Interactions between posture and locomotion: motor patterns in humans walking with bent posture versus erect posture

Understanding gait alterations: trunk flexion and its effects on walking neuromechanics

Evolutionary and functional adaptations of morphology and postural tone of the spine and trunk are intrinsically shaped by the field of gravity in which humans move. Gravity also significantly impacts the timing and levels of neuromuscular activation, particularly in foot-support interactions. During step-to-step transitions, the centre of mass velocity must be redirected from downwards to upwards. When walking upright, this redirection is initiated by the trailing leg, propelling the body forward and upward before foot contact of the leading leg, defined as an anticipated transition. In this study, we investigated the neuromechanical adjustments when walking with a bent posture. Twenty adults walked on an instrumented treadmill at 4 km h-1 under normal (upright) conditions and with varying degrees of anterior trunk flexion (10, 20, 30 and 40 deg). We recorded lower-limb kinematics, ground reaction forces under each foot, and the electromyography activity of five lower-limb muscles. Our findings indicate that with increasing trunk flexion, there is a lack of these anticipatory step-to-step transitions, and the leading limb performs the redirection after the ground collision. Surprisingly, attenuating distal extensor muscle activity at the end of stance is one of the main impacts of trunk flexion. Our observations may help us to understand the physiological mechanisms and biomechanical regulations underlying our tendency towards an upright posture, as well as possible motor control disturbances in some diseases associated with trunk orientation problems.

Investigation of intersegmental coordination patterns in human walking

BACKGROUND

Intersegmental coordination between thigh, shank, and foot plays a crucial role in human gait, facilitating stable and efficient human walking. Limb elevation angles during the gait cycle form a planar manifold describes the by the planar covariation law, a recognized fundamental aspect of human locomotion.

RESEARCH QUESTION

How does the walking speed, age, BMI, and height, affect the size and orientation of the intersegmental coordination manifold and covariation plane?

METHODS

This study introduces novel metrics for quantifying intersegmental coordination, including the mean radius of the manifold, rotation of the manifold about the origin, and the orientation of the plane with respect to the coordinate planes. A statistical investigation is conducted on a publicly available human walking dataset for subjects aged 19-67 years, walking at speeds between 0.18 and 2.3 m s-1 to determine correlations of the proposed quantities. We used two sample t-test and ANOVA to find statistical significance of changes in the metrics with respect to gender and walking speed, respectively. Regression analysis was used to establish relationships between the introduced metrics and walking speed.

RESULTS

High correlations are observed between walking speed and the computed metrics, highlighting the sensitivity of these metrics to gait characteristics. Conversely, negligible correlations are found for demographic parameters like age, body mass index (BMI), and height. Male and female groups exhibit no practically significant differences in any of the considered metrics. Additionally, metrics tend to increase in magnitude as walking speed increases.

SIGNIFICANCE

This study contributes numerical metrics to characterize ISC of lower limbs with respect to walking speed along with regression models to estimate these metrics and related kinematic quantities. These findings hold significance for enhancing clinical gait analysis, generating optimal walking trajectories for assistive devices, prosthetics, or rehabilitation, aiming to replicate natural gaits and improve the functionality of biomechanical devices.

Forelimb muscle activation patterns in American alligators: Insights into the evolution of limb posture and powered flight in archosaurs

The evolution of archosaurs provides an important context for understanding the mechanisms behind major functional transformations in vertebrates, such as shifts from sprawling to erect limb posture and the acquisition of powered flight. While comparative anatomy and ichnology of extinct archosaurs have offered insights into musculoskeletal and gait changes associated with locomotor transitions, reconstructing the evolution of motor control requires data from extant species. However, the scarcity of electromyography (EMG) data from the forelimb, especially of crocodylians, has hindered understanding of neuromuscular evolution in archosaurs. Here, we present EMG data for nine forelimb muscles from American alligators during terrestrial locomotion. Our aim was to investigate the modulation of motor control across different limb postures and examine variations in motor control across phylogeny and locomotor modes. Among the nine muscles examined, m. pectoralis, the largest forelimb muscle and primary shoulder adductor, exhibited significantly smaller mean EMG amplitudes for steps in which the shoulder was more adducted (i.e., upright). This suggests that using a more adducted limb posture helps to reduce forelimb muscle force and work during stance. As larger alligators use a more adducted shoulder and hip posture, the sprawling to erect postural transition that occurred in the Triassic could be either the cause or consequence of the evolution of larger body size in archosaurs. Comparisons of EMG burst phases among tetrapods revealed that a bird and turtle, which have experienced major musculoskeletal transformations, displayed distinctive burst phases in comparison to those from an alligator and lizard. These results support the notion that major shifts in body plan and locomotor modes among sauropsid lineages were associated with significant changes in muscle activation patterns.

Intersegmental coordination in human slip perturbation responses

Intersegmental coordination (ISC) of lower limbs and planar covariation law (PCL) are important phenomena observed in biomechanics of human walking and other activities. Gait perturbations tend to cause deviation from the expected ISC pattern thus violating PCL. We used a data set of seven subjects, who experienced unexpected slips, to investigate and characterize the evolution of ISC during slip recoveries and falls. We have analyzed and presented the development of ISC patterns, encompassing the step preceding the slip initiation and duration of slip until it stops. The results show that the ISC patterns during slip recovery deviate considerably from the normal walking patterns. A newly proposed Euclidian distance-based metric (EDM) was used to quantify the deviation from the normal walking ISC pattern during four slip recoveries and three falls evaluated at gait events such as slip start, foot strike, and peak height of the swing foot. The timing of gait events after slip, pattern of EDM, placement of the feet after slip and temporal patterns of each limb angle have been presented. This initial investigation provides insight into the ISC during slip recovery which highlights the human natural recovery trajectories during such perturbations. The observed patterns of the ISC trajectories during slip can be used for the design of human-inspired controllers for exoskeleton devices that can provide external assistance to human subjects during balance recovery.

