments move homogeneously. In the aim of testing this hypothesis, we analyzed gait initiation in 15 right-footed healthy subjects, searching for activities in trunk muscles that precede the onset of the backward CoP shift. Subjects stood on a force plate for about 10 s and then started walking at their natural speed. A minimum of 10 trials were collected. A force plate measured the CoP position while wireless probes recorded the electromyographic activities. Recordings ascertained that at gait onset APAs develop in trunk muscles. On the right side, Rectus Abdominis and Obliquus Abdominis were activated in 11 and 13 subjects, respectively, starting on average 33 and 54 ms before the CoP shift; Erector Spinae (ES) at L2 and T3 levels was instead inhibited (9 and 7 subjects, 104 and 120 ms). On the contralateral side, the same muscles showed excitatory APAs (abdominals in 11 and 12 subjects, 27 and 82 ms; ES in 10 and 7 subjects, 75 and 32 ms). The results of this study provide a novel framework for distinguishing postural from voluntary actions, which may be relevant for the diagnosis and rehabilitation of gait disorders.

Influence of Augmented Visual Feedback on Balance Control in Unilateral Transfemoral Amputees.

Patients with a lower limb amputation rely more on visual feedback to maintain balance than able-bodied individuals. Altering this sensory modality in amputees thus results in a disrupted postural control. However, little is known about how lower limb amputees cope with augmented visual information during balance tasks. In this study, we investigated how unilateral transfemoral amputees incorporate visual feedback of their center of pressure (CoP) position during quiet standing. Ten transfemoral amputees and ten age-matched able-bodied participants were provided with real-time visual feedback of the position of their CoP while standing on a pressure platform. Their task was to keep their CoP within a small circle in the center of a computer screen placed at eye level, which could be achieved by minimizing their postural sway. The visual feedback was then delayed by 250 and 500 ms and was combined with a two- and five-fold amplification of the CoP displacements. Trials with eyes open without augmented visual feedback as well as with eyes closed were further performed. The overall performance was measured by computing the sway area. We further quantified the dynamics of the CoP adjustments using the entropic half-life (EnHL) to study possible physiological mechanisms behind postural control. Amputees showed an increased sway area compared to the control group. The EnHL values of the amputated leg were significantly higher than those of the intact leg and the dominant and non-dominant leg of controls. This indicates lower dynamics in the CoP adjustments of the amputated leg, which was compensated by increasing the dynamics of the CoP adjustments of the intact leg. Receiving real-time visual feedback of the CoP position did not significantly reduce the sway area neither in amputees nor in controls when comparing with the eyes open condition without visual feedback of the CoP position. Further, with increasing delay and amplification, both groups were able to compensate for small visual perturbations, yet their dynamics were significantly lower when additional information was not received in a physiologically relevant time frame. These findings may be used for future design of neurorehabilitation programs to restore sensory feedback in lower limb amputees.

Deformable foot orthoses redistribute power from the ankle to the distal foot during walking

Recently, carbon fiber plates, or orthoses, have been incorporated into footwear to improve running performance, presumably through improved energy storage and return. However, few studies have explored the energetic effects these orthoses have on the distal foot, have utilized such orthoses in walking, and none have sought to specifically harness metatarsophalangeal joint deformation to store and return energy to the ankle–foot complex. To address these gaps, we developed and tested a deformable carbon fiber foot orthosis aiming to harness foot energetics and quantify the resulting effects on ankle energetics during walking in healthy adults. Eight subjects walked under three conditions: barefoot (BF), with minimalist shoes (SH), and with bilateral, deformable foot orthoses in the minimalist shoes (ORTH). Ankle and distal foot energetics, foot-to-floor and ankle angle, stance time, step length, and max center of pressure (COP) position were calculated. When walking with the orthoses, subjects showed 263.6% increase in positive distal foot work along with a 31.9% decrease in ankle work and little to no change in the overall ankle–foot complex work. Step length, stance time, and max anterior COP position significantly increased with orthosis use. No statistical or visual differences were found between BF and SH conditions indicating that our findings were due to the foot orthoses. These results suggest this foot orthosis redistributes power from the ankle to the distal foot for healthy adults, reducing the energetic demand on the ankle. These results lay the foundation for designing orthotics and footwear to improve ankle–foot energetics for clinical populations.

