Stance Foot Research Articles

Demonstrating the utility of Instrumented Gait Analysis in the treatment of children with cerebral palsy.

Instrumented gait analysis (IGA) has been around for a long time but has never been shown to be useful for improving patient outcomes. In this study we demonstrate the potential utility of IGA by showing that machine learning models are better able to estimate treatment outcomes when they include both IGA and clinical (CLI) features compared to when they include CLI features alone. We carried out a retrospective analysis of data from ambulatory children diagnosed with cerebral palsy who were seen at least twice at our gait analysis center. Individuals underwent a variety of treatments (including no treatment) between sequential gait analyses. We fit Bayesian Additive Regression Tree (BART) models that estimated outcomes for mean stance foot progression to demonstrate the approach. We built two models: one using CLI features only, and one using CLI and IGA features. We then compared the models' performance in detail. We performed similar, but less detailed, analyses for a number of other outcomes. All results were based on independent test data from a 70%/30% training/testing split. The IGA model was more accurate than the CLI model for mean stance-phase foot progression outcomes (RMSEIGA = 11∘, RMSECLI = 13∘) and explained more than 1.5 × as much of the variance (R2IGA = .45, R2CLI = .28). The IGA model outperformed the CLI model for every level of treatment complexity, as measured by number of simultaneous surgeries. The IGA model also exhibited superior performance for estimating outcomes of mean stance-phase knee flexion, mean stance-phase ankle dorsiflexion, maximum swing-phase knee flexion, gait deviation index (GDI), and dimensionless speed. The results show that IGA has the potential to be useful in the treatment planning process for ambulatory children diagnosed with cerebral palsy. We propose that the results of machine learning outcome estimators-including estimates of uncertainty-become the primary IGA tool utilized in the clinical process, complementing the standard medical practice of conducting a through patient history and physical exam, eliciting patient goals, reviewing relevant imaging data, and so on.

A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice.

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Biomechanical Balance Measures During Timed Up and Go Test Improve Prediction of Prospective Falls in Older Adults

ObjectiveTo assess the feasibility of using biomechanical gait balance measures, the frontal and sagittal plane center of mass (COM)-Ankle angles, to prospectively predict recurrent falls in community-dwelling older adults. DesignA cohort study with a 1-year longitudinal follow-up. Logistic regression was used to test the ability of the COM-Ankle angles to predict prospective falls. SettingGeneral community. ParticipantsSixty older adults over the age of 70 years were recruited using a volunteer sample. InterventionsNot applicable. Main Outcome Measure(s)Biomechanical balance parameters: the sagittal and frontal plane COM-Ankle angles during the sit-to-walk and turning phases of the timed Up and Go test. The COM-Ankle angles are the inclination angles of the line formed by the COM and lateral ankle (malleolus) marker of the stance foot in the sagittal and frontal planes. We also included the following clinical balance tests in the analysis: Activity-Specific Balance Confidence, Berg Balance Scale, Fullerton Advanced Balance scale, and timed Up and Go test. Their abilities to predict falls served as a reference for the biomechanical balance parameters. ResultsWhen the biomechanical gait balance measures were added to all the confounders, the explained variance was increased from 25.3% to 50.2%. Older adults who have a smaller sagittal plane COM-Ankle angle at seat-off, a greater frontal plane COM range of motion during STW and a smaller frontal plane angle during turning were more likely to become recurrent fallers. Conclusion(s)Our results indicated that dynamic biomechanical balance parameters could provide valuable information about a participant's future fall risks beyond what can be explained by demographics, cognition, depression, strength, and past fall history. Among all biomechanical parameters investigated, frontal plane COM motion measures during STW and turning appear to be the most significant predictors for future falls.