The Impact of Postures and Moving Directions in Fire Evacuation in a Low-Visibility Environment

Walking speed is a significant aspect of evacuation efficiency, and this speed varies during fire emergencies due to individual physical abilities. However, in evacuations, it is not always possible to keep an upright posture, hence atypical postures, such as stoop walking or crawling, may be required for survival. In this study, a novel 3D passive vision-aided inertial system (3D PVINS) for indoor positioning was used to track the movement of 20 volunteers during an evacuation in a low visibility environment. Participants' walking speeds using trunk flexion, trunk-knee flexion, and upright postures were measured. The investigations were carried out under emergency and non-emergency scenarios in vertical and horizontal directions, respectively. Results show that different moving directions led to a roughly 43.90% speed reduction, while posture accounted for over 17%. Gender, one of the key categories in evacuation models, accounted for less than 10% of the differences in speed. The speeds of participants under emergency scenarios when compared to non-emergency scenarios was also found to increase by 53.92-60% when moving in the horizontal direction, and by about 48.28-50% when moving in the vertical direction and descending downstairs. Our results also support the social force theory of the warming-up period, as well as the effect of panic on the facilitating occupants' moving speed.

Dynamic evaluation of spine kinematics in individuals with Parkinson's disease and freezing of gait

BACKGROUND

Freezing of gait (FoG) is an episodic failure of gait exposing people with Parkinson's disease (PD) to a high risk of falling. Despite growing evidence of the interconnection between impaired trunk control and FoG, a detailed description of spinal kinematics during walking is still lacking in this population.

RESEARCH QUESTION

Do spinal alterations impact gait performance in individuals with PD and FoG?

METHODS

We analyzed kinematic data of 47 PD participants suffering (PD-FOG, N = 24) or not suffering from FoG (PD-NFOG, N = 23) and 15 healthy controls (HCO) during quiet standing and unperturbed walking. We estimated the main spinal variables (i.e., spinal length, lordosis and kyphosis angles, trunk inclination), the pelvis angles, and the shoulder-pelvis angles during gait and standing. We studied differences across conditions and groups and the relationships between postural and gait parameters using linear regression methods.

RESULTS

During standing and walking, both PD groups showed increased trunk inclination and decreased lordosis angle with respect to HCO, as well as a decreased range in variation of kyphosis angle, pelvic obliquity, and shoulder-pelvis angles. Only PD-FOG participants showed reduced range of lordosis angle and spinal length compared to HCO. PD-FOG individuals were also not able to straighten their spine during walking compared to standing. Stride length and velocity were decreased in both patient groups compared to HCO, while swing duration was reduced only in the PD-FOG group. In individuals with FoG, trunk inclination and lordosis angle showed moderate but significant positive correlations with all gait alterations.

SIGNIFICANCE

Spine alterations impacted gait performance in individuals with PD suffering from FoG. Excessive trunk inclination and poor mastering of the lordosis spinal region may create an unfavourable postural precondition for forward walking. Physical therapy should target combined spinal and stepping alterations in these individuals.

Kinematics and mechanical changes with step frequency at different running speeds

PURPOSE

Running at a given speed can be achieved by taking large steps at a low frequency or on the contrary by taking small steps at a high frequency. The consequences of a change in step frequency, at a fixed speed, affects the stiffness of the lower limb differently. In this study, we compared the running mechanics and kinematics at different imposed step frequencies (from 2 step s-1 to 3.6 step s-1) to understand the relationship between kinematic and kinetic parameters.

METHODS

Eight recreational male runners ran on a treadmill at 5 different speeds and 5 different step frequencies. The lower-limb segment motion and the ground reaction forces were recorded. Mechanical powers, general gait parameters, lower-limb movements and coordination were investigated.

RESULTS

At low step frequencies, in order to limit the magnitude of the ground reaction force, the vertical stiffness is reduced and thus runners deviate from an elastic rebound. At high step frequencies, the stiffness is increased and the elastic rebound is optimised in its ability to absorb and restore energy during the contact phase.

CONCLUSION

We studied the consequences of a change in step frequency on the bouncing mechanics of running. We showed that the lower limb stiffness and the intersegmental coordination of the lower-limb segments are affected by running step frequency rather than speed. The runner rather adapts their lower limb stiffness to match a step frequency for a given speed than the opposite.

Muscle activity during crouched walking

OBJECTIVES

Muscle activity during crouched walking has been previously studied in the context of the evolution of hominin bipedalism and human movement disorders. However, crouched walking could also be used in approach hunting where postural height (actual height of the body from the ground to the top of the head during locomotion) is the limiting factor. Here, we aim to analyze the relationship between relative postural height (%stature), kinematics, and muscle activity during crouched walking.

MATERIALS AND METHODS

Adult males (n = 19) walked with extended limbs and at three degrees of crouch while their 3D motion capture kinematics and lower limb muscle electromyography were recorded. We measured activation of tibialis anterior, soleus, gastrocnemius medialis, gastrocnemius lateralis, vastus lateralis, rectus femoris, biceps femoris, and gluteus maximus. We analyzed the effects of postural height on kinematics and muscle activation using linear mixed effects model.

RESULTS

Flexion angles, individual muscle activation (except for medial gastrocnemius), and total muscle activation were negatively related to relative postural height, that is, were greater at more crouched postures. Relative postural height had a stronger effect on the activation of the thigh and gluteal muscles compared to shank muscles.

