Dynamic stability during walking in children with and without cerebral palsy

BackgroundCerebral palsy (CP) is associated with a high risk of falling during walking. Many gait abnormalities associated with CP likely alter foot placement and center of mass (CoM) movement in a way that affects anterior or lateral dynamic stability, in turn influencing fall risk.Research questionDo children with CP demonstrate altered anterior or lateral dynamic stability compared to typically-developing (TD) children?MethodsIn this case-control, observational study, we measured gait kinematics of two groups of children (15 CP, 11 GMFCS level I, 4 GMFCS level II; 14 TD; age 5–12) in walking conditions of a preferred speed, a fast speed, and a preferred speed while completing a cognitive task. For dominant and non-dominant limbs, the margin of stability (MoS), a spatial measure of dynamic stability, was calculated as the distance between the edge of the base of support and the CoM position after accounting for scaled velocity. Statistical comparisons of were made using mixed factorial ANOVAs. Post hoc comparisons were Sidak adjusted.ResultsThe anterior MoS before foot strike and at mid-swing differed between each condition but not between groups. Based on the minimum lateral MoS, children with CP had more stability when bearing weight on their non-dominant limb compared to TD children. These differences were not apparent when on the dominant limb.SignificanceThis high-functioning group of children with CP exhibited a more conservative lateral stability strategy during walking when bearing weight with the non-dominant limb. This strategy may be protective against lateral falls. We observed no between-group differences in anterior stability. Because CP has been previously associated with impaired anterior balance reactions, and there was no observed compensation in anterior gait stability, this lack of group differences could contribute to a higher risk of falling in that direction.     

The effect of obesity on whole-body angular momentum during steady-state walking

BackgroundIndividuals with obesity demonstrate deficits in postural stability, leading to increased fall risks. Controlling whole-body angular momentum is essential for maintaining postural stability during walking and preventing falls. However, it is unknown how obesity impacts whole-body angular momentum during walking.Research purposeTo investigate the change in angular momentum about the body’s COM during walking in individuals with different degrees of obesity.MethodsThirty-eight young adults with different body mass index (BMI) scores walked barefoot at their preferred speed on a treadmill for 2 min. The whole-body angular momentum has been quantified from ground reaction force and moment data to capture the rotational behavior of walking in individuals with obesity without relying solely on placing markers on anatomical landmarks.ResultsWe found that adults with higher BMI scores walked slower with shorter step length, wider step width, and longer double support time (ps<.01). Ranges of the frontal- and transverse-plane angular momentum were greater in adults with higher BMI scores (ps<.01), while no difference was observed between BMI groups in the total sum of changes in whole-body angular momentum in any plane (ps>.05).SignificanceObesity not only decreased walking speed but also limited the ability to control mediolateral stability during walking. Investigating how obesity affects whole-body angular momentum may help better understand why adults with obesity have atypical gait with poor balance, address fall risk factors, and facilitate participation in physical activities.     

Dynamic structure of variability in joint angles and center of mass position during user-driven treadmill walking

BackgroundOverground locomotion exhibits greater movement variability and less dynamic stability compared to typical fixed-speed treadmill walking. To minimize the differences between treadmill and overground locomotion, researchers are developing user-driven treadmill systems that adjust the speed of the treadmill belts in real-time based on how fast the subject is trying to walk.Research questionDoes dynamic structure of variability, quantified by the Lyapunov exponent (LyE), of joint angles and center of mass (COM) position differ between a fixed-speed treadmill (FTM) and user-driven treadmill (UTM) for healthy subjects?MethodsEleven healthy, adult subjects walked on a user-driven treadmill that updated its speed in real-time based on the subjects’ propulsive forces, location, step length, and step time, and at a matched speed on a typical, fixed-speed treadmill for 1-minute. The LyE for flexion/extension joint angles and center of mass position were calculated.ResultsSubjects exhibited higher LyE values of joint angles on the UTM compared to the FTM indicating that walking on the UTM may be more similar to overground locomotion. No change in COM LyE was observed between treadmill conditions indicating that subjects’ balance was not significantly altered by this new training paradigm.SignificanceThe user-driven treadmill may be a more valuable rehabilitation tool for improving gait than fixed-speed treadmill training, as it may increase the effectiveness of transitioning learned behaviors to overground compared to fixed-speed treadmills.     

