The relation between kinematic synergy to stabilize the center of mass during walking and future fall risks: a 1-year longitudinal study

Accurate fall risk classification in elderly using one gait cycle data and machine learning

BACKGROUND

Falls among the elderly are a major societal problem. While observations of medium-distance walking using inertial sensors identified potential fall predictors, classifying individuals at risk based on single gait cycles remains elusive. This challenge stems from individual variability and step-to-step fluctuations, making accurate classification difficult.

METHODS

We recruited 44 participants, equally divided into high and low fall-risk groups. A smartphone secured on their second sacral spinous process recorded data during indoor walking. Features were extracted at each gait cycle from a 6-dimensional time series (tri-axial angular velocity and tri-axial acceleration) and classified using the gradient boosting decision tree algorithm.

FINDINGS

Mean accuracy across five-fold cross-validation was 0.936. "Age" was the most influential individual feature, while features related to acceleration in the gait direction held the highest total relative importance when aggregated by axis (0.5365).

INTERPRETATION

Combining acceleration, angular velocity data, and the gradient boosting decision tree algorithm enabled accurate fall risk classification in the elderly, previously challenging due to lack of discernible features. We reveal the first-ever identification of three-dimensional pelvic motion characteristics during single gait cycles in the high-risk group. This novel method, requiring only one gait cycle, is valuable for individuals with physical limitations hindering repetitive or long-distance walking or for use in spaces with limited walking areas. Additionally, utilizing readily available smartphones instead of dedicated equipment has potential to improve gait analysis accessibility.

Influence of aging on the control of the whole-body angular momentum during volitional stepping: An UCM-based analysis

Evidence suggests that whole-body angular momentum (WBAM) is a highly controlled mechanical variable for performing our daily motor activities safely and efficiently. Recent findings have revealed that, compared to young adults, older adults exhibit larger range of WBAM during various motor tasks, such as walking and stepping. However, it remains unclear whether these age-related changes are ascribed to a poorer control of WBAM with age or not. The purpose of the present study was to examine the effect of normal aging on WBAM control during stepping. Twelve young adults and 14 healthy older adults performed a series of volitional stepping at their preferred selected speed. An Uncontrolled Manifold (UCM) analysis was conducted to explore the presence of synergies among the angular momenta of the body segments (elemental variables) to control WBAM (performance variable); i.e., to stabilize or destabilize it. Results revealed the existence of a stronger synergy destabilizing the WBAM in the sagittal-plane older adults compared to young adults during stepping, while there was no difference between the two groups in the frontal and transversal planes. Although older participants also had a larger range of WBAM in the sagittal plane compared to young adults, we found no significant correlation between synergy index and the range of WBAM in the sagittal plane. We concluded that the age-related changes in WBAM during stepping are not ascribed to alterations in the ability to control this variable with aging.

Lack of visual information alters lower limb motor coordination to control center of mass trajectory during walking

Vision, as queen of the senses, plays a critical role in guiding locomotion. Little is known about the effects of vision on gait coordination in terms of variability. The uncontrolled manifold (UCM) approach offers a window to the structure of motor variability that has been difficult to obtain from the traditional correlation analysis. In this study, we used the UCM analysis to quantify how the lower limb motion is coordinated to control the center of mass (COM) while walking under different visual conditions. We also probed how synergy strength evolved along the stance phase. Ten healthy participants walked on the treadmill with and without visual information. Leg joint angle variance with respect to the whole-body COM was partitioned into good (i.e., the one that kept the COM) and bad (i.e., the one that changed the COM) variances. We observed that after vision was eliminated, both variances increased throughout the stance phase while the strength of the synergy (the normalized difference between the two variances) decreased significantly and even reduced to zero at heel contact. Thus, walking with restricted vision alters the strength of the kinematic synergy to control COM in the plane of progression. We also found that the strength of this synergy varied across different walking phases and gait events in both visual conditions. We concluded that the UCM analysis can quantify altered coordination of COM when vision is blocked and sheds insights on the role of vision in the synergistic control of locomotion.

Time profile of kinematic synergies of stroke gait

BACKGROUND

In stroke subjects, the motor skills differ between sides and among subjects with different levels of motor recovery, impacting inter-joint coordination. How these factors can affect the kinematic synergies over time during gait has not been investigated yet. This work aimed to determine the time profile of kinematic synergies of stroke patients throughout the single support phase of gait.