DISCUSSION

General increase in lower limb muscle activation at lower postural heights suggests a negative relationship between relative postural height and fatigue, and may indicate a possible mechanism by which short stature could benefit the hunter in approach hunting. Greater activation of thigh and gluteal muscles relative to shank muscles may help to identify crouched walking in past human populations.

Construct validity of the Mini-BESTest in individuals with chronic pain in specialized pain care

BACKGROUND

Balance assessment scales are important clinical tests to identify balance impairments. Chronic pain (> 3 months) is associated with impaired dynamic balance; however, very few balance assessment scales are psychometrically evaluated for the population. The purpose of this study was to evaluate the construct validity and internal consistency of the Mini-BESTest for individuals with chronic pain in specialized pain care.

METHODS

In this cross-sectional study, 180 individuals with chronic pain (> 3 months) were assessed with the Mini-BESTest and included in the analyses. For construct validity, five alternative factor structures were evaluated using a confirmatory factor analysis. In addition, we tested the a priori hypotheses about convergent validity with the 10-meter walk test, and divergent validity with the Brief Pain Inventory (BPI): pain intensity, the Tampa Scale of Kinesiophobia-11 (TSK-11), and the Pain Catastrophizing Scale (PCS-SW). Internal consistency was evaluated for the model with the best fit.

RESULTS

A one-factor model with added covariance via the modification indices showed adequate fit indices. In line with our hypotheses, Mini-BESTest showed convergent validity (r_s = > 0.70) with the 10-meter walk test, and divergent validity (r_s = < 0.50) with BPI pain intensity, TSK-11, and PCS-SW. Internal consistency for the one-factor model was good (α = 0.92).

CONCLUSIONS

Our study supported the construct validity and internal consistency of the Mini-BESTest for measuring balance in individuals with chronic pain, who were referred to specialized pain care. The one-factor model showed an adequate fit. In comparison, models with subscales did not reach convergence, or showed high correlations between subscales, implying that Mini-BESTest is measuring one construct in this sample. We, therefore, propose using the total score, instead of subscale scores, for individuals with chronic pain. However, further studies are necessary to establish the reliability of the Mini-BESTest in the population.

Walking like a robot: do the ground reaction forces still intersect near one point when humans imitate a humanoid robot?

Bipedal walking while keeping the upper body upright is a complex task. One strategy to cope with this task is to direct the ground reaction forces toward a point above the centre of mass of the whole body, called virtual pivot point (VPP). This behaviour could be observed in various experimental studies for human and animal walking, but not for the humanoid robot LOLA. The question arose whether humans still show a VPP when walking like LOLA. For this purpose, ten participants imitated LOLA in speed, posture, and mass distribution (LOLA-like walking). It could be found that humans do not differ from LOLA in spatio-temporal parameters for the LOLA-like walking, in contrast to upright walking with preferred speed. Eight of the participants show a VPP in all conditions (R2 > 0.90 ± 0.09), while two participants had no VPP for LOLA-like walking (R2 < 0.52). In the latter case, the horizontal ground reaction forces are not balanced around zero in the single support phase, which is presumably the key variable for the absence of the VPP.

When running is easier than walking: effects of experience and gait on human obstacle traversal in virtual reality

Humans readily traverse obstacles irrespective of whether they walk or run, despite strong differences between these gaits. Assuming that the control of human obstacle traversal may be either gait-specific or gait-independent, the present study investigates whether previous experience in an obstacle traversal task transfers between the two gaits, and, if this was the case, whether transfer worked both ways. To this end, we conducted a within-group comparison of kinematic adjustments during human obstacle traversal in both walking and running, with distinct participant groups for the two gait sequences. Participants (n = 12/12 (f/m), avg. 25 yo) were motion captured as they traversed obstacles at walking and running speeds on a treadmill, surrounded by an immersive virtual reality (VR) environment. We find that kinematics recorded in our VR setup are consistent with that obtained in real-world experiments. Comparison of learning curves reveals that participants are able to utilize previous experience and transfer learned adjustments from one gait to another. However, this transfer is not symmetrical, with previous experience during running leading to increased success rate in walking, but not the other way round. From a range of step parameters we identified lacking toe height of the trailing leg as the main cause for this asymmetry.

Effect of Unilateral Knee Extension Restriction on the Lumbar Region during Gait

Unilateral knee extension restriction might change trunk alignment and increase mechanical load on the lumbar region during walking. We aimed to clarify lumbar region mechanical load during walking with restricted knee extension using a musculoskeletal model simulation. Seventeen healthy adult males were enrolled in this study. Participants walked 10 m at a comfortable velocity with and without restricted right knee extension of 15° and 30° using a knee brace. L4-5 joint moment, joint reaction force, and muscle forces around the lumbar region during walking were calculated for each condition. Peaks of kinetic data were compared among three gait conditions during 0%-30% and 50%-80% of the right gait cycle. Lumbar extension moment at early stance of the bilateral lower limbs was significantly increased in the 30° restricted condition (p ≤ 0.021). Muscle force of the multifidus showed peaks at stance phase of the contralateral side during walking, and the erector spinae showed force peaks at early stance of the bilateral lower limb. Muscle force of the multifidus and erector spinae increased with increasing degree of knee flexion (p ≤ 0.010), with a large effect size (η ² = 0.273-0.486). The joint force acting on L4-5 showed two peaks at early stance of the bilateral lower limbs during the walking cycle. The anterior and vertical joint force on L4-5 increased by 14.2%-36.5% and 10.0%-23.0% in walking with restricted knee extension, respectively (p ≤ 0.010), with a large effect size (η ² = 0.149-0.425). Restricted knee joint extension changed trunk alignment and increased the muscle force and the vertical and anterior joint force on the L4-5 joint during walking; this tendency became more obvious with increased restriction angle. Our results provide important information for therapists engaged in the rehabilitation of patients with knee contracture.