Knee loading patterns of the non-paretic and paretic legs during post-stroke gait

BackgroundPost-stoke gait disorders could cause secondary musculoskeletal complications associated with excessive repetitive loading. The study objectives were to 1) determine the feasibility of measuring common proxies for dynamic medial knee joint loading during gait post-stroke with external knee adduction (KAM) and flexion moments (KFM) and 2) characterize knee loading and typical load-reducing compensations post-stroke.MethodsParticipants with stroke (n = 9) and healthy individuals (n = 17) underwent 3D gait analysis. The stroke and healthy groups were compared with unpaired t-tests on peak KAM and peak KFM and on typical medial knee joint load-reducing compensations; toe out and trunk lean. The relationship between KAM and load-reducing compensations in the stroke group were investigated with Spearman correlations.ResultsMean (SD) values for KAM and KFM in the healthy group[KAM = 2.20 (0.88)%BW*ht; KFM = 0.64 (0.60)%BW*ht] were not significantly different from the values for the paretic [KAM = 2.64 (0.98)%BW*ht; KFM = 1.26 (1.13)%BW*ht] or non-paretic leg of the stroke group[KAM = 2.23(0.62)%BW*ht; KFM = 1.10 (1.20)%BW*ht]. Post hoc one sample t-tests revealed greater loading in stroke participants on the paretic (n = 3), non-paretic (n = 1) and both legs (n = 2) compared to the healthy group. The angle of trunk lean and the angle of toe out were not related to KAM in the stroke group.DiscussionMeasurement of limb loading during a gait post-stroke is feasible and revealed excessive loading in individuals with mild to moderate stroke compared to healthy adults. Further investigation of potential joint degeneration and pain due to repetitive excessive loading associated with post-stroke gait is warranted.     

Effects of augmented somatosensory input using vibratory insoles to improve walking in individuals with chronic post-stroke hemiparesis

BackgroundStroke survivors suffer from hemiparesis and somatosensory impairments, which adversely impact walking performance, placing them at higher risks for trips and falls. Post-stroke, somatosensory deficits are commonly observed as impaired interpretation of afferent input and increased threshold. Diminishing or augmenting somatosensory inputs via various techniques have been demonstrated to be able to modify static and dynamic balance, postural and locomotor control in non-neurologically impaired as well as neurologically impaired individuals.Research question: We sought to investigate whether enhancing somatosensory input using vibratory insoles, can improve post-stroke gait. We hypothesized that with augmentation of somatosensory input at the soles via vibratory insoles would improve post-stroke gait via increased propulsive forces, decreased braking forces and increased ankle angle movements in the paretic legs of individuals with chronic post-stroke hemiparesis.MethodsFifteen individuals with chronic post-stroke hemiparesis and 15 age-similar non-neurologically impaired controls participated in this cross-sectional study. Enhanced somatosensory stimulation was delivered using a pair of tactor-embedded insoles, providing suprathreshold vibratory stimulation to the bottom of the feet. Participants walked over an instrumented treadmill with self-selected speeds, under 5 conditions: no insole in shoe (NT), insoles in shoe with no vibration (BOFF), vibration under both feet (BON), vibration under one foot only (ION, CON). Kinetics and kinematics during walking were recorded and analyzed offline.ResultsSuprathreshold vibratory stimulations did not alter gait kinetics under any stimulation conditions. We observed increased paretic ankle dorsiflexions in the paretic legs, when vibratory stimuli were applied unilaterally.SignificanceVibratory stimulations applied at suprathreshold intensity to the bottom of the feet to augment somatosensory feedback can potentially be used as a low-cost solution to address the inadequate toe clearance during walking in people post-stroke, which is an important goal in post-stroke rehabilitation.     