Posture dependent ankle and foot muscle responses evoked by Achilles’ tendon vibration

To investigate the link between the triceps surae and the intrinsic muscles of the foot, often underestimated in posture maintenance, we asked how Achilles’ tendon vibration modulates the EMG activity of the soleus and flexor digitorum brevis (FDB) muscles during different postural tasks: sitting, standing and forward leaning. Young healthy participants (n = 19, age = 24 ± 7.4 years) stood for 60 s in three visually controlled postures, while vibration (1.5–1.8 mm, 80 Hz) was bilaterally applied over the Achilles' tendon during the middle 20 s. Center of Pressure (CoP) and EMG activity of the soleus and FDB muscle were summarized in 5 s epochs and compared across time (before, during and after vibration) and postural tasks. Achilles’ tendon vibration shifted the CoP position forward in sitting and backward in standing and leaning and increased the root mean square of the CoP velocity to a greater extent in standing and leaning compared to sitting. Soleus and FDB EMG amplitude also increased in response to vibration. These responses were posture dependent, being greater in standing (soleus: 57 %, FDB: 67 % relative to pre-vibration) compared to sitting (soleus: 36 %, FDB: 27 % relative to pre-vibration) and leaning (soleus: 26 %, FDB: 8% relative to pre-vibration). After vibration offset, both soleus and FDB showed sustained activation across all three postures. Results highlight the presence of Ia afferent projections from the soleus to the α motor neurons of the FDB muscle triggered by Achilles’ tendon vibration. This link is posture dependent serving a functional role in standing and forward leaning in the presence of externally applied perturbations.

Standing posture and balance modalities in unilateral transfemoral and transtibial amputees

IntroductionLower limb amputation impairs postural performance that could be characterized by biomechanical parameters. This study is to investigate postural performance of persons with transfemoral and transtibial amputation compared to controls without amputation. MethodsEight transtibial, nine transfemoral and twelve able-bodied males participated in this study. Lower limb joints, pelvis and trunk angles were obtained from an optoelectronic motion analysis system to evaluate body posture parameters. The mean, range and speed of the center of pressure (CoP) in both antero-posterior and medio-lateral axes as well as the ellipse area covered by 90% of CoP and free moment were calculated using a single force-plate. Results and discussionDifferences in body posture were only noted between the non-amputee and the transtibial groups. Transtibial amputees leaned more forwardly their trunk by 3.5° compared to able-bodied (p = 0.028). The mean CoP position in transfemoral amputees was closer to the non-amputated side than transtibial amputees (p = 0.034) and as compared to the dominant side in non-amputees (p = 0.042). Factor analysis revealed three postural performance modalities. Non-amputees postural performance was characterized solely by body posture parameters. Transfemoral amputees exclusively favored a modality associated with standing balance parameters, whereas transtibial amputees exhibited a mixed modality comprising a combination of postural and balance parameters. ConclusionThese findings support that the level of amputation is characterized by postural performance modalities different from non-amputees. Clinicians could apply this knowledge as part of their routine rehabilitation program to enhance postural and standing balance assessments in unilateral transfemoral and transtibial amputees.

The Effects of Static Stretching On Dynamic Postural Control During Maximum Forward Leaning Task

The purpose of this study was to determine how the application of static stretching to ankle plantar flexors affects postural control during maximum forward leaning. Twenty-six volunteer males (age 21.4 ± 1.2 years) were randomly assigned to stretching and control conditions. Participants conducted 5-min stretching on a stretch board for the stretching condition and were kept standing for 6-min for the control condition. Before and after intervention, the range of motion (ROM) at ankle dorsiflexion and the center of pressure (COP) excursion during maximal forward leaning were determined. Mean anteroposterior COP position, COP velocity and COP areas were calculated to compare the change in postural control. After stretching, ROM was significantly increased. During maximal forward leaning after stretching, both COP position and velocity showed significant increases compared to before stretching. Moreover, COP position and velocity in the stretching condition were significantly higher than in the control condition after stretching. No significant differences were found in COP area before and after stretching. Five-minute stretching increased not only ROM but also the anterior limit of stability while maintaining posture and led to faster COP shift than before stretching. These results indicate that static stretching would improve dynamic postural control as well.

Hematite Suspension based Absorbent Pad Inclined Slider Influenced by Slip and Squeeze Velocity with Altering Film Ratio

The effects of various entities like slip and squeeze velocities, inlet-outlet film ratio, and the material parameter have been fairly explored in a hematite suspension based absorbent (porous) pad inclined slider. Mathematical expressions for pressure, load capacity (lifting force), friction, friction coefficient, and position of centre of pressure (COP) in terms of the above physical parameters have been acquired. Jenkins model has been employed as a mathematical set of governing equations. It has been found that an increase in the squeeze velocity has enhanced the load capacity and diminished the friction coefficient whereas the escalating values of slip velocity and material properties have reversed the trends. Besides, the optimum value of the inlet-outlet film ratio for maximum load capacity has reduced with a rise in the squeeze velocity. Improvement in material parameters shifted the position of COP slightly towards the inlet while an enhancement in the squeeze velocity and film ratio shifted the same slightly towards the outlet. The results acquired in the present paper will be helpful in designing and modifying the various types of fluid dynamic slider bearings.