Relation between Step-To-Step Transition Strategies and Walking Pattern in Older Adults

In older adults, two different modes of step-to-step transition have been observed: an anticipated mode when the redirection of the centre of mass of the body (COM) begins before double stance and another when the transition begins during double stance. However, the impact of transition mode on gait kinetics and kinematics has not been investigated. Age and step-to-step-transition-related differences in intersegmental coordination and in the COM trajectory during walking were identified. Fifteen young (24.1 ± 0.7 y.o.) and thirty-six older adults (74.5 ± 5.0 y.o.) walked on a treadmill at 1.11 m s−1 and 1.67 m s−1. Lower-limb motion and ground reaction force were recorded. The COM dynamics were evaluated by measuring the pendulum-like exchange of the COM energies. While all young adults and 21 of the older adults used an anticipated transition, 15 older adults presented a non-anticipated transition. Previously documented changes of intersegmental coordination with age were accentuated in older adults with non-anticipated transition (p < 0.001). Moreover, older adults with non-anticipated transition had a smaller pendulum-like energy exchange than older adults with anticipated transition (p = 0.03). The timing of COM redirection is linked to kinematic and mechanic modification of gait and could potentially be used as a quantitative assessment of age-related decline in gait.

The effects of posture on the three-dimensional gait mechanics of human walking in comparison to bipedal chimpanzees

Humans walk with an upright posture on extended limbs during stance and with a double-peaked vertical ground reaction force. Our closest living relatives, chimpanzees, are facultative bipeds that walk with a crouched posture on flexed, abducted hind limbs and with a single-peaked vertical ground reaction force. Differences in human and bipedal chimpanzee three-dimensional kinematics have been well quantified, yet it is unclear what the independent effects of using a crouched posture are on three-dimensional gait mechanics for humans, and how they compare with chimpanzees. Understanding the relationships between posture and gait mechanics, with known differences in morphology between species, can help researchers better interpret the effects of trait evolution on bipedal walking. We quantified pelvis and lower limb three-dimensional kinematics and ground reaction forces as humans adopted a series of upright and crouched postures and compared them with data from bipedal chimpanzee walking. Human crouched posture gait mechanics were more similar to bipedal chimpanzee gait than normal human walking, especially in sagittal plane hip and knee angles. However, there were persistent differences between species, as humans walked with less transverse plane pelvis rotation, less hip abduction, and greater peak horizontal ground reaction force in late stance than chimpanzees. Our results suggest that human crouched posture walking reproduces only a small subset of the characteristics of three-dimensional kinematics and ground reaction forces of chimpanzee walking, with the remaining differences likely due in large part to the distinct musculoskeletal morphologies of humans and chimpanzees.

Assessment of the Kinematic Adaptations in Parkinson's Disease Using the Gait Profile Score: Influences of Trunk Posture, a Pilot Study

INTRODUCTION

Postural abnormalities are common in patients with Parkinson's disease (PD) and lead to gait abnormalities. Relationships between changes in the trunk posture of PD patients and gait profile score (GPS) and gait spatiotemporal parameters are poorly investigated. The aim of the current study was to investigate the relationships between trunk posture, GPS, and gait spatiotemporal parameters, in patients with PD.

MATERIALS AND METHODS

Twenty-three people with PD and nineteen age-matched healthy people participated in this study. A 3D gait kinematical analysis was applied to all participants using the Plug-In Gait Full BodyTM tool. Trunk and limb kinematics patterns and gait spatio-temporal parameters of patients with PD and the control group were compared. Additionally, correlations between trunk kinematics patterns, gait spatio-temporal parameters, and GPS of the PD group were tested.

RESULTS

Cadence, opposite foot off, step time, single support, double support, foot off, gait speed, trunk kinematics, and GPS showed significant differences between the two groups (p ≤ 0.05). Posture of the trunk during gait was not related to the spatio-temporal parameters and gait profile score in the PD group. The trunk flexor pattern influenced GPS domains, mainly of the ankle and the knee.

DISCUSSION AND CONCLUSIONS

Flexed posture of the trunk in patients with PD seems to influence both ankle and knee movement patterns during the gait. The GPS analysis provided direct and simplified kinematic information for the PD group. These results may have implications for understanding the importance of considering the positioning of the trunk during gait.

Differences in Gait Stability and Acceleration Characteristics Between Healthy Young and Older Females

Our aim was to evaluate differences in gait acceleration intensity, variability, and stability of feet and trunk between older females (OF) and young females (YF) using inertial sensors. Twenty OF (mean age 68.4, SD 4.1 years) and 18 YF (mean age 22.3, SD 1.7 years) were asked to walk straight for 100 meters at their preferred speed, while wearing inertial sensors on their heels and lower back. We calculated spatiotemporal measures, foot and trunk acceleration characteristics, their variability, and trunk stability using the local divergence exponent (LDE). Two-way ANOVA (such as the factors foot and age), Student's t-test and Mann–Whitney U test were used to compare statistical differences of measures between groups. Cohen's d effects were calculated for each variable. Foot maximum vertical (VT) acceleration and amplitude, trunk-foot VT acceleration attenuation, and their variability were significantly smaller in OF than in YF. In contrast, trunk mediolateral (ML) acceleration amplitude, maximum VT acceleration, amplitude, and their variability were significantly larger in OF than in YF. Moreover, OF showed lower stability (i.e., higher LDE values) in ML acceleration, ML, and VT angular velocity of the trunk. Even though we measured healthy OF, these participants showed lower VT foot accelerations with higher VT trunk acceleration, lower trunk-foot VT acceleration attenuation, less gait stability, and more variability of the trunk, and hence, were more likely to fall. These findings suggest that instrumented gait measurements may help for early detection of changes or impairments in gait performance, even before this can be observed by clinical eye or gait speed.