External feedback during walking improves measures of plantar pressure in individuals with chronic ankle instability

BackgroundIndividuals with chronic ankle instability (CAI) commonly present with an altered walking gait which favors the lateral aspect of their foot. Current rehabilitative protocols are unable to address these gait modifications which are potentially hindering improvements in patient-reported outcomes. Protocols for gait retraining are scarce, thus there is a need to develop intervention strategies and instruments to specifically target foot motion to address gait deficits in individuals with CAI.Research QuestionTo determine the ability of a novel laser device providing external visual feedback (ExFB) during real-time to cause alterations in plantar pressure measures in individuals with CAI.MethodsTwenty-six participants with CAI walked on a treadmill while real-time plantar pressure measures were being recorded during a baseline and feedback condition. Baseline trials were compared with ExFB trials within each subject.ResultsThe ExFB condition was able to significantly reduce plantar pressures on the lateral midfoot and forefoot compared to baseline. A statistically significant medial shift in center of pressure trajectory was also observed in the ExFB condition compared to baseline.SignificanceReal-time external feedback provided by a novel laser device has the ability to reduce lateral column plantar pressures during walking in individuals with CAI.     

Tibial and calcaneal coupling during walking in those with chronic ankle instability

BackgroundIt is estimated that nearly 2 million individuals sprain their ankle each year in the US. A majority of these are recurrent injuries, which often results in chronic ankle instability. To better understand the cause of instability, previous research has looked at the coupling or coordination between leg and foot motion during locomotion.Research QuestionDetermine the coupling between the tibia and the calcaneus during the stance phase of walking in those without a history of ankle instability compared to those with either moderate or severe instability.MethodsFifty-four individuals between the age of 18-30 years (15 males; 39 females) participated in this study. Each participant’s history of ankle sprains and score on the Cumberland Ankle Instability survey was used to assign them to either a no, moderate or severe instability group. Electromagnetic sensors attached to the tibia and calcaneus recorded three-dimensional movement of their tibia and calcaneus during the stance phase of barefoot over ground walking. The kinematic data was referenced to the subject’s standing position and time normalized to each subject’s stance phase duration. The relative phase (RP) angle and RP variability between tibia internal/external rotation and calcaneal inversion/eversion motion was then calculated. A one-way analysis of variance test was used to determine if significant differences existed between the three groups of subjects on mean RP angle or variability. An alpha level of .05 was used to determine statistical significance.ResultsA significant increase in RP angle and variability was found during the mid-stance phase of walking for those with severe ankle joint instability compared to those with moderate or no instability. Significance. The observed decreased coordination and increased coupling variability observed for those with severe ankle instability suggests either residual ligamentous damage, inadequate sensorimotor control, or both.     

O 089 - A soft robotic exosuit assisting the paretic ankle in patients post-stroke: Effect on muscle activation during overground walking

This study compared overground walking with and without exosuit assistance in post-stroke patients. Exosuit-assisted walking was found to improve paretic propulsion and ground clearance during swing, two common gait deviations in stroke patients. No changes in leg muscle activity was found, motivating further study of the exosuit as a tool for gait training during stroke rehabilitation.     