An optimal signal selection method based on feature neighborhood using for human gait mode recognition

Signal selection is a crucial issue for classifiers. A feature neighborhood based method is proposed to select the optimal signals in this paper. The neighborhood of a feature is first defined to classify each example according to whether its feature value belongs to the neighborhood. A discernibility matrix is established based on all the classification results of the feature. The classification ability of a feature is then calculated according to its discernibility matrix. Furthermore, the classification ability of a signal combination is achieved by calculating the disjunction of the corresponding feature discernibility matrices. The optimal signal combination (O-combination) with the highest classification ability is finally selected. The proposed method is validated by using the data from two public databases of human motion. The results show that 2∼5 signals are selected from over 50 signals to be the O-combinations for human gait mode recognition. The accuracy rates of gait mode recognition (RARs) of these O-combinations are higher than those of other signal combinations with the same dimensionality. The RARs of the 4- and 5- dimensional O-combinations are even higher than that of the combination formed with all signals. Specifically, the RARs of the 4-dimensional O-combinations are 99.37% and 99.86% on the two public databases. In addition, it is found that the signal of clearance between swing foot and stance foot exists in most of the combinations with high RAR, which indicates that this signal cannot be ignored for gait mode recognition.

Digital Measures of Postural Sway Quantify Balance Deficits in Spinocerebellar Ataxia.

Maintaining balance is crucial for independence and quality of life. Loss of balance is a hallmark of spinocerebellar ataxia (SCA). The aim of this study was to identify which standing balance conditions and digital measures of body sway were most discriminative, reliable, and valid for quantifying balance in SCA. Fifty-three people with SCA (13 SCA1, 13 SCA2, 14 SCA3, and 13 SCA6) and Scale for Assessment and Rating of Ataxia (SARA) scores 9.28 ± 4.36 and 31 healthy controls were recruited. Subjects stood in six test conditions (natural stance, feet together and tandem, each with eyes open [EO] and eyes closed [EC]) with an inertial sensor on their lower back for 30 seconds (×2). We compared test completion rate, test-retest reliability, and areas under the receiver operating characteristic curve (AUC) for seven digital sway measures. Pearson's correlations related sway with the SARA and the Patient-Reported Outcome Measure of Ataxia (PROM ataxia). Most individuals with SCA (85%-100%) could stand for 30 seconds with natural stance EO or EC, and with feet together EO. The most discriminative digital sway measures (path length, range, area, and root mean square) from the two most reliable and discriminative conditions (natural stance EC and feet together EO) showed intraclass correlation coefficients from 0.70 to 0.91 and AUCs from 0.83 to 0.93. Correlations of sway with SARA were significant (maximum r = 0.65 and 0.73). Correlations with PROM ataxia were mild to moderate (maximum r = 0.56 and 0.34). Inertial sensor measures of extent of postural sway in conditions of natural stance EC and feet together stance EO were discriminative, reliable, and valid for monitoring SCA. © 2024 International Parkinson and Movement Disorder Society.

A four-week minimalist shoe walking intervention influences foot posture and balance in young adults-a randomized controlled trial.

Minimalist shoes (MS) are beneficial for foot health. The foot is a part of the posterior chain. It is suggested that interventions on the plantar foot sole also affect the upper segments of the body. This study aimed to investigate the local and remote effects along the posterior chain of four weeks of MS walking in recreationally active young adults. 28 healthy participants (15 female, 13 male; 25.3 ± 5.3 years; 70.2 ± 11.9 kg; 175.0 ± 7.8 cm) were randomly assigned to a control- or intervention group. The intervention group undertook a four-week incremental MS walking program, which included 3,000 steps/day in the first week, increasing to 5,000 steps/day for the remaining three weeks. The control group walked in their preferred shoe (no MS). We assessed the following parameters in a laboratory at baseline [M1], after the four-week intervention [M2], and after a four-week wash-out period [M3]: Foot parameters (i.e., Foot Posture Index-6, Arch Rigidity Index), static single-leg stance balance, foot-, ankle-, and posterior chain range of motion, and muscle strength of the posterior chain. We fitted multiple hierarchically built mixed models to the data. In the MS group, the Foot Posture Index (b = -3.72, t(51) = -6.05, p < .001, [-4.94, 2.51]) and balance (b = -17.96, t(49) = -2.56, p = .01, [-31.54, 4.37]) significantly improved from M1 to M2, but not all other parameters (all p >.05). The improvements remained at M3 (Foot Posture Index: b = -1.71, t(51) = -2.73, p = .009, [-4,94,0.48]; balance: b = -15.97, t(49) = -2.25, p = .03, [-29.72, 2.21]). Walking in MS for four weeks might be advantageous for foot health of recreationally active young adults but no chronic remote effects should be expected.