Insights Into the Mini-BESTest Scoring System: Comparison of 6 Different Structural Models

OBJECTIVE

The Mini-Balance Evaluation Systems Test (Mini-BESTest) is a balance scale common to clinical practice, but different scoring has been proposed, that is, total score and/or subsections. This study aimed to investigate Mini-BESTest validity by comparing 6 structural models and to establish the best model for discriminating fallers from nonfallers, that is, those who did or did not report at least 2 falls in the 6 months before evaluation.

METHODS

In this cross-sectional validation study, data from 709 individuals with idiopathic Parkinson disease (Hoehn and Yahr stages 1-3) were analyzed. Individuals were evaluated with the Mini-BESTest, and fall history was recorded. Construct, convergent, and discriminant validity and reliability of the 6 models were analyzed. The ability of the models to adequately identify individuals with or without a history of falls was tested with receiving operating characteristic curves.

RESULTS

Confirmatory factor analysis showed that the unidimensional models and the 4-factor solutions showed the best fit indexes. Conversely, second-order models, which allowed reporting of both total and subsections, did not converge. Most models and factors showed a low convergent validity (average variance extracted values <0.5). Correlations among the anticipatory postural adjustments factor with both the sensory orientation and the dynamic gait factors of multidimensional models were high (r ≥ 0.85). Unidimensional model reliability was good, whereas low values were found in one-half of the subsections. Finally, both unidimensional models showed a large area under the receiving operating characteristic curve (0.81).

CONCLUSION

The original unidimensional Mini-BESTest model-with a total score of 28-showed the highest validity and reliability and was best at discriminating fallers from nonfallers. Conversely, its 4 subsections should not be reported separately, because they were highly correlated and had low reliability; therefore, they are not actually capable of measuring different aspects of balance.

IMPACT

This study shows that the Mini-BESTest should be used only with the original unidimensional scoring system in people with Parkinson disease.

The effects of different frequencies of rhythmic acoustic stimulation on gait stability in healthy elderly individuals: a pilot study

The efficacy of rhythmic acoustic stimulation (RAS) to improve gait and balance in healthy elderly individuals is controversial. Our aim was to investigate, through 3D gait analysis, the effect of different types of RAS (fixed frequency and based on subject-specific cadence), using conventional gait parameters and the trunk displacement as readouts. Walking at a fixed frequency of 80 bpm, the subjects showed extended duration of gait cycle and increased gait variability while the same individuals, walking at a fixed frequency of 120 bpm, showed reduced trunk sway and gait cycle duration. With regard to the RAS at subject-specific frequencies, walking at 90% of the subject-specific average cadence did not significantly modify the gait parameters, except for the speed, which was reduced. In contrast, walking at 100% and 110% of the mean cadence caused increased stride length and a slight reduction of temporal parameters and trunk sway. In conclusion, this pilot study shows that using RAS at fixed frequencies might be an inappropriate strategy, as it is not adjusted to individual gait characteristics. On the other hand, RAS frequencies equal to or slightly higher than each subject's natural cadence seem to be beneficial for gait and stability.

The Ultimate Tool: The Body, Planning of Physical Actions, and the Role of Mental Imagery in Choosing Motor Acts

The ultimate tool, it could be said, is the brain and body. Therefore, a way to understand tool use is to study the brain's control of the body. A more manageable aim is to use the tools of cognitive science to explore the planning of physical actions. Here, I focus on two kinds of physical acts which directly or indirectly involve tool use: producing finger-press sequences, and walking and reaching for objects. The main question is how people make choices between finger-press sequences, and how people make choices between walk-and-reach sequences. Are the choices made with reference to motor imagery, in which case the longer the sequences are the longer it takes to choose between them, or are shortcuts taken which rely on distinctive features of the alternatives? The reviewed experiments favor the latter alternative. The general view of action planning emerging from this work is one in which action features are highlighted and held in memory, not just to choose between potential actions but also to control the unfolding of long actions over time. Speculations are offered about tool use.

Musculoskeletal modelling of the Nile crocodile (Crocodylus niloticus) hindlimb: Effects of limb posture on leverage during terrestrial locomotion

We developed a three-dimensional, computational biomechanical model of a juvenile Nile crocodile (Crocodylus niloticus) pelvis and hindlimb, composed of 47 pelvic limb muscles, to investigate muscle function. We tested whether crocodiles, which are known to use a variety of limb postures during movement, use limb orientations (joint angles) that optimise the moment arms (leverages) or moment-generating capacities of their muscles during different limb postures ranging from a high walk to a sprawling motion. We also describe the three-dimensional (3D) kinematics of the crocodylian hindlimb during terrestrial locomotion across an instrumented walkway and a treadmill captured via X-ray Reconstruction of Moving Morphology (biplanar fluoroscopy; 'XROMM'). We reconstructed the 3D positions and orientations of each of the hindlimb bones and used dissection data for muscle lines of action to reconstruct a focal, subject-specific 3D musculoskeletal model. Motion data for different styles of walking (a high, crouched, bended and two types of sprawling motion) were fed into the 3D model to identify whether any joints adopted near-optimal poses for leverage across each of the behaviours. We found that (1) the hip adductors and knee extensors had their largest leverages during sprawling postures and (2) more erect postures typically involved greater peak moment arms about the hip (flexion-extension), knee (flexion) and metatarsophalangeal (flexion) joints. The results did not fully support the hypothesis that optimal poses are present during different locomotory behaviours because the peak capacities were not always reached around mid-stance phase. Furthermore, we obtained few clear trends for isometric moment-generating capacities. Therefore, perhaps peak muscular leverage in Nile crocodiles is instead reached either in early/late stance or possibly during swing phase or other locomotory behaviours that were not studied here, such as non-terrestrial movement. Alternatively, our findings could reflect a trade-off between having to execute different postures, meaning that hindlimb muscle leverage is not optimised for any singular posture or behaviour. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in extant crocodiles which can form a basis for investigating muscle function in extinct archosaurs.