Motor adaptation to cognitive challenges and walking perturbations in healthy young adults

BackgroundCognitive-walking interference is manifested when simultaneously performing a cognitive task while walking. However, majority of the dual-task walking paradigms incorporated relatively short testing trials and were focused on posing a cognitive challenge by adding a secondary cognitive task but not introducing walking perturbations.Research questionHow do healthy young adults adapt to concurrent cognitive challenges and walking perturbations in terms of task prioritization and adaptation strategies to control walking stability?MethodsEighteen healthy young participants walked with and without (1) continuous treadmill platform sways (Perturbed and Unperturbed walking), and (2) performing one of the cognitive tasks: visual and auditory Stroop tasks, Clock task, Paced Auditory Serial Addition Test (PASAT), and walk only. Primary outcome measures included cognitive task performance, mediolateral dynamic margins of stability (MOS_ML), M-L local dynamic stability, stride time variability and the dual-task interference (DTI) on these measures.ResultsGait adjustments made during Perturbed walking did not improve walking stability but instead, showing more local instability and greater gait variability (all p < 0.001) than Unperturbed walking. Participants increased average MOS_ML during Clock and PASAT compared to Walk Only for both Perturbed and Unperturbed walking (THSD, p < 0.05). Participants had significantly less DTI on stride time variability during Unperturbed walking than during Perturbed walking (p < 0.001). Participants also had significantly greater DTI on PASAT performance during Perturbed than during Unperturbed walking (THSD, p < 0.05)SignificanceParticipants prioritized the walking task under a more challenging walking condition although the adjustments made during Perturbed walking were not sufficient to maintain a similar level of walking stability as Unperturbed walking. Adjustments to the cognitive-walking challenges were differed by the type of cognitive tasks. The current findings suggest that cognitive tasks involving both working memory and information processing or visuospatial recognition or attention have greater impact on gait especially during the perturbed walking condition.     

Head orientation and gait stability in young adults,dancers and older adults

BackgroundControl of body orientation requires head motion detection by the vestibular system and small changes with respect to the gravitational acceleration vector could cause destabilization.Research questionWe aimed to compare the effects of different head orientations on gait stability in young adults, dancers and older adults.MethodsThree groups of 10 subjects were evaluated, the first composed of young adults (aged 18–30 years), the second composed of young healthy dancers under high performance dance training (aged 18–30 years), and the third group composed of community-dwelling older adults (aged 65–80 years). Participants walked on a treadmill at their preferred speed in four distinct head orientation conditions for four minutes each: control (neutral orientation); dynamic yaw (following a target over 45° bilaterally); up (15° neck extension), and down (40° neck flexion). Foot and trunk kinematic data were acquired using a 3D motion capture system and the gait pattern was assessed by basic gait parameters (step length, stride width and corresponding variability) and gait stability (local divergence exponents and margins of stability). Main effects of conditions and groups, as well as their interaction effects, were evaluated by repeated-measures analysis of variance.ResultsInteractions of group and head orientation were found for both step length and stride width variability; main effects of head orientation were found for all evaluated parameters and main effects of group were found for step length and its variability and local divergence exponents in all directions.SignificanceAs expected, the older adults group showed less stable gait (higher local divergence exponent), the shortest step length and greater step length variability. However, contrary to expectation, the dancers were not more stable. The yaw condition was the most challenging for all groups and the down condition seemed to be least challenging.     

The influence of net ground reaction force orientation on mediolateral stability during walking

BackgroundPrevious work has linked the eccentricity of the net ground reaction force (GRF_net) to increased mediolateral instability during single-step voluntary and compensatory stepping responses. The present work sought to understand the extent to which such control mechanisms for mediolateral stability are present during gait.Research questionHow do gait velocity and step width constraints influence the kinetic control of mediolateral stability control among healthy participants?Methods25 participants performed three walking conditions – normal walking with self-selected speed and foot-placement, fast walking with self-selected foot-placement, and narrowbase walking – across a 10-meter walkway. Lateral instability was quantified by the mediolateral margin of stability (MoS_ML). The frontal-plane eccentricity of the GRF_net was calculated as the difference between GRF_net vector orientation and that of a line joining the coordinates of COP_net and COM. Two discrete time-points (P1 and P2) following foot-contact were examined, as they have been suggested to be indicative of proactive and reactive COM control, respectively. Task-related differences in the magnitude and timing of kinematic and kinetic outcome variables were analysed using one-way ANOVAs with repeated-measures.ResultsWith constraints on step-width in narrow-base walking, participants exhibited reduced stability as evidenced by reduced MoS_ML, alongside reductions in the peak GRF_net eccentricity (θ_d) at P1. Participants exhibited no reduction in stability during fast walking, as revealed by the MoS_ML in part because of a similar onset of P1 within the gait cycle. P2 magnitude was larger in narrow-base walking relative to fast-walking, and occurred at an earlier point in the gait cycle.SignificanceFindings suggest proactive mechanisms (i.e. P1) may predominantly regulate mediolateral stability during walking. Reactive mechanisms (i.e. P2), however, may be capable of offsetting instability in situations where proactive mechanisms are insufficient.     

