Muscle contributions to frontal plane angular momentum during walking

Modelling strategies supplemental to foot placement for frontal-plane stability in walking

Walking is unstable and requires active control. Foot placement is the primary strategy to maintain frontal-plane balance with contributions from lateral ankle torques, ankle push-off and trunk postural adjustments. Because these strategies interact, their individual contributions are difficult to study. Here, we used computational modelling to understand these individual contributions to frontal-plane walking balance control. A three-dimensional bipedal model was developed based on linear inverted pendulum dynamics. The model included controllers that implement the stabilization strategies seen in human walking. The control parameters were optimized to mimic human gait biomechanics for typical spatio-temporal parameters during steady-state walking and when perturbed by mediolateral ground shifts. Using the optimized model as a starting point, the contributions of each stabilization strategy were explored by progressively removing strategies. The lateral ankle and trunk strategies were more important than ankle push-off, with their removal causing up to 20% worse balance recovery compared with the full model, while removing ankle push-off led to minimal changes. Our results imply a potential benefit of preferentially training these strategies in populations with poor balance. Moreover, the proposed model could be used in future work to investigate how walking stability may be preserved in conditions reflective of injury or disease.

Direct biomechanical manipulation of human gait stability: A systematic review

People fall more often when their gait stability is reduced. Gait stability can be directly manipulated by exerting forces or moments onto a person, ranging from simple walking sticks to complex wearable robotics. A systematic review of the literature was performed to determine: What is the level of evidence for different types of mechanical manipulations on improving gait stability? The study was registered at PROSPERO (CRD42020180631). Databases Embase, Medline All, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, and Google Scholar were searched. The final search was conducted on the 1st of December, 2022. The included studies contained mechanical devices that influence gait stability for both impaired and non-impaired subjects. Studies performed with prosthetic devices, passive orthoses, and analysing post-training effects were excluded. An adapted NIH quality assessment tool was used to assess the study quality and risk of bias. Studies were grouped based on the type of device, point of application, and direction of forces and moments. For each device type, a best-evidence synthesis was performed to quantify the level of evidence based on the type of validity of the reported outcome measures and the study quality assessment score. Impaired and non-impaired study participants were considered separately. From a total of 4701 papers, 53 were included in our analysis. For impaired subjects, indicative evidence was found for medio-lateral pelvis stabilisation for improving gait stability, while limited evidence was found for hip joint assistance and canes. For non-impaired subjects, moderate evidence was found for medio-lateral pelvis stabilisation and limited evidence for body weight support. For all other device types, either indicative or insufficient evidence was found for improving gait stability. Our findings also highlight the lack of consensus on outcome measures amongst studies of devices focused on manipulating gait.

The effects of plantarflexor weakness and reduced tendon stiffness with aging on gait stability

Falls among older adults are a costly public health concern. Such falls can be precipitated by balance disturbances, after which a recovery strategy requiring rapid, high force outputs is necessary. Sarcopenia among older adults likely diminishes their ability to produce the forces necessary to arrest gait instability. Age-related changes to tendon stiffness may also delay muscle stretch and afferent feedback and decrease force transmission, worsening fall outcomes. However, the association between muscle strength, tendon stiffness, and gait instability is not well established. Given the ankle's proximity to the onset of many walking balance disturbances, we examined the relation between both plantarflexor strength and Achilles tendon stiffness with walking-related instability during perturbed gait in older and younger adults-the latter quantified herein using margins of stability and whole-body angular momentum including the application of treadmill-induced slip perturbations. Older and younger adults did not differ in plantarflexor strength, but Achilles tendon stiffness was lower in older adults. Among older adults, plantarflexor weakness associated with greater whole-body angular momentum following treadmill-induced slip perturbations. Weaker older adults also appeared to walk and recover from treadmill-induced slip perturbations with more caution. This study highlights the role of plantarflexor strength and Achilles tendon stiffness in regulating lateral gait stability in older adults, which may be targets for training protocols seeking to minimize fall risk and injury severity.

Effect of crutch and walking-boot use on whole-body angular momentum during gait

Crutches are the most prescribed ambulatory assistive device and are used for mobility and maintaining weight-bearing restrictions after injury or surgery. However, standard axillary crutches (SACs) can lead to overuse and other injuries and restrict upper limb movement. Hands-free crutches (HFC) do not restrict upper limb movement but their effect on balance control, with or without commonly prescribed walking boots, is poorly understood. The purpose of this study was to compare the effect of crutch type (SACs vs. HFC) and boot use on whole-body angular momentum (RAM), a measure of balance control. Participant's balance confidence, pain, comfort, and device preference were assessed. Seventeen participants were evaluated while walking without a crutch (NONE), with SACs, and with an HFC, and walked with and without a walking boot in each crutch condition. The gait pattern used with SACs resulted in significantly greater limb angular velocity (p < .05), and an 84% increase in RAM (p < .001) as compared to the HFC. There were no differences between the SAC and HFC for balance confidence, pain, or comfort, however most (71.1%) participants preferred the HFCs. These results suggest that individuals can better control angular momentum with the HFCs and thus may be less susceptible to loss of balance.

Lower limb vertical stiffness and frontal plane angular impulse during perturbation-induced single limb stance and their associations with gait in individuals post-stroke

After stroke, deficits in paretic single limb stance (SLS) are commonly observed and affect walking performance. During SLS, the hip abductor musculature is critical in providing vertical support and regulating balance. Although disrupted paretic hip abduction torque production has been identified in individuals post-stroke, interpretation of previous results is limited due to the discrepancies in weight-bearing conditions. Using a novel perturbation-based assessment that could induce SLS by removing the support surface underneath one limb, we aim to investigate whether deficits in hip abduction torque production, vertical body support, and balance regulation remain detectable during SLS when controlling for weight-bearing, and whether these measures are associated with gait performance. Our results showed that during the perturbation-induced SLS, individuals post-stroke had lower hip abduction torque, less vertical stiffness, and increased frontal plane angular impulse at the paretic limb compared to the non-paretic limb, while no differences were found between the paretic limb and healthy controls. In addition, vertical stiffness during perturbation-induced SLS was positively correlated with single support duration during gait at the paretic limb and predicted self-selected and fast walking speeds in individuals post-stroke. The findings indicate that reduced paretic hip abduction torque during SLS likely affects vertical support and balance control. Enhancing SLS hip abduction torque production could be an important rehabilitation target to improve walking function for individuals post-stroke.

Lower-limb joint quasi-stiffness in the frontal and sagittal planes during walking at different step widths

Quasi-stiffness describes the intersegmental joint moment-angle relationship throughout the progression of a task. Previous work has explored sagittal-plane ankle quasi-stiffness and its application for the development of powered lower-limb assistive devices. However, frontal-plane quasi-stiffness remains largely unexplored but has important implications for the development of exoskeletons since clinical populations often walk with wider steps and rely on frontal-plane balance recovery strategies at the hip and ankle. This study aimed to characterize frontal-plane hip and ankle quasi-stiffness during walking and determine how step width affects quasi-stiffness in both the frontal and sagittal planes. Kinematic and kinetic data were collected and quasi-stiffness values computed for healthy young adults (n = 15) during treadmill walking across a range of step widths. We identified specific subphases of the gait cycle that exhibit linear and quadratic frontal-plane quasi-stiffness approximations for the hip and ankle, respectively. In addition, we found that at wider step widths, sagittal-plane ankle quasi-stiffness increased during early stance (∼12-35% gait cycle), sagittal-plane hip quasi-stiffness decreased in late stance (∼40-55% gait cycle) and frontal-plane hip quasi-stiffness decreased during terminal stance (∼48-65% gait cycle). These results provide a framework for further exploration of frontal-plane quasi-stiffness, lend insight into how quasi-stiffness may relate to balance control at various step widths, and motivate the development of stiffness-modulating assistive devices to improve balance related outcomes.