Spatial, But Not Temporal, Kinematics of Spontaneous Upper Extremity Movements Are Related to Gross and Fine Motor Skill Attainment in Infancy

Background: Spontaneous upper extremity movements in infancy provide insight on neuromotor development. Spatiotemporal kinematics have been used to evaluate typical development of reaching, a foundational motor skill in infancy. This study evaluates the relationship between spontaneous upper extremity movements, not elicited by a toy, and motor skill attainment. Methods: N = 12 healthy infants (2–8 months) participated in this longitudinal study (one to four sessions). Motor skills were assessed with the Bayley Scales of Infant and Toddler Development, 3rd Edition: gross motor subtest (GM) and fine motor subtest. Spontaneous upper extremity movements were collected using 3D motion capture technology. Infants were placed in supine for three to twelve 30-s trials, and their movements were recorded. Repeated measure correlation coefficients (Rmcorr) were used to evaluate relationships between variables. Results: There were significant, moderate, positive relationships between the straight distance from start to end of a movement and (a) fine motor score (Rmcorr = .55, p = .03), (b) GM score (Rmcorr = .63, p = .01), and (c) age (Rmcorr = .56, p = .02). There was a significant, moderate, negative relationship between straightness ratio and GM score (Rmcorr = −.52, p = .047). Discussion: Fine and GM skills are related to the straight distance from start to end of a movement and the straightness ratio of underlying spontaneous upper extremity movements.

The effect of increasing trunk flexion during normal walking

BACKGROUND

The head, arms and trunk segment constitute a large proportion of the body's mass. Therefore, small alterations in trunk inclination may affect lower limb joint moments and muscle activation patterns. Although previous research has investigated the effect of changing frontal plane inclination of the trunk, it is not clear how increasing trunk flexion will impact on the activation of the lower limb muscles.

RESEARCH QUESTION

What is the effect of independently manipulating trunk flexion angle on lower limb kinematics, moments and muscle function?

METHODS

Gait analysis was carried out on 20 healthy people under four trunk flexion conditions: normal walking (NW), NW-5°, NW+5° and NW+10°. For the latter three conditions, a biofeedback approach was used to tightly control trunk flexion angle. A linear mixed model was used to investigate the effect of changing trunk flexion on joint angles, moments, and knee muscle activation.

RESULTS

There were clear increases in hip and ankle moments as trunk flexion was increased, but no change in knee moments. The results also showed a linear increase in knee flexor muscle activity and a corresponding increase in co-contraction as trunk flexion increased. Interestingly, there was a dramatic change in the profile of hamstring activity. In the medial hamstrings, this change led to a 100% increase in activation during early stance as flexion was increased by 5° from NW.

SIGNIFICANCE

This is the first study to demonstrate a strong dependence of knee flexor muscle activity on trunk flexion. This is important as people with knee osteoarthritis have been observed to walk with elevated muscle activation and this has been linked to increased joint loads. It is possible that these altered muscle patterns may result from increased trunk flexion during walking.

Effects of smart phone use on lower limb joint angle and dynamic balance during gait

BACKGROUND

Cognitive tasks influence gait by reducing balancing abilities. Diverse studies to date have examined dual-tasking and gait.

OBJECTIVE

This study aimed to determine the influences of smart phone use while walking on lower limb joint angle and dynamic balancing ability.

METHODS

Thirty healthy subjects were voluntarily recruited from the university population. All subjects were required to perform the tasks under three conditions: not using a smart phone, having a conversation by phone, and playing a smart phone game. Lower limb joint angle and dynamic balance ability related to smart phone use during gait were measured. Motion analysis was used to measure lower limb joint angle changes during gait, while balance measuring equipment was used to measure the dynamic balancing ability.

RESULTS

In the stability limit test to measure the changes in dynamic balancing abilities, significant differences were found among the different smart phone use conditions.

CONCLUSIONS

Smart phone use during movements that are required for balance requires special attention, and this study provides important basic data for follow-up studies.

How does normal variability in trunk flexion affect lower limb muscle activity during walking?

A large proportion of the mass of the body is contained within the trunk segment. Therefore, small changes in the inclination of this segment have the potential to influence the direction of the ground reaction force and alter lower limb joint moments and muscle activation patterns during walking. The aim of this study was to investigate if variability in sagittal trunk inclination in healthy participants is associated with differences in lower limb biomechanics. Gait analysis data was collected on 41 healthy participants during walking. Two groups were defined based on habitual trunk flexion angle during normal walking, a forward lean group (n = 18) and a backward lean group (n = 17). Lower limb moments, muscle activation patterns and co-contraction levels were compared between the two groups using independent t-tests. The forward lean group walked with 5° more trunk flexion than the backward lean group. This difference was associated with a larger peak hip moment (effect size = 0.7) and higher activation of the lateral gastrocnemius (effect size =0.6) and the biceps femoris (effect size =0.7) muscles. The forward lean group also exhibited greater co-contraction in late stance (effect size =0.7). This is the first study to demonstrate that small differences in trunk flexion are associated with pronounced alterations in the activation of the lateral knee flexor muscles. This is important because people with knee osteoarthritis have been observed to walk with increased trunk flexion. It is possible that increased sagittal trunk inclination may be associated with elevated joint loads in people with knee osteoarthritis.