Effects of barefoot vs. shod walking during indoor and outdoor conditions in younger and older adults

BackgroundGait stability and variability measures in barefoot and shod locomotion are frequently investigated in younger but rarely in older adults. Moreover, most studies examine gait measures in laboratory settings instead of real-life settings.Research questionsHow are gait stability and variability parameters affected by footwear compared to barefoot walking in younger and older adults as well as under indoor vs. outdoor conditions?MethodsHealthy younger (<35 years) and older adults (>65 years) participated in the randomised within-subject study design. Participants conducted consecutive 25 m walking trials barefoot and with standardised footwear inside and outside. Inertial measurement units were mounted on the participant’s foot and used to calculate local dynamic stability (LDS), velocity and minimal toe clearance (MTC), stride length and stride time, including variabilities for these parameters. Linear mixed models were calculated.ResultsData of 32 younger (17 female, 15 male, age: 30 ± 4 years) and 42 older participants (24 female, 18 male, age: 71 ± 4 years) were analysed. MTC variability was higher in shod conditions compared to barefoot (p = 0.048) and in outdoor conditions (p < 0.001). LDS was different between age groups (p < 0.001). Gait velocity and MTC were higher in shod and outdoor conditions (both p < 0.001). Stride length and time were higher in shod conditions (both p < 0.001) and different between outdoor vs. indoor (longer stride length and shorter stride time outdoor, both (p < 0.001) as well as age groups (shorter stride length (p < 0.021) and stride time in older adults (p < 0.001).SignificanceResults suggest that gait stability and variability in older and younger adults are acutely affected by footwear vs. barefoot and indoor vs. outdoor walking conditions, indicating a high adaptiveness of these parameters to different experimental conditions. Consequently, future studies should be careful with generalising results obtained under certain conditions. Findings stress the clinical potential of barefoot walking.     

The effect of various arm and walking conditions on postural dynamic stability when recovering from a trip perturbation

BackgroundAppropriately responding to unexpected perturbations, such as a trip, is critical to sustain balance and avoid falling during walking.Research questionHow do arm motion and walking asymmetry affect postural stability when recovering from a trip perturbation?MethodsFifteen healthy young individuals, who had no experience with treadmill induced perturbations, participated in this study. The Computer-Assisted Rehabilitation Environment system (CAREN-Extended) was used to simulate unexpected perturbations while walking symmetrically and asymmetrically with various arm swings (normal, bound, released). Whole-body angular momentum (WBAM), peak trunk angular velocities, Center of Mass (COM), step width and stance time were analyzed before and when recovering from trip perturbations.ResultsParticipants were able to recover their postural stability within three strides following the sudden anterior-posterior trip perturbation. The perturbation increased peak trunk angular velocity, the COM excursion and WBAM but did not affect stance time and step width. The arm conditions had significant effects on peak trunk angular velocity, WBAM and step width during pre-perturbation. Walking conditions had a significant effect on all variables during pre-perturbation; however, post-perturbation showed significant effects only for peak trunk angular velocity, WBAM, and COM.SignificanceUnexpected perturbation had effects on most of gait variables; nevertheless, participants fully recovered and adapted their gait pattern to sudden perturbations even without using their arms while walking symmetrically and asymmetrically. Arm movements could help young individuals recover after a perturbation but are not essential for perturbations of moderate magnitude. The effect of medial-lateral perturbations on gait still need to be investigated.     