The deterministic condition for the ground reaction force acting point on the combined knee valgus and tibial internal rotation moments in early phase of cutting maneuvers in female athletes

BackgroundCombined knee valgus and tibial internal rotation (VL + IR) moments have been shown to stress the anterior cruciate ligament (ACL) in several in vitro cadaveric studies. To utilize this knowledge for non-contact ACL injury prevention in sports, it is necessary to elucidate how the ground reaction force (GRF) acting point (center of pressure (CoP)) in the stance foot produces combined knee VL + IR moments in risky maneuvers, such as cuttings. However, the effects of the GRF acting point on the development of the combined knee VL + IR moment in cutting are still unknown. MethodsWe first established the deterministic mechanical condition that the CoP position relative to the tibial rotational axis differentiates the GRF vector's directional probability for developing the combined knee VL + IR moment, and theoretically predicted that when the CoP is posterior to the tibial rotational axis, the GRF vector is more likely to produce the combined knee VL + IR moment than when the CoP is anterior to the tibial rotational axis. Then, we tested a stochastic aspect of our theory in a lab-controlled in vivo experiment. Fourteen females performed 60° cutting under forefoot/rearfoot strike conditions (10 trials each). The positions of lower limb markers and GRF data were measured, and the knee moment due to GRF vector was calculated. The trials were divided into anterior- and posterior-CoP groups depending on the CoP position relative to the tibial rotational axis at each 10 ms interval from 0 to 100 ms after foot strike, and the occurrence rate of the combined knee VL + IR moment was compared between trial groups. ResultsThe posterior-CoP group showed significantly higher occurrence rates of the combined knee VL + IR moment (maximum of 82.8%) at every time point than those of the anterior-CoP trials, as theoretically predicted by the deterministic mechanical condition. ConclusionThe rearfoot strikes inducing the posterior CoP should be avoided to reduce the risk of non-contact ACL injury associated with the combined knee VL + IR stress.

Can we enable individuals to reach further down without rounding their backs before beginning a lift? Examining the influence of starting foot and trunk position on reach depth

There is disagreement regarding the efficacy of ‘safe’ lifting recommendations for reducing low back disorder risk. These recommendations commonly focus on minimising lumbar spine flexion, which limits the range of allowable starting lift positions for that person. This study evaluated whether starting postural adaptations could allow a person to reach down further without rounding their lumbar spine before beginning a lift. Reach displacement was measured as participants performed a series of maximal reach tasks under different combinations of stance width, foot orientation and trunk inclination, with their lumbar spine motion restricted. There were no interactions between any of the three postural adaptations or any effect of stance width or trunk inclination. Seventy-nine percent of participants achieved their greatest reach displacement with their feet externally rotated, which contributed to a 4 cm greater reach displacement compared to a neutral foot orientation (p < 0.001). Practitioner summary: This study examined whether aspects of initial posture could influence the ability to adhere to ‘safe’ lifting recommendations across a range of lift heights. As a component of lifting (re)training interventions, practitioners should consider starting lift posture adaptations (e.g. manipulating foot external rotation) to improve capacity to adhere to recommendations.

Speech, Gait, and Vestibular Function in Cerebellar Ataxia with Neuropathy and Vestibular Areflexia Syndrome.