The sensorimotor effects of a lower limb proprioception training intervention in individuals with a spinal cord injury

Proprioception is critical for movement control. After a spinal cord injury (SCI), individuals not only experience paralysis but may also experience proprioceptive deficits, further confounding motor recovery. The objective of this study was to test the effects of a robotic-based proprioception training protocol on lower limb proprioceptive sense in people with incomplete SCI. A secondary objective was to assess whether the effects of training transferred to a precision stepping task in people with motor-incomplete SCI. Participants with chronic incomplete SCI and able-bodied controls underwent a 2-day proprioceptive training protocol using the Lokomat robotic exoskeleton. The training involved positioning the test leg to various positions and participants were asked to report whether they felt their heel position (end-point position) was higher or lower compared with a reference position. Feedback was provided after each trial to help participants learn strategies that could help them discern different positions of their foot. Changes in end-point position as well as knee joint position sense were assessed pre- and posttraining. We also assessed the effects of proprioception training on the performance of a precision stepping task in people with motor-incomplete SCI. Following training, there were significant improvements in end-point and knee joint position sense in both groups. The magnitude of improvement was related to pretraining (baseline) proprioceptive sense, indicating that those who initially had better lower limb position sense showed greater changes. Participants also showed improvements in performance of a precision stepping task.

NEW & NOTEWORTHY We show that it is possible to alter proprioceptive sense in people with incomplete SCI using a passive proprioception training protocol combined with feedback. Improvements in proprioceptive sense transferred from end-point to joint position sense and also to an untrained precision stepping task.

Quantifying intralimb coordination of terrestrial ungulates with Fourier coefficient affine superimposition

Many phenomena related to motor behaviour in animals are spatially and temporally periodic, making them accessible for transformation to the frequency domain via Fourier Series. Although this has been applied previously, it had not been noticed that the characteristic arrangement of Fourier coefficients in their complex-valued representation resembles landmarks in geometric morphometrics. We define a superimposition procedure in the frequency domain, which removes affine differences (mean, amplitude, phase) to reveal and compare the shape of periodic kinematic measures. This procedure is conceptually linked to dynamic similarity, which can thereby be assessed on the level of individual limb elements. We demonstrate how to make intralimb coordination accessible for large-scale, quantitative analyses. By applying this to a dataset from terrestrial ungulates, dominant patterns in forelimb coordination during walking are identified. This analysis shows that typical strides of these animals differ mostly in how much the limbs are lifted in the presence or absence of obstructive substrate features. This is shown to be independent of morphological features. Besides revealing fundamental characteristics of ungulate locomotion, we argue that the suggested method is generally suitable for the large-scale quantitative assessment of coordination and dynamics in periodic locomotor phenomena.

Is the Brief-BESTest Brief Enough? Suggested Modifications Based on Structural Validity and Internal Consistency

BACKGROUND

The Brief Balance Evaluation Systems Test (Brief-BESTest) could be a useful tool for balance assessment. Although some psychometric characteristics have been examined, others still need to be clarified.

OBJECTIVE

The objective was to assess the structural validity, convergent validity, discriminant validity, and internal consistency of the Brief-BESTest in neurological patients.

DESIGN

This was a cross-sectional study.

METHODS

Data were from 416 patients with neurological disease and related balance disorders. Patients were assessed with the 5-levels Activities-Specific Balance Confidence Scale (ABC 5-levels), Brief-BESTest, and some simple balance tests (ie, 1-leg stance, Timed "Up & Go" test, functional reach, and a fall history questionnaire). Three Brief-BESTest models were examined through confirmatory factor analysis, and the following indexes were calculated: Comparative Fit Index, Tucker-Lewis Index, and root-mean-square error of approximation. Convergent validity was assessed by calculating the correlation between Brief-BESTest and ABC 5-levels total scores. Receiver operating characteristics assessed the ability of each model to differentiate between people with falls and those without falls. Internal consistency was measured with Cronbach α and coefficient ω.

RESULTS

Confirmatory factor analysis showed model 3 (Comparative Fit Index = 0.97; Tucker-Lewis Index = 0.95; root-mean-square error of approximation = 0.05), with item 1 removed and error covariance between items 3 and 4 and between items 5 and 6, to have a significantly better structure than models 1 and 2. The correlation between Brief-BESTest and ABC 5-levels was 0.61 (Spearman ρ) for all 3 models. The area under the curve of the receiver operating characteristics showed an acceptable accuracy (0.72) in distinguishing patients with a history of falls from those without a history of falls (95% confidence interval = 0.66-0.78) for all models and was superior to the areas under the curve of other simple balance tests (1-leg stance, Timed "Up & Go" test, functional reach). Cronbach α was good for Brief-BESTest models 1 (0.92) and 3 (0.92), but ω was greater than 0.80 only for model 3.

LIMITATIONS

The sample was heterogeneous.

CONCLUSIONS

The Brief-BESTest, after some changes, shows good validity and internal consistency in patients affected by different balance disorders.