Plantar somatosensory restoration enhances gait, speed perception, and motor adaptation

Lower limb loss is a major insult to the body's nervous and musculoskeletal systems. Despite technological advances in prosthesis design, artificial limbs are not yet integrated into the body's physiological systems. Therefore, lower limb amputees (LLAs) experience lower balance confidence, higher fear of falls, and impaired gait compared with their able-bodied peers (ABs). Previous studies have demonstrated that restored sensations perceived as originating directly from the missing limb via neural interfaces improve balance and performance in certain ambulatory tasks; however, the effects of such evoked sensations on neural circuitries involved in the locomotor activity are not well understood. In this work, we investigated the effects of plantar sensation elicited by peripheral nerve stimulation delivered by multicontact nerve cuff electrodes on gait symmetry and stability, speed perception, and motor adaptation. We found that restored plantar sensation increased stance time and propulsive force on the prosthetic side, improved gait symmetry, and yielded an enhanced perception of prosthetic limb movement. Our results show that the locomotor adaptation among LLAs with plantar sensation became similar to that of ABs. These findings suggest that our peripheral nerve-based approach to elicit plantar sensation directly affects central nervous pathways involved in locomotion and motor adaptation during walking. Our neuroprosthesis provided a unique model to investigate the role of somatosensation in the lower limb during walking and its effects on perceptual recalibration after a locomotor adaptation task. Furthermore, we demonstrated how plantar sensation in LLAs could effectively increase mobility, improve walking dynamics, and possibly reduce fall risks.

The influence of step width on balance control and response strategies during perturbed walking in healthy young adults

Individuals with neuromuscular deficits often walk with wider step widths compared to healthy adults. Wider steps have been linked to a higher destabilizing frontal-plane external moment and greater range of frontal-plane whole-body angular momentum (HR), which is an indicator of decreased balance control. The purpose of this study was to experimentally determine 1) how step width alters balance control during steady-state walking, and 2) if step width changes the balance response strategies following mediolateral surface perturbations in healthy adults. Fifteen healthy young adults (7 male, age: 25 ± 4 years) walked on an instrumented treadmill at narrow, self-selected, wide and extra-wide step widths. During perturbed trials, the treadmill provided random mediolateral surface translations to each foot midway through single-leg-stance. Muscle electromyography, biomechanical measures (HR, frontal-plane external moment and joint moments) and deviations (differences in these measures between the perturbed and unperturbed walking trials) were compared across step widths. During steady state walking, wider steps were associated with decreased balance control. Increasing step widths were also associated with increased gluteus medius activity and reduced hip abduction and ankle inversion moments, which suggests healthy subjects rely more on a lateral ankle strategy to maintain balance at increasing step widths. There was no change in the plantarflexion moment. During perturbed walking, lateral, but not medial, surface translations adversely affected balance control. Further, wider steps did not change the balance response strategies following the perturbations, which suggests healthy individuals have the capacity to respond similarly to the perturbations at different step widths.

Lower Limb Vertical Stiffness and Frontal Plane Angular Impulse during Perturbation-Induced Single Limb Stance and Their Associations with Gait in Individuals Post-Stroke

Background

After stroke, deficits in paretic single limb stance (SLS) are commonly observed and affect walking performance. During SLS, the hip abductor musculature is critical in providing vertical support and regulating balance. Although disrupted paretic hip abduction torque production has been identified in individuals post-stroke, interpretation of previous results is limited due to the discrepancies in weight-bearing conditions.

Objective

To investigate whether deficits in hip abduction torque production, vertical body support, and balance regulation remain during SLS when controlling for weight-bearing using a perturbation-based assessment, and whether these measures are associated with gait performance.

Methods

We compared hip abduction torque, vertical stiffness, and frontal plane angular impulse between individuals post-stroke and healthy controls when SLS was induced by removing the support surface underneath one limb. We also tested for correlations between vertical stiffness and angular impulse during perturbation-induced SLS and gait parameters during overground walking.

Results

During the perturbation-induced SLS, lower hip abduction torque, less vertical stiffness, and increased frontal plane angular impulse were observed at the paretic limb compared to the non-paretic limb, while no differences were found between the paretic limb and healthy controls. Vertical stiffness during perturbation-induced SLS was positively correlated with single support duration during gait at the paretic limb and predicted self-selected and fast walking speeds in individuals post-stroke.

Conclusions

Reduced paretic hip abduction torque during SLS likely affects vertical support and balance control. Enhancing SLS hip abduction torque production could be an important rehabilitation target to improve walking function for individuals post-stroke.

Dynamic stability during level walking and obstacle crossing in children aged 2–5 years estimated by marker-less motion capture

In the present study, dynamic stability during level walking and obstacle crossing in typically developing children aged 2–5 years (n = 13) and healthy young adults (n = 19) was investigated. The participants were asked to walk along unobstructed and obstructed walkways. The height of the obstacle was set at 10% of the leg length. Gait motion was captured by three RGB cameras. 2D body landmarks were estimated using OpenPose, a marker-less motion capture algorithm, and converted to 3D using direct linear transformation (DLT). Dynamic stability was evaluated using the margin of stability (MoS) in the forward and lateral directions. All the participants successfully crossed the obstacles. Younger children crossed the obstacle more carefully to avoid falls, as evidenced by obviously decreased gait speed just before the obstacle in 2-year-olds and the increased in maximum toe height with younger age. There was no significant difference in the MoS at the instant of heel contact between children and adults during level walking and obstacle crossing in the forward direction, although children increased the step length of the lead leg to a greater extent than the adults to ensure base of support (BoS)-center of mass (CoM) distance. In the lateral direction, children exhibited a greater MoS than adults during level walking [children: 9.5%, adults: 6.5%, median, W = 39.000, p &lt; .001, rank-biserial correlation = −0.684]; however, some children exhibited a smaller MoS during obstacle crossing [lead leg: −5.9% to 3.6% (min–max) for 4 children, 4.7%–6.4% [95% confidence interval (CI)] for adults, p &lt; 0.05; trail leg: 0.1%–4.4% (min–max) for 4 children, 4.7%–6.4% (95% CI) for adults, p &lt; 0.05]]. These results indicate that in early childhood, locomotor adjustment needed to avoid contact with obstacles can be observed, whereas lateral dynamic stability is frangible.

Extensive and Differential Deterioration of Hip Muscles May Preexist in Older Adults with Hip Fractures: Evidence from a Cross-Sectional Study

Hip muscles play an increasingly important role in lower limb function with aging. Investigating the deterioration of hip muscles and its relationship with hip fracture (HF) may help identify older adults prone to fall. In this study, patients with fall-related HF within 48 h and non-fracture controls aged ≥ 60 years were enrolled. The cross-sectional area (size) and attenuation (density) of the hip flexors, extensors, adductors, and abductors were calculated after segmentation on computed tomography images. The correlation of muscle parameters with HF and age were evaluated using logistic and multiple regression, respectively. Discrimination of HF was analyzed by receiver-operating characteristic analyses. A total of 220 patients and 91 controls were included. The size of the flexors, extensors, and abductors, and the density of the flexors, adductors, and abductors were lower in patients with HF after adjustment for sex, age, and body mass index (BMI). However, decreased muscle size was only observed in hip extensors in patients aged 60-74 years. Decreased muscle size was associated with HF independent of sex, age, BMI, and hip trabecular bone mineral density. Abductor size exhibited a significantly larger negative correlation with age in patients compared to controls. Including abductor size or all muscle size was effective for discrimination of HF in patients aged ≥ 75 years. In conclusion, older adults with HF may have sustained extensive and differential hip muscle deterioration before the injury; extensor atrophy in younger-old age and consideration of a closer relationship between abductor size and age deserve attention.