Dynamic stability during increased walking speeds is related to balance confidence of older adults: a pilot study

BackgroundSome older individuals walk slower, which may be due to decreases in mechanical stability at faster speeds or due to psychological factors like balance confidence.Research QuestionWhat is the relationship between progressively increasing walking speeds on dynamic stability in older and younger adults and how does this relationship interact with balance confidence in older adults?Methods10 young adults and 14 older adults were recruited for this pilot study. Individuals completed the Activities Specific Balance Confidence Scale. Individuals walked on a treadmill in a robotic device that interfaced with individuals at the pelvis allowing all degrees of freedom of movement and provided safety for a loss of balance. Participants walked at speeds from 0.4 - 2.0m/s in 0.2m/s increments or until the participant chose not to attempt a faster speed. Margin of stability was assessed.ResultsThe ABC of older adults was lower than younger adults (89±13 vs 99±1 scores, p=0.006) and some older adults chose to stop walking before 2.0m/s (n=6). The margin of stability variability of the older adults was significantly greater than young adults in the sagittal (p=0.013) and frontal plane (p=0.007). Older adults became unstable (margin of stability<0) at a slower speed (p<0.001). For older adults, balance confidence was correlated to the fastest speed attempted on the treadmill (rho=0.85, p<0.001). However, the balance confidence and walking speed individuals became unstable were not significantly correlated. Finally, a significant relationship was found between the zero crossing and the fastest speed attempted (rho=0.60, p=0.022).SignificanceSome older adults with lower balance confidence were less willing to experience instability at faster walking speeds on the treadmill, even though the external threat to balance was low. Lower balance confidence and a sense of loss of stability may be factors in decreased willingness to experience activities for some older adults.     

Comparable walking gait performance during executive and non-executive cognitive dual-tasks in chronic stroke: A pilot study

BackgroundFalls are a serious problem among stroke survivors due to subsequent injuries, recovery setbacks, dependence, and mortality. A growing body of dual-task (DT) studies suggests a role of executive functions in gait control and falls, particularly in subacute stroke. However, few studies have compared distinct executive and non-executive tasks, nor their effects on chronic stroke gait. Research question: The purpose of this cross-sectional study was to compare the effects of distinct working memory (2-back) and inhibition (Stroop) tasks on walking gait performance in chronic stroke survivors.MethodsA pilot sample of chronic stroke survivors (n = 11, 8 males, mean age = 70.91, 6-12months post-stroke event) and age-matched healthy controls (n = 13, 4 male; mean age = 68.46) were tested. Gait performance (speed, stride time, stride time variability, stride length and stride length variability) was measured using 2 wireless inertial measurement sensors under 4 walking conditions: 1) preferred walking (single-task: ST), 2) walking with a 2-back DT, 3) walking with a Stroop DT, and 4) walking with a non-executive motor response DT. The secondary tasks were also carried out in both ST (seated) and DT conditions, to examine bidirectional effects.ResultsWhile the stroke survivor sample had a slower gait speed across conditions and tasks, there were no significant differences between the groups [F(1, 22) = 1.13, p =.299, η²p = .049] on the spatial or temporal gait characteristics recorded: gait performance was maintained during executive and non-executive DTs. In addition, we did not find a significant effect of group on cognitive task performance (all p > .052). However, we observed a cost in accuracy on the 2-back DT for both groups, suggesting resource overlap and greater cognitive load (all t > 19.72, all p < .001).SignificanceOur gait data contradict previous studies evidencing impaired gait post-stroke, suggesting functional recovery in this chronic stroke sample.     