METHODS

Kinematic data from 17 stroke and 11 healthy individuals was recorded using a Vicon System. The Uncontrolled Manifold approach was employed to determine the distribution of components of variability and the synergy index. To analyze the time profile of kinematic synergies, we applied the statistical parametric mapping method. Comparisons were made within the stroke group (paretic and non-paretic limbs) and between groups (stroke and healthy). The stroke group was also subdivided into subgroups with worse and better motor recovery.

FINDINGS

There are significant differences in synergy index at the end of the single support phase between stroke and healthy subjects; paretic and non-paretic limbs; and paretic limb according to the motor recovery. Comparisons of mean values showed significantly larger values of synergy index for the paretic limb compared to the non-paretic and healthy.

INTERPRETATION

Despite the sensory-motor deficits and the atypical kinematic behavior, stroke patients can produce joint covariations to control the center of mass trajectory in the forward progression plane, but the modulation of the synergy is impaired, reflecting altered adjustments, especially in the paretic limb of subjects with worse levels of motor recovery.

Alterations of gait kinematics depend on the deformity type in the setting of adult spinal deformity

PURPOSE

To evaluate 3D kinematic alterations during gait in Adult Spinal Deformity (ASD) subjects with different deformity presentations.

METHODS

One hundred nineteen primary ASD (51 ± 19y, 90F), age and sex-matched to 60 controls, underwent 3D gait analysis with subsequent calculation of 3D lower limb, trunk and segmental spine kinematics as well as the gait deviation index (GDI). ASD were classified into three groups: 51 with sagittal malalignment (ASD-Sag: SVA > 50 mm, PT > 25°, and/or PI-LL > 10°), 28 with only frontal deformity (ASD-Front: Cobb > 20°) and 40 with only hyperkyphosis (ASD-HyperTK: TK > 60°). Kinematics were compared between groups.

RESULTS

ASD-Sag had a decreased pelvic mobility compared to controls with a decreased ROM of hips (38 vs. 45°) and knees (51 vs. 61°). Furthermore, ASD-Sag exhibited a decreased walking speed (0.8 vs. 1.2 m/s) and GDI (80 vs. 95, all p < 0.05) making them more prone to falls. ASD-HyperTK showed similar patterns but in a less pronounced way. ASD-Front had normal walking patterns. GDI, knee flex/extension and walking speed were significantly associated with SVA and PT (r = 0.30-0.65).

CONCLUSION

Sagittal spinal malalignment seems to be the driver of gait alterations in ASD. Patients with higher GT, SVA, PT or PI-LL tended to walk slower, with shorter steps in order to maintain stability with a limited flexibility in the pelvis, hips and knees. These changes were found to a lesser extent in ASD with only hyperkyphosis but not in those with only frontal deformity. 3D gait analysis is an objective tool to evaluate functionality in ASD patients depending on their type of spinal deformity.

LEVEL OF EVIDENCE I

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

Changes in kinematic synergy in older adults during walking: A two-year follow-up study

BACKGROUND

A well-controlled center of mass (CoM) in a coordinated segmental manner is required during gait. A synergy index that quantifies the strength of the synergistic control of the body segments that control the CoM can be evaluated using uncontrolled manifold (UCM) analysis. Several studies have compared the synergy index between older and younger adults; however, contradictory results have been found regarding age-related changes in the synergy index. Moreover, no study has investigated these changes longitudinally.

RESEARCH QUESTION

To evaluate age-related changes in the synergy index to control the CoM during gait in a longitudinal study.

METHODS

Twenty-five older adults participated at a baseline visit. The gait task at the two-year follow-up was completed by 16 older adults. Participants walked on a 6-m walkway at baseline and the two-year follow-up, and kinematic data were collected. Using UCM analysis, the synergy indices controlling CoM in the mediolateral and vertical directions were evaluated at baseline and follow-up. We also evaluated the Timed Up and Go (TUG) test and the strength of the knee extensor at both periods.

RESULTS

We found that TUG was significantly slower at follow-up; however, no difference was found in muscle strength. The synergy index in the mediolateral direction increased significantly after two years; such increases were found in individuals with decreased gait speed.

SIGNIFICANCE

This study showed that changes in gait patterns, including decreasing gait speed and increasing segmental coordination, may be important for gait with appropriate postural control relative to the environment and dynamic stability of the body in individuals with low functional mobility.