(1) Background: Cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS) is characterized by late-onset cerebellar ataxia, bilateral vestibulopathy, and sensory neuronopathy mostly due to biallelic RFC1 expansion. (2) Objectives: The aim of this case series is to describe vestibular, gait, and speech alterations in CANVAS via a systematic approach. (3) Methods: All patients (n = 5) underwent a standardized clinical-instrumental examination, including the perceptual and acoustic analysis of speech, instrumental gait, and balance analysis (posturographic data were acquired using a force plate [Kistler, Winterthur, Switzerland] while 3D gait analysis, inclusive of surface electromyography, was acquired using a motion capture system [SMART DX, BTS Bioengineering, Milan, Italy], a wireless electromyograph [FreeEMG, BTS Bioengineering, Milan, Italy]), and vestibular assessment with video-oculography. (4) Results: Five patients were included in the analysis: three females (patients A, B, C) and two males (patients D and E) with a mean age at evaluation of 62 years (SD ± 15.16, range 36-74). The mean age of symptoms' onset was 55.6 years (SD ± 15.04, range 30-68), and patients were clinically and instrumentally evaluated with a mean disease duration of 6.4 years (SD ± 0.54, range 6-7). Video-Frenzel examination documented spontaneous downbeat nystagmus enhanced on bilateral gaze in all patients, except for one presenting with slight downbeat nystagmus in the supine position. All patients exhibited different degrees of symmetrically reduced VOR gain for allsix semicircular canals on the video-head impulse test and an unexpectedly normal ("false negative") VOR suppression, consistent with combined cerebellar dysfunction and bilateral vestibular loss. Posturographic indices were outside their age-matched normative ranges in all patients, while 3D gait analysis highlighted a reduction in ankle dorsiflexion (limited forward rotation of the tibia over the stance foot during the stance phase of gait and fatigue of the dorsiflexor muscles) and variable out-of-phase activity of plantar flexors during the swing phase. Finally, perceptual-acoustic evaluation of speech showed ataxic dysarthria in three patients. Dysdiadochokinesis, rhythm instability, and irregularity were observed in the oral diadochokinesis task. (5) Conclusions: CANVAS is a recently discovered syndrome that is gaining more and more relevance within late-onset ataxias. In this paper, we aimed to contribute to a detailed description of its phenotype.

Overground Robotic Gait Trainer mTPAD Improves Gait Symmetry and Weight Bearing in Stroke Survivors

Stroke is a leading cause of disability, impairing the ability to generate propulsive forces and causing significant lateral gait asymmetry. We aim to improve stroke survivors’ gaits by promoting weight-bearing during affected limb stance. External forces can encourage this; e.g., vertical forces can augment the gravitational force requiring higher ground reaction forces, or lateral forces can shift the center of mass over the stance foot, altering the lateral placement of the center of pressure. With our novel design of a mobile Tethered Pelvic Assist Device (mTPAD) paired with the DeepSole system to predict the user’s gait cycle percentage, we demonstrate how to apply three-dimensional forces on the pelvis without lower limb constraints. This work is the first result in the literature that shows that with an applied lateral force during affected limb stance, the center of pressure trajectory’s lateral symmetry is significantly closer to a 0% symmetry (5.5%) than without external force applied (−9.8%,p&lt;0.05). Furthermore, the affected limb’s maximum relative pressure (p) significantly increases from 233.7p to 234.1p (p&lt;0.05) with an applied downward force, increasing affected limb loading. This work highlights how the mTPAD increases weight-bearing and propulsive forces during gait, which is a crucial goal for stroke survivors.

Effectiveness of Center of Pressure Trajectory as Anticipatory Postural Adjustment Measurement in Parkinson’s Disease With Freezing of Gait History