Reliability and validity of the protokinetics movement analysis software in measuring center of pressure during walking

Our purpose was to determine the validity and test-retest reliability of the Protokinetics Movement Analysis Software (PKMAS) in measuring center of pressure (COP) during walking as compared to a force plate gold standard. Twenty-five healthy participants (14 females, 11 males; age 20.0 ± 1.5 years) completed 2 testing sessions approximately 5 days apart (mean = 5.5 ± 1.1 days). In each session, participants completed 16 total trials across a 6 m walkway: 8 trials walking on a ProtoKinetics Zeno Walkway using PKMAS and 8 trials walking over 2 force plates arranged in an offset tandem pattern. COP path length (cm) and speed (cm/s) were calculated from data averaged across the 8 trials on a given device for a given foot. Intraclass correlation coefficients (ICC 2, k) were computed to determine between session reliability. Pearson correlation coefficients (r) and Bland-Altman plots were produced between the PKMAS and force plate outcomes for session 1 to determine validity. The PKMAS demonstrated excellent reliability (ICC 2, k ≥ 0.962) for all COP measures. Pearson correlation coefficients between PKMAS and force plates were ≥0.75 for all outcome variables. Bland-Altman plots and 95% levels of agreement revealed a bias where the PKMAS appeared to underestimate COP path length and speed by approximately 4 cm and 6 cm/s, respectively. After correcting for bias, our findings suggest the PKMAS is a reliable tool to measure COP in healthy people during gait. Using the PKMAS with the ProtoKinetics Zeno Walkway may allow for more efficient investigation of dynamic balance variables during functional movement tasks.     

The relationship between the anteroposterior and mediolateral margins of stability in able-bodied human walking

BackgroundControl of dynamic balance in human walking is essential to remain stable and can be parameterized by the margins of stability. While frontal and sagittal plane margins of stability are often studied in parallel, they may covary, where increased stability in one plane could lead to decreased stability in the other. Hypothetically, this negative covariation may lead to critically low lateral stability during step lengthening.Research questionIs there a relationship between frontal and sagittal plane margins of stability in able-bodied humans, during normal walking and imposed step lengthening?MethodsFifteen able-bodied adults walked on an instrumented treadmill in a normal walking and a step lengthening condition. During step lengthening, stepping targets were projected onto the treadmill in front of the participant to impose longer step lengths. Covariation between frontal and sagittal plane margins of stability was assessed with linear mixed-effects models for normal walking and step lengthening separately.ResultsWe found a negative covariation between frontal and sagittal plane margins of stability during normal walking, but not during step lengthening.SignificanceThese results indicate that while a decrease in anterior instability may lead to a decrease in lateral stability during normal walking, able-bodied humans can prevent lateral instability due to this covariation in critical situations, such as step lengthening. These findings improve our understanding of adaptive dynamic balance control during walking in able-bodied humans and may be utilized in further research on gait stability in pathological and aging populations.     