Spatiotemporal parameters during turning gait maneuvers of different amplitudes in young and elderly healthy adults: A descriptive and comparative study

BACKGROUND

Turning during walking adds complexity to gait and has been little investigated until now. Research question What are the differences in spatiotemporal parameters between young and elderly healthy adults performing quarter-turns (90°), half-turns (180°) and full-turns (360°)?

METHODS

The spatiotemporal parameters of 10 young and 10 elderly adults were recorded in a laboratory while turning at 90°, 180° and 360°. Two-way mixed ANOVA were performed to determine the effect of age and turning amplitude.

RESULTS

Elderly were slower and needed more steps and time to perform turns of larger amplitude than young adults. Cadence did not differ across age or across turning amplitude. Generally, in the elderly, the spatial parameters were smaller and the temporal parameters enhancing stability (i.e., double-support phase and stance/cycle ratio) were larger, especially for turns of larger amplitudes. In elderly adults, the variability of some spatial parameters was decreased, whereas the variability of some temporal parameters was increased. Stride width of the external leg showed the most substantial difference between groups. Most parameters differed between turning at 90° and turning at larger amplitudes (180°, 360°). Significance This study extends the characterization of turning biomechanics with respect to ageing. It also suggested paying particular attention to the turning amplitude. Finally, the age-related differences may pave the way for new selective rehabilitation protocols in the elderly.

Determinants and Characterization of Locomotion in Adults with Late-Onset Pompe Disease: New Clinical Biomarkers

BACKGROUND

The late-onset form of Pompe disease (LOPD) is characterized by muscle weakness, locomotor limitations and a risk of falls. The mechanisms responsible for altered locomotion in adults with LOPD are unknown. The identification of clinical biomarkers is essential for clinical follow-up and research.

OBJECTIVES

To identify muscle determinants of impaired locomotor performance, gait stability and gait pattern, and biomechanical determinants of falls in adults with LOPD.

METHODS

In this cross-sectional, case-control study, LOPD and control participants underwent 3D gait analysis, locomotor performance tests and muscle strength measurements (isokinetic dynamometer). We explored the muscular determinants of locomotor performance (gait speed, 6-minute walk test distance and timed up and go test), gait stability (spatiotemporal gait variables) and the gait pattern. We also explored biomechanical gait determinants of falls. After intergroup comparisons, determinants were sought to use forward stepwise multiple regression.

RESULTS

Eighteen participants with LOPD and 20 control participants were included. Locomotor performance, gait stability, and the gait pattern were significantly altered in LOPD compared to control participants. Hip abductor strength was the main common determinant of locomotor performance, gait stability and pelvic instability. Hip flexor strength was the main determinant of abnormal gait kinematics at the hip and knee. Percentage duration of single support phase during the gait cycle was the main determinant of falls.

CONCLUSIONS

Hip abductor strength and percentage duration of single support during gait were the major determinants of locomotor performance, gait stability, falls and the gait pattern in LOPD. These new clinical biomarkers should therefore be systematically assessed using instrumented tools to improve the follow-up of adults with LOPD. They should also be considered in future studies to accurately assess the effects of new therapies. Hip abductor strength and single support phase should also be priority targets for rehabilitation.

Locomotion control during curb descent: Bilateral ground reaction variables covary consistently during the double support phase regardless of future foot placement constraints

During community ambulation, anticipatory adaptations in gait are key for navigating built, populated and natural environments. It has been argued that some instability in gait can be functionally beneficial in situations demanding high maneuverability, and while the mechanisms utilized to maintain locomotor balance are well understood, relatively less is known about how the control of gait stability changes to facilitate upcoming maneuvers in challenging environments. The double support phase may be important in this regard; since both feet can push off the ground simultaneously, there is greater control authority over the body's movement during this phase. Our goal was to identify how this control authority is exploited to prepare for upcoming maneuvers in challenging environments. We used synergy indices to quantify the degree of coordination between the ground reaction forces and moments under the two feet for stabilizing the resultant force and moment on the body during the double support phase of curb descent. In contrast to our expectations, we observed that the kinetic synergy indices during curb descent were minimally influenced by expected foot targeting maneuvers for the subsequent step. Only the resultant moment in the frontal plane showed reduced stability when targeting was required, but the synergy index was still high, indicating that the resultant moment was stable. Furthermore, the synergy indices indicated that the main function of the ground reaction variables is to maintain stability of whole-body rotations during double support, and this prerogative was minimally influenced by the subsequent foot targeting tasks, likely because the cost of losing balance while descending a curb would be higher than the cost of mis-stepping on a visual target. Our work demonstrates the salience of stabilizing body rotations during curb negotiation and improves our understanding of locomotor control in challenging environments.

Regulation of whole-body and segmental angular momentum in persons with Parkinson's disease on an irregular surface

BACKGROUND

Persons with Parkinson's disease have impaired motor control that increases their chance of falling when walking, especially on difficult terrains. This study investigated how persons with Parkinson's disease regulate their dynamic balance on a regular and an irregular surface.

METHODS

Nine participants with Parkinson's disease and nine healthy, age-matched control participants ambulated on both a regular and an irregular surface. Whole-body and segmental angular momenta were calculated using three-dimensional motion capture data. Major modes of variability between health groups on the two surfaces were investigated using principal component analysis, while differences within each health group between surfaces was investigated using statistical parametric mapping t-tests.

FINDINGS

Between groups, the Parkinson participants had greater sagittal, frontal, and transverse whole-body angular momentum on both surfaces, primarily following heel-strike, and the magnitude difference on the irregular surface was greater than on the regular surface. The greatest between group segmental differences on the irregular compared to the regular surface were the legs in the sagittal plane and the head/trunk/pelvis in the transverse plane, with the Parkinson group having greater magnitudes. The within-group comparison found the Parkinson participants had poorer regulation of whole-body angular momentum in the sagittal plane, while the healthy participants showed no consistent differences between surfaces.

INTERPRETATION

On an irregular surface, persons with Parkinson's disease exhibit poor control of dynamic balance in the frontal and sagittal planes. These results emphasize the need for weight transfer techniques and training in both the sagittal and frontal planes to maximize balance and reduce fall risk.

Changes in dynamic balance control in adults with obesity across walking speeds

Adults with obesity have gait instability, leading to increased fall risks and decreased physical activity. Whole-body angular momentum (WBAM) is regulated over a gait cycle, essential to avoid a fall. However, how obese adults regulate WBAM during walking is unknown. The current study investigated changes in WBAM about the body's center of mass (COM) during walking in obese and non-obese adults across different walking speeds. Twenty-eight young adults with obesity and normal weight walked barefoot at a fixed walking speed (FWS, 1.25 m/s) and at five different speeds based on their preferred walking speed (PWS): 50, 75, 100, 125, and 150 % of PWS. Adults with obesity walked slower with shorter step length, wider step width, and longer double support time (p < 0.01). The ranges of frontal- and transverse-plane WBAM were greater in obese adults (p < 0.01). We also found that the range of frontal-plane WBAM did not significantly change with walking speed (p > 0.05), while the range of transverse-plane WBAM increased with walking speed (p < 0.01). The ranges of frontal- and transverse-plane WBAM increased with the mediolateral ground reaction force and mediolateral moment arm (p < 0.01), which may be most affected by lateral foot placement relative to the body's COM. Our findings suggest that controlling mediolateral stability during walking is more challenging in obese adults, independent of their slow walking speed. Understanding whole-body rotational dynamics observed in obese walking provides an insight into the biomechanical link between obesity and gait instability, which may help find a way to reduce fall risks and increase physical activity.