Background Evidence showed that patients with Parkinson’s disease (PD) who have a history of freezing of gait (FOG) have hypometric anticipatory postural adjustment (APA) during gait initiation (GI) compared to PD without FOG. Objectives This study aimed to test the feasibility of center of pressure (COP) displacement during GI as the measure of APA in PD with and without a history of FOG. Methods Patients with PD underwent COP trajectory measurements, including duration, length, velocity, and acceleration in different phases of APA (APA1, APA2a, APA2, and LOC), as well as evaluation of New Freezing of Gait Questionnaire (NFOG-Q), Tinetti balance and gait score, and Postural Instability and Gait Difficulty (PIGD) score in the on and off medication states. Results The duration (seconds) of APA2a, APA2b, and LOC were highest while velocity in mediolateral direction (X) (m/s), including APA1, APA2a, APA2b, and LOC showed lowest in PD with FOG. Velocity in the mediolateral direction in different phases of APA increased in patients with FOG after dopaminergic therapy. APA2a (seconds) and APA2b (X) (m/s) were significantly associated with NFOG-Q part II, APA2b (X) (m/s) was significantly associated with NFOG-Q part III, and APA2a (seconds) was significantly associated with Tinetti balance and gait and PIGD score. Conclusions PD with FOG history showed a favorable response of APAs to dopaminergic replacement. The APA parameters by COP trajectory, especially lateral COP shift toward the stance foot (APA2b (X) (m/s) and APA2a (seconds)) are surrogate markers to assess PD with FOG history.

Relation of Flatfoot Severity with Flexibility and Isometric Strength of the Foot and Trunk Extensors in Children.

Flatfoot is a deformity in which the foot is flattened due to a decrease in or loss of the medial longitudinal arch. Few studies have investigated the relationship between the severity of flat feet, trunk strength, and joint flexibility. The aim of this study is to investigate the relationship between the severity of flatfoot and joint flexibility and foot and trunk strength in children with flexible flatfoot. This study included 16 children (boys, 12; girls, 4; age, 4~8 years) with flexible flatfeet. We examined the resting calcaneal stance position angle (RCSPA) and foot posture index (FPI) scores for clinical severity and radiographic parameters, such as calcaneal pitch angle, talometatarsal angle (TMA), and talocalcaneal angle (TCA). Muscle thicknesses of the tibialis posterior (TP), peroneus longus (PL), and L1 multifidus were measured by sonography. Isometric contraction of ankle inversion, eversion in a seating position, and lumbar extension at a prone position were induced using a handheld dynamometer to measure the maximum muscle strength for each muscle. Beighton's scoring system was used to assess joint flexibility by evaluating the hyperextension of the joint for each category when performing stretching motion. Spearman's rank correlation coefficient for nonparametric data was used. The FPI showed a moderately negative correlation with the muscle thickness of TP (r = -0.558, p = 0.009) and L1 multifidus (r = -0.527, p = 0.012), and the strength of the ankle inverter (r = -0.580 p = 0.005) and lumbar extensor (r = -0.436 p = 0.043). RCSPA showed a moderately positive correlation with TCA (r = 0.510, p = 0.006). Beighton's score showed no significant correlation with all parameters. In children with flatfoot, FPI reflected the clinical severity; thus, the more severe the symptoms, the weaker the ankle inverter and lumbar extensor.

Relationships between kinematic characteristics and ratio of forces during initial sprint acceleration

ABSTRACT In track sprinting, acceleration performance is largely determined by the ability to generate a high ratio of forces (RF), but the technical features associated with this remain unknown. This study therefore investigated the relationships between selected kinematic characteristics and RF during the initial acceleration phase. Fourteen male sprinters completed two maximal 60 m sprints from a block start. Full-body kinematic and external kinetic data were obtained from the first four steps, and the relationships between selected kinematic characteristics and mean RF over the first four steps were determined. Placing the stance foot further behind (or less far in front of) the whole-body centre of mass at touchdown was significantly related to greater RF (r = −0.672), and more anterior orientation of the proximal end of the foot (r = −0.724) and shank (r = −0.764) segments at touchdown were also significantly related to greater RF. Following touchdown, greater ankle dorsiflexion range of motion during early stance was significantly related to greater RF (r = 0.728). When aiming to enhance RF during initial acceleration, practitioners should be encouraged to focus on lower leg configurations when manipulating touchdown distance, and the role of dorsiflexion during early stance is also an important consideration.

Interaction between Feet and Gaze in Postural Control.