Uncontrolled manifold analysis of gait kinematic synergy during normal and narrow path walking in individuals with knee osteoarthritis compared to asymptomatic individuals

Knee osteoarthritis (KOA) is a common musculoskeletal disorder resulting in altered gait patterns. Uncontrolled manifold (UCM) analysis has been demonstrated as a useful approach for quantitative analysis of motor variability and synergies. The present study aimed to investigate the changes in the kinematic synergy, controlling the center of mass (COM) position while walking on normal and narrow paths in people with KOA compared to asymptomatic participants. In this cross-sectional study, twenty people with mild to moderate KOA and twenty asymptomatic individuals walked at their comfortable preferred speed across normal and narrow paths on a treadmill. The UCM analysis was performed separately using the lower limb segmental angles as elemental variables and the COM displacement as a performance variable during the stance phase of gait for the frontal and sagittal planes. The results revealed that KOA and asymptomatic individuals could exploit kinematic synergy to control the COM displacement regardless of walking conditions (p < 0.05). Furthermore, the variance within the UCM and synergy index were significantly higher on the narrow path than the normal walking in the mediolateral direction in the KOA group (p < 0.05). The findings of this study suggest that individuals with KOA modify their gait kinematic variability to ensure a stronger kinematic synergy when walking on a challenging narrow path.

Assessment of dynamic balance during walking in patients with adult spinal deformity

PURPOSE

To assess dynamic postural alignment in ASD during walking using a subject-specific 3D approach.

METHODS

69 ASD (51 ± 20 years, 77%F) and 62 controls (34 ± 13 years, 62%F) underwent gait analysis along with full-body biplanar Xrays and filled HRQoL questionnaires. Spinopelvic and postural parameters were computed from 3D skeletal reconstructions, including radiographic odontoid to hip axis angle (ODHA) that evaluates the head's position over the pelvis (rODHA), in addition to rSVA and rPT. The 3D bones were then registered on each gait frame to compute the dynamic ODHA (dODHA), dSVA, and dPT. Patients with high dODHA (> mean + 1SD in controls) were classified as ASD-DU (dynamically unbalanced), otherwise as ASD-DB (dynamically balanced). Between-group comparisons and relationship between parameters were investigated.

RESULTS

26 patients were classified as ASD-DU having an average dODHA of 10.4° (ASD-DB: 1.2°, controls: 1.7°), dSVA of 112 mm (ASD-DB: 57 mm, controls: 43 mm), and dPT of 21° (ASD-DB: 18°, controls: 14°; all p < 0.001). On static radiographs, ASD-DU group showed more severe sagittal malalignment than ASD-DB, with more altered HRQoL outcomes. The ASD-DU group had an overall abnormal walking compared to ASD-DB & controls (gait deviation index: 81 versus 93 & 97 resp., p < 0.001) showing a reduced flexion/extension range of motion at the hips and knees with a slower gait speed and shorter step length. Dynamic ODHA was correlated to HRQoL scores.

CONCLUSION

Dynamically unbalanced ASD had postural malalignment that persist during walking, associated with kinematic alterations in the trunk, pelvis, and lower limbs, making them more prone to falls. Dynamic-ODHA correlates better with HRQoL outcomes than dSVA and dPT.

Recent Advances in the Neural Control of Movements: Lessons for Functional Recovery

We review the current views on the control and coordination of movements following the traditions set by Nikolai Bernstein. In particular, we focus on the theory of neural control of effectors - from motor units to individual muscles, to joints, limbs, and to the whole body - with spatial referent coordinates organized into a hierarchy with multiple few-to-many mappings. Further, we discuss synergies ensuring stability of natural human movements within the uncontrolled manifold hypothesis. Synergies are organized within the neural control hierarchy based on the principle of motor abundance. Movement disorders are discussed as consequences of an inability to use the whole range of changes in referent coordinates (as in spasticity) and an inability to ensure controlled stability of salient variables as reflected in indices of multi-element synergies and their adjustments in preparation to actions (as in brain disorders, including Parkinson's disease, multiple-system atrophy, and stroke). At the end of the review, we discuss possible implications of this theoretical approach to peripheral disorders and their rehabilitations using, as an example, osteoarthritis. In particular, "joint stiffening" is viewed as a maladaptive strategy, which can compromise stability of salient variables during walking.