Effects of age on dynamic balance measures and their correlation during walking across the adult lifespan

In this study, we aimed to discover (1) the effects of age on dynamic balance measures, including the margin of stability (MOS), whole-body angular momentum (H), and misalignment of the desired and measured centers of pressure (dCOP and mCOP, respectively) in the anteroposterior (AP) and mediolateral (ML) directions, (2) the relationship between gait parameters and these balance measures, and (3) the relationships between these balance measures. We used the kinetic and kinematic data of 151 participants aged 20–77 years from a publicly available database. Participants were divided into three groups: young, middle-aged, and old. The step width of the old group was higher than that of the young group. Age-related differences in dynamic measures were found in the ML direction and not in the AP direction: MOS, peak-to-peak range of H, and dCOP–mCOP in the old group were greater than in the young group. ML MOS positively correlated with the frontal peak-to-peak range of H. The ML peak-to-peak range of H positively correlated with ML dCOP–mCOP across the adult lifespan. Our findings provide new insights for understanding the effects of age on dynamic balance and the relationships between the metrics. Older adults walked with a larger step width, resulting in a large stability margin in the ML direction, although with increased moment and momentum around the center of mass in the frontal plane.

Improvement in gait stability in older adults after ten sessions of standing balance training

Balance training aims to improve balance and transfer acquired skills to real-life tasks. How older adults adapt gait to different conditions, and whether these adaptations are altered by balance training, remains unclear. We hypothesized that reorganization of modular control of muscle activity is a mechanism underlying adaptation of gait to training and environmental constraints. We investigated the transfer of standing balance training, shown to enhance unipedal balance control, to gait and adaptations in neuromuscular control of gait between normal and narrow-base walking in twenty-two older adults (72.6 ± 4.2 years). At baseline, after one, and after ten training sessions, kinematics and EMG of normal and narrow-base treadmill walking were measured. Gait parameters and temporal activation profiles of five muscle synergies were compared between time-points and gait conditions. Effects of balance training and an interaction between training and gait condition on step width were found, but not on synergies. After ten training sessions step width decreased in narrow-base walking, while step width variability decreased in both conditions. Trunk center of mass displacement and velocity, and the local divergence exponent, were lower in narrow-base compared to normal walking. Activation duration in narrow-base compared to normal walking was shorter for synergies associated with dominant leg weight acceptance and non-dominant leg stance, and longer for the synergy associated with non-dominant heel-strike. Time of peak activation associated with dominant leg stance occurred earlier in narrow-base compared to normal walking, while it was delayed in synergies associated with heel-strikes and non-dominant leg stance. The adaptations of synergies to narrow-base walking may be interpreted as related to more cautious weight transfer to the new stance leg and enhanced control over center of mass movement in the stance phase. The improvement of gait stability due to standing balance training is promising for less mobile older adults.

Individual muscle responses to mediolateral foot placement perturbations during walking

Walking requires active control of frontal plane balance through adjustments to mediolateral foot placement and ground reaction forces. Previous work on mediolateral balance perturbations and control of foot placement has often focused on the bilateral gluteus medius muscles. However, additional leg and trunk muscles can influence foot placement by transferring power to the foot and pelvis during swing. Thus, the purpose of this study was to determine individual muscle contributions to balance control following medial and lateral foot placement perturbations. Ten participants performed treadmill walking trials which included perturbations immediately before randomized heel strikes. Muscle contributions to foot placement, ground reaction forces, trunk power and frontal plane external moments during representative perturbed and unperturbed gait cycles were estimated using musculoskeletal modeling and simulation. Net muscle contributions to foot placement were 61 ± 50% more medial during the first recovery step following lateral perturbations and 28 ± 14% less medial in the second recovery step following medial perturbations. Following lateral perturbations, the swing gluteus medius performed 57 ± 50% more lateral work and the stance gluteus medius performed 61 ± 50% more medial work on the foot. Following medial perturbations, the erector spinae performed 39 ± 33% less lateral work on the foot. Changes in net muscle work on the foot were inconsistent with changes in step width, suggesting that changes in step width were not due to active muscle control but rather the mechanical effect of the perturbation. These outcomes provide a foundation for future studies analyzing balance control in populations at risk of falling.

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

BACKGROUND

Individuals 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 PURPOSE

To investigate the change in angular momentum about the body's COM during walking in individuals with different degrees of obesity.

METHODS

Thirty-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.

RESULTS

We 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).

SIGNIFICANCE

Obesity 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.

Differences in balance control between healthy younger and older adults during steady-state walking

Each year approximately one third of older adults fall and experience extensive musculoskeletal injuries and functional disabilities. An important element in maintaining dynamic balance is the regulation of whole-body angular momentum, which is achieved by proper foot placement with respect to the body center-of-mass as well as generation of appropriate ground reaction forces. Analyzing these quantities in younger and older adults may provide insight into differences in their underlying mechanics for maintaining dynamic balance. This study examined three-dimensional whole-body angular momentum in 13 healthy older (71.8 ± 8.3 years) and 9 younger (23.2 ± 2.8 years) adults walking at their self-selected and fastest-comfortable speeds. The older adults had a significantly higher range of frontal-plane angular momentum compared to the younger adults at both speeds, suggesting poorer mediolateral balance control. This difference was related to the older adults having a wider foot placement with respect to the body center-of-mass, which when combined with the vertical ground reaction force, created a higher destabilizing external moment during single-limb stance that acts to rotate the body towards the contralateral swing leg. To counteract this destabilizing moment, the older adults generated a higher hip abduction moment. There were no differences in the range of sagittal- and transverse-plane angular momentum between age groups at either speed. These results suggest that control of dynamic balance in the frontal-plane is more challenging than in the sagittal-plane for older adults and highlight the importance of proper weight transfer mechanisms and hip abductor force production for maintaining mediolateral balance during walking.

A Predictive Framework to Provide Neuromuscular Insights in Reshaping Dynamic Balance during Transient Locomotion

Anticipated and unanticipated directional changes are commonplace in daily lives. The need for dynamic balance is amplified when these transitions are performed in an unplanned (i.e., unanticipated) manner. In this study, we used predictive simulations and optimal control constructs to test a method for reshaping dynamic balance of unanticipated crossover cuts. We also compare how such improvements can be mediated at the musculotendon level. Our study shows that the performance of unanticipated crossover cuts can be optimized to improve dynamic balance, and highlight the potential for predictive simulations and optimal control to provide quantitative targets for reshaping dynamic balance in unanticipated crossover cuts-targets which are biologically-feasible.Clinical Relevance-This approach could inform task-specific rehabilitation therapy by suggesting how to reshape an individual's dynamic balance and which joint-level kinematic adjustments and muscle groups would be optimal to engage in doing so.

Stabilization demands of walking modulate the vestibular contributions to gait

Stable walking relies critically on motor responses to signals of head motion provided by the vestibular system, which are phase-dependent and modulated differently within each muscle. It is unclear, however, whether these vestibular contributions also vary according to the stability of the walking task. Here we investigate how vestibular signals influence muscles relevant for gait stability (medial gastrocnemius, gluteus medius and erector spinae)-as well as their net effect on ground reaction forces-while humans walked normally, with mediolateral stabilization, wide and narrow steps. We estimated local dynamic stability of trunk kinematics together with coherence of electrical vestibular stimulation (EVS) with muscle activity and mediolateral ground reaction forces. Walking with external stabilization increased local dynamic stability and decreased coherence between EVS and all muscles/forces compared to normal walking. Wide-base walking also decreased vestibulomotor coherence, though local dynamic stability did not differ. Conversely, narrow-base walking increased local dynamic stability, but produced muscle-specific increases and decreases in coherence that resulted in a net increase in vestibulomotor coherence with ground reaction forces. Overall, our results show that while vestibular contributions may vary with gait stability, they more critically depend on the stabilization demands (i.e. control effort) needed to maintain a stable walking pattern.