In the last decade, the number of postural studies in humans, in particular on deficits in postural control in patients, has increased. In the present article, we review studies on postural control with a particular focus on the role of foot and visual inputs in a quiet postural stance. A search and synthesis of articles identified through the electronic databases Scopus, Web of Science, EBSCO, PubMed, and ResearchGate published until 2021 was performed. The aim of this review is to provide reference values for further studies dealing with postural control in both healthy and pathologic subjects and to encourage the development of suitable protocols that take into account the specificity of the different systems responsible for controlling human balance.

Kinematic adaptations to restricting spine motion during symmetrical lifting

When lifting an object from the ground a person has many possible whole-body movement solutions to accomplish the task. It is unclear why lifters use most of their available lumbar spine flexion range-of-motion despite many ergonomic guidelines advising against doing so. Experimentally restricting spine motion and observing compensatory movement strategies is one approach to address this knowledge gap. A kinematic analysis was performed on 16 participants who completed symmetrical lifting tasks with and without wearing a spine motion-restricting device. Sagittal trunk, lumbar spine, and lower extremity kinematics, along with stance width and foot orientation in the transverse plane were evaluated between restricted and unrestricted lifting conditions. Restricting spine motion required greater ankle dorsiflexion (p < 0.001), knee flexion (p < 0.001), and hip flexion (p < 0.001) motion in comparison to unrestricted lifting. Motion was reallocated such that hip flexion showed the largest increase in restricted lifting, followed by ankle dorsiflexion, then knee flexion compared to unrestricted lifting. Trunk inclination decreased (i.e., more upright) in restricted compared to unrestricted lifting (p < 0.001). Neither stance width (p = 0.163) nor foot orientation (p = 0.228) were affected by restricting spine motion. These adaptive movements observed indicate lower extremity joint motion must be available and controlled to minimize lumbar spine flexion during lifting.

Trunk and lower-extremity kinematics differ based on step-down tap variation: An assessment of methodology for a return-to-play protocol using motion analysis

BackgroundThe step-down tap (SDT) is a commonly used task to assess unilateral neuromuscular control and to identify deficient movement patterns of the trunk and lower extremities. However, instruction of the SDT varies greatly in recent reports, which may alter the clinical interpretation of potential movement deficiencies. Research questionThe purpose of this study was to identify differences in trunk and lower extremity kinematics between variations of a step-down tap that differ based on step direction, fixing the arms or stance foot, and trial collection methods. MethodsThis study followed a single-group repeated measures design in a laboratory setting. Three-dimensional angles of the trunk, hip, and knee of 18 participants were evaluated at 60 degrees of knee flexion and at maximum squat depth during six SDT variations. Wilcoxon signed rank tests were performed to determine the effects of an anterior verse lateral step direction, a fixed arm or stance foot position, and an individual verse continuous trial collection method. ResultsKnee flexion, external pelvic rotation, and external trunk rotation were greater in the anterior SDT, while the lateral SDT elicited greater pelvic tilt and hip flexion. Additionally, overall squat depth was greater across participants during the anterior SDT. Few clinically significant differences (≥3°) were observed due to fixing arm or stance foot position, and no differences were identified based on trial collection methods. SignificanceThe standardization of task instructions for motion analysis protocols utilized for research purposes and/or clinical decision-making is crucial. Specifically, for the SDT, the authors recommend using the anterior step direction. A fixed arm and stance foot position is not necessary, and trials may be collected individually or continuously based on convenience for a small number of repetitions.

Differences in mediolateral dynamic stability during gait initiation according to whether the non-paretic or paretic leg is used as the leading limb.