Dynamic walking stability of elderly people with various BMIs

BackgroundFalls are one of the major causes of injury in the elderly. Obesity may be related to the risk of falling. Understanding the dynamic stability mechanisms of obese elderly people during gait is important as it may be associated with fall protection.Research questionDoes obesity affect the dynamic walking stability of elderly people?MethodsThis is a prospective study. Fifty-three elderly participants, aged 60–82 years, were categorized into body mass index (BMI) groups. In single-limb support experiments, the center of mass velocity (COMv), center of mass acceleration (COMa), region of velocity stability (ROSv) and region of acceleration stability (ROSa) were calculated using kinematic data sampled from a motion analysis system. In addition, all participants were assessed for the dynamic balance ability test scale (DBATS). Statistical analyses were performed by one-way ANOVA, Kruskal–Wallis/Wilcoxon nonparametric tests, or bivariate Pearson/Spearman correlation analysis.ResultsDuring walking, peak COMv and COMa decreased with increasing BMI (Normal BMI: 1.20 ± 0.14 m/s, 1.66 ± 0.36 m/s²; High BMI: 1.14 ± 0.11 m/s, 1.56 ± 0.30 m/s²; Higher BMI: 1.04 ± 0.15 m/s, 1.47 ± 0.25 m/s²). At toe-off (TO), the normalized participants’ center of mass (COM) is significantly more anterior in the Higher BMI group (Normal BMI: -0.30 ± 0.09, High BMI: -0.23 ± 0.07, Higher BMI: -0.16 ± 0.10), their normalized COMv and COMa (Normal BMI: 1.40 ± 0.16, 0.53 ± 0.11; High BMI: 1.33 ± 0.13, 0.49 ± 0.11; Higher BMI: 1.21 ± 0.16, 0.46 ± 0.11) are slower. The mean DBATS score of the Higher BMI group was the highest, indicating the weakest dynamic balance ability.SignificanceThe COM dynamic stability parameters indicate that obesity may worsen balance, with the peak COMv and ROSv most affected. With increasing BMI, the dynamic stability and balance of elderly people both decreased.     

Center of mass in analysis of dynamic stability during gait following stroke: A systematic review

BackgroundThe Center of mass (CoM) analysis reveals important aspects of gait dynamic stability of stroke patients, but the variety of methods and measures represents a challenge for planning new studies.Research questionHow have the CoM measures been calculated and employed to investigate gait stability after a stroke? Three issues were addressed: (i) the methodological aspects of the calculation of CoM measures; (ii) the purposes and (iii) the conclusions of the studies on gait stability that employed those measures.MethodsPubMed and Science Direct databases have been searched to collect original articles produced until July 2017. A set of 26 studies were selected according to criteria involving their methodological quality.ResultsA compromise between accuracy and feasibility in CoM calculation could be reached using the segmental method with 7–9 segments. Regarding their purposes, two types of studies were identified: clinical and research oriented. From the first ones, we highlighted: the margin of stability (MoS) in the mediolateral (ML) direction, and the angular momentum in the frontal plane could be indicators of dynamical stability; the MoS in the anteroposterior (AP) direction might be able to detect the risk of falls and the symmetry of vertical CoM displacement could be used to analyze energy expenditure during gait. These and other CoM measures are potentially useful in clinical settings, but their psychometric properties are still to be determined. The research oriented studies allowed to clarify that stability is not improved by widening the step in stroke patients and that the impaired control of the non-paretic limb might be the main source of instability.SignificanceThis review provides recommendations on the methods for estimating CoM and its measures, identifies the potential usefulness of CoM parameters and indicates issues that could be addressed in future studies.     

Upper body accelerations during walking in healthy young and elderly men

The purpose of the present study was to assess whether any differences existed in the upper body accelerations of young and elderly subjects during natural speed walking. Head and trunk accelerations in eight young subjects (aged 23±4 years) and eight healthy elderly subjects (aged 74±3 years) were measured during level walking on a 20 m walkway using a pair of tri-axial accelerometers. Heel contact and toe-off events were determined using a footswitch system embedded in the innersole of the right shoe. Gait measures assessed included; stride, stance and swing durations, cadence, gait velocity, step length and 3D head and trunk accelerations. All acceleration variables were normalised to walking speed before statistical analysis. The main findings of this study were: (1) the peak positive anterior–posterior (AP) trunk acceleration associated with push-off was significantly lower for elderly subjects, (2) the peak negative AP head and trunk accelerations following heel contact was significantly higher for elderly subjects, and (3) the time delay between trunk and head accelerations experienced in the AP direction was significantly lower for the elderly compared to the young group. Together, these results suggest that elderly subjects exhibit different patterns of upper body motion in the direction of travel compared to younger subjects. These differences are probably motivated by the need to maximise dynamic stability during critical parts of the gait cycle.