Basic Spatiotemporal Gait Variables of Young and Older Healthy Volunteers Walking Along a Novel Figure-of-8 Path

Background: Locomotion along curved trajectories requires fine coordination among body segments. Elderly people may adopt a cautious attitude when steering. A simple, expeditious, patient-friendly walking protocol can be a tool to help clinicians. We evaluated the feasibility of a procedure based upon a newly designed Figure-of-eight (nFo8) path and an easy measurement operation. Methods: Sixty healthy volunteers, aged from 20 to 86 years, walked three times at self-selected speed along a 20 m linear (LIN) and the 20 m nFo8 path. Number of steps, mean speed and walk ratio (step length/cadence) were collected. Data were analysed for the entire cohort and for the groups aged 20-45, 46-65, and >65 years. Results: There was no difference in mean LIN walking speed between the two younger groups but the oldest was slower. During nFo8, all groups were slower (about 16%) than during LIN. Cadence was not different across groups but lower during nFo8 in each group. Step length was about 8% shorter in the two younger groups and 14% shorter in the oldest during nFo8 compared to LIN. Walk ratio was the smallest in the oldest group for both LIN and nFo8. Conclusions: A complex nFo8 walking path, with fast and easy measurement of a simple set of variables, detects significant differences with moderate and large effects in gait variables in people >65 years. This challenging trajectory is more revealing than LIN. Further studies are needed to develop a quick clinical tool for assessment of gait conditions or outcome of rehabilitative treatments.

Biomechanical response to mediolateral foot-placement perturbations during walking

Dynamic balance in the frontal plane requires active control, which is accomplished largely through control of mediolateral foot placement. Individuals without mobility impairments have the ability to compensate for variability in foot-placement to maintain their balance; however, it is unknown how individuals respond to unexpected mediolateral perturbations to their foot placement that alter their balance control. The purpose of this study was to identify the biomechanical responses of individuals without mobility impairments to medial and lateral foot-placement perturbations during walking. Three-dimensional body segment kinematic and ground reaction force data were collected from 15 participants at 1.0 m/s and their self-selected speed on an instrumented treadmill. Dynamic balance was assessed by analyzing whole-body angular momentum in the frontal plane. We hypothesized that participants would respond to the perturbations with a combination of a lateral ankle strategy, hip adduction strategy and/or ankle push-off strategy to restore their balance. Overall, the medial perturbations adversely affected dynamic balance while lateral perturbations had little effect. Individuals responded to medial (lateral) perturbations with an increased (decreased) ankle inversion moment, which correlated to lateral (medial) shifts in their foot center of pressure. In addition, individuals responded to medial (lateral) perturbations with a decreased (slightly decreased) hip abduction moment. Contrary to our hypothesis, we did not observe an ankle push-off moment response but rather, a small response in the opposite direction. These results highlight the response of individuals without mobility impairments to unexpected foot-placement perturbations and provide a basis of comparison for those with impaired balance control.

Active foot placement control ensures stable gait: Effect of constraints on foot placement and ankle moments

Step-by-step foot placement control, relative to the center of mass (CoM) kinematic state, is generally considered a dominant mechanism for maintenance of gait stability. By adequate (mediolateral) positioning of the center of pressure with respect to the CoM, the ground reaction force generates a moment that prevents falling. In healthy individuals, foot placement is complemented mainly by ankle moment control ensuring stability. To evaluate possible compensatory relationships between step-by-step foot placement and complementary ankle moments, we investigated the degree of (active) foot placement control during steady-state walking, and under either foot placement-, or ankle moment constraints. Thirty healthy participants walked on a treadmill, while full-body kinematics, ground reaction forces and EMG activities were recorded. As a replication of earlier findings, we first showed step-by-step foot placement is associated with preceding CoM state and hip ab-/adductor activity during steady-state walking. Tight control of foot placement appears to be important at normal walking speed because there was a limited change in the degree of foot placement control despite the presence of a foot placement constraint. At slow speed, the degree of foot placement control decreased substantially, suggesting that tight control of foot placement is less essential when walking slowly. Step-by-step foot placement control was not tightened to compensate for constrained ankle moments. Instead compensation was achieved through increases in step width and stride frequency.

Muscle Contributions to Balance Control During Amputee and Nonamputee Stair Ascent

Dynamic balance is controlled by lower-limb muscles and is more difficult to maintain during stair ascent compared to level walking. As a result, individuals with lower-limb amputations often have difficulty ascending stairs and are more susceptible to falls. The purpose of this study was to identify the biomechanical mechanisms used by individuals with and without amputation to control dynamic balance during stair ascent. Three-dimensional muscle-actuated forward dynamics simulations of amputee and nonamputee stair ascent were developed and contributions of individual muscles, the passive prosthesis, and gravity to the time rate of change of angular momentum were determined. The prosthesis replicated the role of nonamputee plantarflexors in the sagittal plane by contributing to forward angular momentum. The prosthesis largely replicated the role of nonamputee plantarflexors in the transverse plane but resulted in a greater change of angular momentum. In the frontal plane, the prosthesis and nonamputee plantarflexors contributed oppositely during the first half of stance while during the second half of stance, the prosthesis contributed to a much smaller extent. This resulted in altered contributions from the intact leg plantarflexors, vastii and hamstrings, and the intact and residual leg hip abductors. Therefore, prosthetic devices with altered contributions to frontal-plane angular momentum could improve balance control during amputee stair ascent and minimize necessary muscle compensations. In addition, targeted training could improve the force production magnitude and timing of muscles that regulate angular momentum to improve balance control.

Biomechanics of In-Stance Balancing Responses Following Outward-Directed Perturbation to the Pelvis During Very Slow Treadmill Walking Show Complex and Well-Orchestrated Reaction of Central Nervous System

Multiple strategies may be used when counteracting loss of balance during walking. Placing the foot onto a new location is not efficient when walking speed is very low. Instead medio-lateral displacement of center-of-pressure, rotation of body segments to produce a lateral ground-reaction-force, and pronounced braking of movement in the plane of progression is used. It is, however, presently not known in what way these in-stance balancing strategies are interrelated. Twelve healthy subjects walked very slowly on an instrumented treadmill and received outward-directed pushes to the waist. We created experimental conditions where the use of stepping strategy to recover balance following an outward push was minimized by appropriately selecting the amplitude and timing of perturbation. Our experimental results showed that in the first part of the response the principal strategy used to counteract the effect of a perturbing push was a short but substantial increase in lateral ground-reaction-force. Concomitant slowing of the movement and related anterior displacement of center-of-pressure enabled lateral displacement of center-of-pressure which was, together with a short but substantial increase in vertical ground-reaction-force, instrumental in reducing the inevitable increase of whole-body angular momentum in the frontal plane. However, anterior displacement of center-of-pressure and increased vertical ground-reaction-force also induced an increase in whole-body angular momentum in the sagittal plane. In the second part of the response the lateral ground-reaction-force was decreased with respect to unperturbed walking thus allowing for a decrease of whole-body angular momentum in the frontal plane. Additionally, an increase in anterior ground-reaction-force in the second part of the response propelled the center-of-mass in the direction of movement, thus re-synchronizing it with the frontal plane component of the center-of-mass as well as decreasing whole-body angular momentum in the sagittal plane. The results of this study show that use of in-stance balancing strategies counteracts the effect a perturbing push imposed on the center-of-mass, re-synchronizes the movement of center-of-mass in sagittal and frontal planes to the values seen in unperturbed walking and maintains control of whole-body angular momentum in both frontal and sagittal planes.