We investigated mediolateral dynamic stability at first foot off and first initial contact during gait initiation according to whether the paretic or non-paretic leg was used as the leading limb. Thirty-eight individuals with stroke initiated gait with the paretic and non-paretic legs as the leading limb, and their movements were measured using a 3D motion analysis system. Margin of stability (i.e., the length between the extrapolated center of mass and lateral border of the stance foot) was used as an index of dynamic stability, with a large value indicating dynamic stability in the lateral direction. However, an excessively large margin of stability value (i.e., when the extrapolated center of mass is outside the medial border of the stance foot) indicates dynamic instability in the medial direction. Differences in the margin of stability between tasks were compared using the Wilcoxon signed-rank test. The minimum margin of stability was observed just before first foot off. When the non-paretic leg was used as the leading limb, the margin of stability tended to be excessively large at first foot off compared with when the paretic leg was used (p < 0.001). In other words, the extrapolated center of mass was outside the medial border of the paretic stance foot. In conclusion, lateral stability was achieved when using the non-paretic leading limb because the extrapolated center of mass was located outside the medial border of the stance foot. However, medial dynamic stability was lower for the non-paretic leading limb compared with the paretic leading limb.

The effect of constraining mediolateral ankle moments and foot placement on the use of the counter-rotation mechanism during walking

During walking, the center of mass (CoM) position can be controlled relative to the base of support by shifts of the center of pressure through modulation of foot placement and ankle moments (CoP-mechanism). An additional mechanism is the counter-rotation mechanism, i.e. changing the angular momentum of segments around the CoM to change the direction of the ground reaction force. It is unknown if, and how, humans use the counter-rotation mechanism to accelerate the CoM during walking and how this interacts with the CoP-mechanism. Thirteen healthy adults walked on a treadmill, while full-body kinematic and force plate data were obtained. The contributions of the CoP and the counter-rotation mechanisms to CoM-acceleration during steady-state walking, walking on LesSchuh (i.e. constraining mediolateral CoP shifts underneath the stance foot) and walking on LesSchuh at 50% of normal step width, constraining both foot placement and ankle mechanisms (LesSchuh50%) were calculated. The within-stride variance in CoM-acceleration due to the CoP-mechanism was smaller and the within-stride variance in CoM-acceleration due to the counter-rotation mechanism was larger during LesSchuh50% compared to steady-state walking. This suggests that the counter-rotation mechanism is used to stabilize gait when needed, but the CoP-mechanism was the main contributor to the total CoM-acceleration. The use of the counter-rotation mechanism may be limited, because angular accelerations ultimately need to be reversed and because of interference with other task constraints, such as head stabilization and preventing interference with the gait pattern.

Balance Recoverability and Control of Bipedal Walkers With Foot Slip.

Low-friction foot/ground contacts present a particular challenge for stable bipedal walkers. The slippage of the stance foot introduces complexity in robot dynamics and the general locomotion stability results cannot be applied directly. We relax the commonly used assumption of nonslip contact between the walker foot and the ground and examine bipedal dynamics under foot slip. Using a two-mass linear inverted pendulum model, we introduce the concept of balance recoverability and use it to quantify the balanced or fall-prone walking gaits. Balance recoverability also serves as the basis for the design of the balance recovery controller. We design the within- or multi-step recovery controller to assist the walker to avoid fall. The controller performance is validated through simulation results and robustness is demonstrated in the presence of measurement noises as well as variations of foot/ground friction conditions. In addition, the proposed methods and models are used to analyze the data from human walking experiments. The multiple subject experiments validate and illustrate the balance recoverability concept and analyses.

Influence of feet’s position on maximum forward lean using a new estimate of functional balance

Purpose Functional stability is crucial to the daily activity of an independent person, functional balance testing is widely used in laboratories and has proven to be a reliable indicator of fall risk. So far, only few studies have paid attention to the impact of foot positioning on the results of functional balance measurements. Methods Thirty healthy adults took part in experiment. LOS test was performed for four stance position: preferred width, wide stance (feet parallel, 28 cm apart), narrow stance (feet together) and angle stance (heels together, toes pointing outside, 90O angle between them) with eyes opened and closed. Results The results of the study show significant differences between angle and narrow stance according to wide and preferred width stances – angle and narrow positions didn’t allow participants to lean as far as other positions. Vision had stabilizing influence on maximum forward lean in all tested positions. Conclusions Feet position influence maximum forward lean. The width of the stance is not critical for the functional balance. Lack of visual control deteriorates functional balance. Researchers should use parallel feet placement in research.