Time evolution of frontal plane dynamic balance during locomotor transitions of altered anticipation and complexity

Background

Locomotor transitions between different ambulatory tasks are essential activities of daily life. During these transitions, biomechanics are affected by various factors such as anticipation, movement direction, and task complexity. These factors are thought to influence the neuromotor regulation of dynamic balance, which can be quantified using whole-body angular momentum (H). However, the specific effects of these factors on balance during transitions are not well understood. The ability to regulate dynamic balance in the presence of these contextual factors is especially important in the frontal plane, as it is usually challenging to maintain walking balance in the frontal plane for individuals with neuromuscular impairments. The purpose of this study was to apportion their effects on the time evolution of frontal plane dynamic balance during locomotor transitions of healthy, unimpaired individuals.

Methods

Five healthy young subjects performed 10 separate types of transitions with discrete combinations of factors including complexity (straight walking, cuts, combined cut/stair ascent), cut style (crossover, sidestep), and anticipation (anticipated and unanticipated). A three-way analysis of variance (ANOVA) was used to compare the maxima, minima, and average rates of change of frontal-plane H among all transitions.

Results

Before transition, within anticipated state peak value of H increased 307% in crossover style relative to sidestep style (p < 0.0001). During Transition Phase, within unanticipated state the magnitudes of average rate of change and peak value increased 70 and 46% in sidestep style compared to crossover style (p < 0.0001 and p = 0.0003). Within sidestep style, they increased in unanticipated state relative to anticipated state. Later in Correction Phase, within both anticipation states peak value of H increased 41 and 75% in cut/stairs transitions relative to cuts (p = 0.010 and p < 0.0001). For cut/stairs transitions, peak value of H increased 45% in unanticipated state compared to anticipated state (p = 0.0001).

Conclusions

These results underlined the detrimental effects of unanticipated state and task complexity on dynamic balance during walking transitions. These findings imply increased demand of neuromuscular system and functional deficits of individuals with neuromuscular disorders during these tasks. In addition, cutting style influenced frontal plane dynamic balance before transition and in response to unanticipated direction change. Collectively, these results may help identify impaired balance control of fall-prone individuals and inform interventions targeting specific destabilizing scenarios.

Modulation of soleus muscle H-reflexes and ankle muscle co-contraction with surface compliance during unipedal balancing in young and older adults

This study aimed to assess modulation of lower leg muscle reflex excitability and co-contraction during unipedal balancing on compliant surfaces in young and older adults. Twenty healthy adults (ten aged 18-30 years and ten aged 65-80 years) were recruited. Soleus muscle H-reflexes were elicited by electrical stimulation of the tibial nerve, while participants stood unipedally on a robot-controlled balance platform, simulating different levels of surface compliance. In addition, electromyographic data (EMG) of soleus (SOL), tibialis anterior (TA), and peroneus longus (PL) and full-body 3D kinematic data were collected. The mean absolute center of mass velocity was determined as a measure of balance performance. Soleus H-reflex data were analyzed in terms of the amplitude related to the M wave and the background EMG activity 100 ms prior to the stimulation. The relative duration of co-contraction was calculated for soleus and tibialis anterior, as well as for peroneus longus and tibialis anterior. Center of mass velocity was significantly higher in older adults compared to young adults ([Formula: see text] and increased with increasing surface compliance in both groups ([Formula: see text]. The soleus H-reflex gain decreased with surface compliance in young adults [Formula: see text], while co-contraction increased [Formula: see text]. Older adults did not show such modulations, but showed overall lower H-reflex gains [Formula: see text] and higher co-contraction than young adults [Formula: see text]. These results suggest an overall shift in balance control from the spinal level to supraspinal levels in older adults, which also occurred in young adults when balancing at more compliant surfaces.

The influence of lateral stabilization on walking performance and balance control in neurologically-intact and post-stroke individuals

BACKGROUND

Individuals post-stroke have an increased risk of falling, which can lead to injuries and reduced quality of life. This increased fall risk can be partially attributed to poorer balance control, which has been linked to altered post-stroke gait kinematics (e.g. an increased step width). The application of lateral stabilization to the pelvis reduces step width among neurologically-intact young and older adults, suggesting that lateral stabilization reduces the need for active frontal plane balance control. This study sought to determine if lateral stabilization is effective at improving common measures of gait performance and dynamic balance in neurologically-intact and post-stoke individuals who responded to the stabilization by reducing their step width.

METHODS

Gait performance was assessed by foot placement and propulsion symmetry while dynamic balance was assessed by peak-to-peak range of frontal plane whole body angular momentum (H_R) and pelvis and trunk sway.

FINDINGS

Controls and post-stroke Responders who reduced their step width in response to stabilization also reduced their mediolateral pelvis sway, but did not exhibit changes in gait performance. Contrary to expectations, both groups exhibited an increased H_R, possibly indicative of decreased balance control. This increase was the result of increased relative velocity between the pelvis and head, arms and trunk segment.

INTERPRETATION

These results suggest that a reduction in pelvis motion alone, as opposed to relative motion between the pelvis and upper body, may increase H_R, decrease balance control and diminish gait performance. This finding has important implications for locomotor therapies that may seek to reduce pelvis motion.

Gluteus medius dysfunction in females with chronic ankle instability is consistent at different walking speeds

BACKGROUND

Patients with chronic ankle instability often present with altered gait mechanics compared to ankle sprain copers. There is increasing evidence to suggest proximal neuromuscular alterations contribute to the injury etiology, however little is known about how these changes manifest during gait. The purpose of this study was to investigate ipsilateral gluteus maximus and medius functional activity ratios throughout treadmill walking at three speeds (preferred, 120% preferred, and 1.35 m per second) in chronic ankle instability patients compared to copers.

METHODS

28 females (14 chronic ankle instability, 14 copers) walked at the three gait speeds in randomized order. Ground reaction forces and 10-s gluteal ultrasound clips were simultaneously recorded. Clips were reduced using ground reaction forces to extract 55 measurement frames. Normalized gluteal thickness measures were used to determine functional activity ratios. 2 × 3 analyses of variance were run to assess group and speed effects on gluteal outcomes throughout walking using statistical parametric mapping. Post-hoc t-tests, mean differences, and Cohen's d effect sizes were assessed for significant findings (P ≤ .05).

FINDINGS

The chronic ankle instability group had significantly decreased gluteus medius activity throughout the entire gait cycle when compared to the coper group, independent of gait speed (P < .001, mean differences: 0.10-0.18; d: 1.00-3.17). There were no significant group or speed main effects, nor an interaction for gluteus maximus activity.

INTERPRETATION

Gluteal dysfunction throughout walking was identified in chronic ankle instability. The coper group remained within healthy reference muscle activity ranges, suggesting that proximal muscle activation alterations are associated chronic ankle impairments.

Biarticular muscles are most responsive to upper-body pitch perturbations in human standing

Balancing the upper body is pivotal for upright and efficient gait. While models have identified potentially useful characteristics of biarticular thigh muscles for postural control of the upper body, experimental evidence for their specific role is lacking. Based on theoretical findings, we hypothesised that biarticular muscle activity would increase strongly in response to upper-body perturbations. To test this hypothesis, we used a novel Angular Momentum Perturbator (AMP) that, in contrast to existing methods, perturbs the upper-body posture with only minimal effect on Centre of Mass (CoM) excursions. The impulse-like AMP torques applied to the trunk of subjects resulted in upper-body pitch deflections of up to 17° with only small CoM excursions below 2 cm. Biarticular thigh muscles (biceps femoris long head and rectus femoris) showed the strongest increase in muscular activity (mid- and long-latency reflexes, starting 100 ms after perturbation onset) of all eight measured leg muscles which highlights the importance of biarticular muscles for restoring upper-body balance. These insights could be used for improving technological aids like rehabilitation or assistive devices, and the effectiveness of physical training for fall prevention e.g. for elderly people.

Control of human gait stability through foot placement

During human walking, the centre of mass (CoM) is outside the base of support for most of the time, which poses a challenge to stabilizing the gait pattern. Nevertheless, most of us are able to walk without substantial problems. In this review, we aim to provide an integrative overview of how humans cope with an underactuated gait pattern. A central idea that emerges from the literature is that foot placement is crucial in maintaining a stable gait pattern. In this review, we explore this idea; we first describe mechanical models and concepts that have been used to predict how foot placement can be used to control gait stability. These concepts, such as for instance the extrapolated CoM concept, the foot placement estimator concept and the capture point concept, provide explicit predictions on where to place the foot relative to the body at each step, such that gait is stabilized. Next, we describe empirical findings on foot placement during human gait in unperturbed and perturbed conditions. We conclude that humans show behaviour that is largely in accordance with the aforementioned concepts, with foot placement being actively coordinated to body CoM kinematics during the preceding step. In this section, we also address the requirements for such control in terms of the sensory information and the motor strategies that can implement such control, as well as the parts of the central nervous system that may be involved. We show that visual, vestibular and proprioceptive information contribute to estimation of the state of the CoM. Foot placement is adjusted to variations in CoM state mainly by modulation of hip abductor muscle activity during the swing phase of gait, and this process appears to be under spinal and supraspinal, including cortical, control. We conclude with a description of how control of foot placement can be impaired in humans, using ageing as a primary example and with some reference to pathology, and we address alternative strategies available to stabilize gait, which include modulation of ankle moments in the stance leg and changes in body angular momentum, such as rapid trunk tilts. Finally, for future research, we believe that especially the integration of consideration of environmental constraints on foot placement with balance control deserves attention.

Muscle contributions to mediolateral and anteroposterior foot placement during walking

Foot placement is critical to balance control during walking and is primarily controlled by muscle force generation. Although gluteus medius activity has been associated with mediolateral foot placement, how other muscles contribute to foot placement is not clear. Furthermore, although dynamic walking models have suggested that anteroposterior foot placement can be passively controlled, the extent to which muscles actively contribute to anteroposterior foot placement has not been determined. The objective of this study was to identify individual muscle contributions to mediolateral and anteroposterior foot placement during walking in healthy adults. Dynamic simulations of walking were developed for six older adults and a segmental power analysis was performed to determine the individual muscle contributions to the mediolateral and anteroposterior power delivered to the foot segment. The simulations revealed the ipsilateral swing limb gluteus medius, iliopsoas, rectus femoris and hamstrings and the contralateral stance limb gluteus medius and ankle plantarflexors were primary contributors to both mediolateral and anteroposterior foot placement. Muscle contributions to foot placement were found to be highly influenced by their contributions to pelvis power, which was dominated by those muscles crossing the hip joint. Thus, impaired balance control may be improved by focusing rehabilitation interventions on optimizing the coordination of those muscles crossing the hip joint and the ankle plantarflexors.

Increasing step width reduces the requirements for subtalar joint moments and powers

The subtalar joint (STJ) contributes to the absorption and generation of mechanical energy (and power) during walking to maintain frontal plane stability. Previous observational studies have suggested that there may be a relationship between step width and STJ supination moment. This study directly tests the hypothesis that walking with a step width greater than preferred would reduce STJ moments, energy absorption, and power generation requirements, while increasing energy absorption at the hip during initial contact. Participants (n = 12, 7 females) were asked to walk on an instrumented treadmill at a constant velocity and cadence at a range of fixed step widths ranging from 0.1 to 0.4 times leg length (L). Walking at step widths greater than preferred (0.149 ± 0.04 L) reduced peak STJ moments at initial contact and propulsion which subsequently reduced the negative and positive work performed at the STJ. There was a 43% reduction in energy absorption (negative work) and approximately 30% decrease in positive work at the STJ as step width increased from 0.1 L to 0.4 L. An increase in energy absorption at the knee and hip was evident with an increase in step width during initial contact, although minimal mechanical changes were observed at the proximal joints during propulsion. These results suggest an increase in step width reduces the forces generated by muscles at the STJ across stance and is therefore likely to be beneficial in the prevention and treatment of their injuries. In terms of rehabilitation, the increase in mechanical costs occurring due to an increase in energy absorption by the hip and knee is of minimal concern.

The influence of locomotor training on dynamic balance during steady-state walking post-stroke

Slow walking speed and lack of balance control are common impairments post-stroke. While locomotor training often improves walking speed, its influence on dynamic balance is unclear. The goal of this study was to assess the influence of a locomotor training program on dynamic balance in individuals post-stroke during steady-state walking and determine if improvements in walking speed are associated with improved balance control. Kinematic and kinetic data were collected pre- and post-training from seventeen participants who completed a 12-week locomotor training program. Dynamic balance was quantified biomechanically (peak-to-peak range of frontal plane whole-body angular-momentum) and clinically (Berg-Balance-Scale and Dynamic-Gait-Index). To understand the underlying biomechanical mechanisms associated with changes in angular-momentum, foot placement and ground-reaction-forces were quantified. As a group, biomechanical assessments of dynamic balance did not reveal any improvements after locomotor training. However, improved dynamic balance post-training, observed in a sub-group of 10 participants (i.e., Responders), was associated with a narrowed paretic foot placement and higher paretic leg vertical ground-reaction-force impulse during late stance. Dynamic balance was not improved post-training in the remaining seven participants (i.e., Non-responders), who did not alter their foot placement and had an increased reliance on their nonparetic leg during weight-bearing. As a group, increased walking speed was not correlated with improved dynamic balance. However, a higher pre-training walking speed was associated with higher gains in dynamic balance post-training. These findings highlight the importance of the paretic leg weight bearing and mediolateral foot placement in improving frontal plane dynamic balance post-stroke.

Whole-body and segment angular momentum during 90-degree turns

BACKGROUND

Turning is a frequently performed, asymmetric task of daily living. The asymmetric nature makes turning challenging to perform while maintaining balance.

RESEARCH QUESTION

How do healthy individuals maintain dynamic balance, quantified as whole-body angular momentum, during a 90-degree turn compared to straight-line walking?

METHODS

The kinematics of sixteen healthy individuals were tracked during walking in a straight-line and during left and right 90-degree turns at a comfortable pace. Whole-body and segment angular momenta were calculated and the relative contributions of the legs, arms, pelvis and head/trunk to whole-body angular momentum were evaluated.

RESULTS

Average whole-body angular momentum was different during turning compared to straight-line walking in all planes of motion. The initiation of a turn required generation of whole body angular momentum in all three planes of motion, which was counteracted at the end of the turn by a generation of angular momentum in the opposite direction in the frontal and sagittal planes. Transverse plane momentum was always directed in the turn direction. All segment groups, except for the inside leg, had a greater magnitude of angular momentum during turning compared to straight-line walking. The outside leg and head/trunk segments were the largest contributors to frontal and transverse plane whole-body angular momentum.

SIGNIFICANCE

Understanding how body segments contribute to maintaining balance during a 90-degree turn can be useful for designing rehabilitation paradigms for people who have difficulty turning or impaired balance.

Uneven terrain exacerbates the deficits of a passive prosthesis in the regulation of whole body angular momentum in individuals with a unilateral transtibial amputation

BACKGROUND

Uneven ground is a frequently encountered, yet little-studied challenge for individuals with amputation. The absence of control at the prosthetic ankle to facilitate correction for surface inconsistencies, and diminished sensory input from the extremity, add unpredictability to an already complex control problem, and leave limited means to produce appropriate corrective responses in a timely manner. Whole body angular momentum, L, and its variability across several strides may provide insight into the extent to which an individual can regulate their movement in such a context. The aim of this study was to explore L in individuals with a transtibial amputation, when challenged by an uneven surface. We hypothesized that, similar to previous studies, sagittal plane L would be asymmetrical on uneven terrain, and further, that uneven terrain would evoke a greater variability in L from stride to stride in individuals with amputation in comparison to unimpaired individuals, due to a limited ability to discern and correct for changing contours beneath the prosthetic foot.

METHODS

We examined sagittal plane L in ten individuals with a unilateral transtibial amputation and age- and gender- matched control participants walking on flat (FT) and uneven (UT) treadmills. The average range of L in the first 50% of the gait cycle (L_R), the average L at foot contact (L_C) and their standard deviations (vL_R, vL_C) were computed over 60 strides on each treadmill.

RESULTS

On both surfaces we observed a higher L_R on the prosthetic side and a reduced L_C on the sound side (p < 0.001) in the amputee cohort, consistent with previous findings. UT invoked an increase in L_C (p = 0.006), but not L_R (p = 0.491). vL_R, and vL_C were higher in individuals with amputation (p < 0.001, p = 0.002), and increased in both groups on UT (p < 0.001).

CONCLUSIONS

These findings support previous assertions that individuals with amputation regulate L less effectively, and suggest that the deficits of the prosthesis are exacerbated on uneven terrain, potentially to the detriment of balance. Further, the results indicate that a greater demand may be placed on the unaffected side to control movement.

Statistical analysis of timeseries data reveals changes in 3D segmental coordination of balance in response to prosthetic ankle power on ramps

Active ankle-foot prostheses generate mechanical power during the push-off phase of gait, which can offer advantages over passive prostheses. However, these benefits manifest primarily in joint kinetics (e.g., joint work) and energetics (e.g., metabolic cost) rather than balance (whole-body angular momentum, H), and are typically constrained to push-off. The purpose of this study was to analyze differences between active and passive prostheses and non-amputees in coordination of balance throughout gait on ramps. We used Statistical Parametric Mapping (SPM) to analyze time-series contributions of body segments (arms, legs, trunk) to three-dimensional H on uphill, downhill, and level grades. The trunk and prosthetic-side leg contributions to H at toe-off when using the active prosthesis were more similar to non-amputees compared to using a passive prosthesis. However, using either a passive or active prosthesis was different compared to non-amputees in trunk contributions to sagittal-plane H during mid-stance and transverse-plane H at toe-off. The intact side of the body was unaffected by prosthesis type. In contrast to clinical balance assessments (e.g., single-leg standing, functional reach), our analysis identifies significant changes in the mechanics of segmental coordination of balance during specific portions of the gait cycle, providing valuable biofeedback for targeted gait retraining.

Increased use of stepping strategy in response to medio-lateral perturbations in the elderly relates to altered reactive tibialis anterior activity

BACKGROUND

The influence of aging on reactive control of balance during walking has been mainly investigated in the sagittal plane, whereas balance control in response to frontal plane perturbations is largely unexplored in the elderly. This is remarkable, given that walking mainly requires active control in the frontal plane. An extensive gait perturbation protocol was used to test whether reactive control of walking balance changes with aging and whether these changes are more pronounced in the frontal than in the sagittal plane.

RESEARCH QUESTION

Do alterations in reactive muscle activity cause an age-related shift in stepping strategy in response to perturbations in the frontal and sagittal planes during walking?

METHOD

A treadmill-based perturbation protocol imposed frontal and sagittal plane perturbations of different magnitudes during different phases of the gait cycle. Motion capture and electromyography measured the response to the different perturbations in a group of eighteen young and ten older adults.

RESULTS

Only for a small subset of the perturbations, reactive muscle activity and kinematic strategies differed between young and older subjects. When perturbation magnitude increased, the older adults relied more on a stepping strategy for inward directed frontal plane perturbations and for sagittal plane perturbation just before heelstrike. Tibialis anterior activity increased less in the older compared to the young subjects. Using simulations, we related tibialis anterior activity to backward and outward movement of the center of pressure in the stance foot and confirmed its contribution to the ankle strategy. We concluded that deficient tibialis anterior activity predisposes elderly to use stepping rather than lateral ankle strategies to control balance.

SIGNIFICANCE

Rehabilitation targets for fall prevention in elderly need to also focus on ankle muscle reactivity.

Dynamic Balance during Human Movement: Measurement and Control Mechanisms

Walking can be exceedingly complex to analyze due to highly nonlinear multi-body dynamics, nonlinear relationships between muscle excitations and resulting muscle forces, dynamic coupling that allows muscles to accelerate joints and segments they do not span, and redundant muscle control. Walking requires the successful execution of a number of biomechanical functions such as providing body support, forward propulsion and balance control, with specific muscle groups contributing to their execution. Thus, muscle injury or neurological impairment that affects muscle output can alter the successful execution of these functions and impair walking performance. The loss of balance control in particular can result in falls and subsequent injuries that lead to the loss of mobility and functional independence. Thus, it is important to assess the mechanisms used to control balance in clinical populations using reliable methods with the ultimate goal of improving rehabilitation outcomes. In this review, we highlight common clinical and laboratory-based measures used to assess balance control and their potential limitations, show how these measures have been used to analyze balance in several clinical populations, and consider the translation of specific laboratory-based measures from the research laboratory to the clinic.

Merged plantarflexor muscle activity is predictive of poor walking performance in post-stroke hemiparetic subjects

Stroke is the leading cause of long-term disability and individuals post-stroke often experience impaired walking ability. The plantarflexor (PF) muscles are critical to walking through their contributions to the ground reaction forces and body segment energetics. Previous studies have shown muscle activity during walking can be grouped into co-excited muscle sets, or modules. Improper co-activation, or merging of modules, is a common impairment in individuals post-stroke. The purpose of this study was to determine the influence of merged PF modules on walking performance in individuals post stroke by examining balance control, body support and propulsion, and walking symmetry. Muscle modules were identified using non-negative matrix factorization to classify subjects as having an independent or merged PF module. The merged group had decreased balance control with a significantly higher frontal plane whole-body angular momentum than both the independent and control groups, while the independent and control groups were not significantly different. The merged group also had higher paretic braking and nonparetic propulsion than both the independent and control groups. These results remained when comparisons were limited to subjects who had the same number of modules, indicating this was not a general effect due to subjects with merged PF having fewer modules. It is likely that a merged PF module is indicative of general PF dysfunction even when some activation occurs at the appropriate time. These results suggest an independent PF module is critical to walking performance, and thus obtaining an independent PF module should be a crucial aim of stroke rehabilitation.

A Coronally Clutching Ankle to Improve Amputee Balance on Coronally Uneven and Unpredictable Terrain

To improve the balance of individuals with lower limb amputation on coronally uneven terrain, a coronally clutching ankle (CCA) was developed to actively adapt through ±15 deg of free coronal foot rotation during the first ∼60 ms of initial contact. Three individuals with lower limb amputations were fit with the CCA and walked across an instrumented walkway with a middle step that was either flush, 15 deg inverted, or 15 deg everted. An opaque latex membrane was placed over the middle step, making the coronally uneven terrain unpredictable. Compared to participants' clinically prescribed prosthesis, the CCA exhibited significantly more coronal angular adaption during early stance. The CCA also improved participants' center of mass (COM) path regulation during the recovery step (reduced variation in mediolateral position) and reduced the use of the hip and stepping recovery strategies, suggesting it improved participants' balance and enabled a quicker recovery from the disturbance. However, use of the CCA did not significantly affect participants' ability to regulate their coronal angular momentum during the disturbance, suggesting that the CCA did not improve all elements of dynamic balance. Reducing the distance between the CCA's pivot axis and the base of the prosthetic foot might resolve this issue. These findings suggest that actively adapting the coronal plane angle of a prosthetic ankle can improve certain elements of balance for individuals with lower limb amputation who walk on coronally uneven and unpredictable terrain.