Variant and Invariant Spatiotemporal Structures in Kinematic Coordination to Regulate Speed During Walking and Running

Humans walk, run, and change their speed in accordance with circumstances. These gaits are rhythmic motions generated by multi-articulated movements, which have specific spatiotemporal patterns. The kinematic characteristics depend on the gait and speed. In this study, we focused on the kinematic coordination of locomotor behavior to clarify the underlying mechanism for the effect of speed on the spatiotemporal kinematic patterns for each gait. In particular, we used seven elevation angles for the whole-body motion and separated the measured data into different phases depending on the foot-contact condition, that is, single-stance phase, double-stance phase, and flight phase, which have different physical constraints during locomotion. We extracted the spatiotemporal kinematic coordination patterns with singular value decomposition and investigated the effect of speed on the coordination patterns. Our results showed that most of the whole-body motion could be explained by only two sets of temporal and spatial coordination patterns in each phase. Furthermore, the temporal coordination patterns were invariant for different speeds, while the spatial coordination patterns varied. These findings will improve our understanding of human adaptation mechanisms to tune locomotor behavior for changing speed.

Multiphase and Multivariable Linear Controllers That Account for the Joint Torques in Normal Human Walking

OBJECTIVE

The objective of this paper is to investigate whether a small number of sequentially composed multivariable linear controllers can be used to recover a defining relation between the joint torques, angles, and velocities hidden in the walking data of multiple human subjects.

METHODS

We solve a mixed integer programming problem that defines the optimal multivariable and multiphase relation between the torques, angles, and velocities for the hip, knee, and ankle joints.

RESULTS

Using the data of seven healthy subjects, we show that the aforementioned relation can be remarkably well represented by four sequentially composed and independently activated multivariable linear controllers; the controllers account for [Formula: see text] (mean ± sem) of the variance in the joint torques across subjects, and [Formula: see text] of the variance for a new subject. We further show that each controller is associated with one of the four phases of the gait cycle, separated by toe-off and heel-strike.

CONCLUSION

The proposed controller generalizes previously developed multiphase single variable, and single phase multivariable controllers, to a multiphase multivariable controller that better explains the walking data of multiple subjects, and better generalizes to new subjects.

SIGNIFICANCE

Our result provides strong support to extend previously developed decoupled single joint controllers to coupled multijoint multivariable controllers for the control of human assistive and augmentation devices.

Feasibility of Synergy-Based Exoskeleton Robot Control in Hemiplegia

Here, we present a study on exoskeleton robot control based on inter-limb locomotor synergies using a robot control method developed to target hemiparesis. The robot control is based on inter-limb locomotor synergies and kinesiological information from the non-paretic leg and a walking aid cane to generate motion patterns for the assisted leg. The developed synergy-based system was tested against an autonomous robot control system in five patients with hemiparesis and varying locomotor abilities. Three of the participants were able to walk using the robot. Results from these participants showed an improved spatial symmetry ratio and more consistent step length with the synergy-based method compared with that for the autonomous method, while the increase in the range of motion for the assisted joints was larger with the autonomous system. The kinematic synergy distribution of the participants walking without the robot suggests a relationship between each participant's synergy distribution and his/her ability to control the robot: participants with two independent synergies accounting for approximately 80% of the data variability were able to walk with the robot. This observation was not consistently apparent with conventional clinical measures such as the Brunnstrom stages. This paper contributes to the field of robot-assisted locomotion therapy by introducing the concept of inter-limb synergies, demonstrating performance differences between synergy-based and autonomous robot control, and investigating the range of disability in which the system is usable.

Locomotor coordination in patients with Hereditary Spastic Paraplegia

Locomotion is a complex behaviour that requires the coordination of multiple body segments and muscle groups. Here we investigated how the weakness and spasticity in individuals with Hereditary Spastic Paraplegia (HSP) affect the coordination patterns of the lower limbs. We analysed kinematics and electromyographic (EMG) activity from 12 leg muscles in 21 persons with HSP and 20 control subjects at matched walking speeds. To assess the locomotor coordination, we examined the covariation between thigh, shank and foot elevation angles by means of principal component analysis and the modular organization of EMG patterns using the non-negative matrix factorization algorithm. The characteristic features of the HSP gait consisted in changes of the elevation angles covariation, the shape of the gait loop, reduced range of motion of the distal segments and significantly lower foot lift. The EMG factorization analysis revealed a comparable structure of the motor output between HSP and control groups, but significantly wider basic temporal patterns associated with muscles innervated from the sacral spinal segments in HSP. Overall, the applied methodology highlighted the impact of the corticospinal degeneration and spasticity on the coordination of distal limb segments and basic muscle modules associated with distal spinal segments.

Intersegmental coordination patterns are differently affected in Parkinson's disease and cerebellar ataxia

The law of intersegmental coordination (Borghese et al. 1996) may be altered in pathological conditions. Here we investigated the contribution of the basal ganglia (BG) and the cerebellum to lower limb intersegmental coordination by inspecting the plane's orientation and other parameters pertinent to this law in patients with idiopathic Parkinson's disease (PD) or cerebellar ataxia (CA). We also applied a mathematical model that successfully accounts for the intersegmental law of coordination observed in control subjects (Barliya et al. 2009). In the present study, we compared the planarity index (PI), covariation plane (CVP) orientation, and CVP orientation predicted by the model in 11 PD patients, 8 CA patients, and two groups of healthy subjects matched for age, height, weight, and gender to each patient group (Ctrl_PD and Ctrl_CA). Controls were instructed to alter their gait speed to match those of their respective patient group. PD patients were examined after overnight withdrawal of anti-parkinsonian medications (PD-off-med) and then on medication (PD-on-med). PI was above 96% in all gait conditions in all groups suggesting that the law of intersegmental coordination is preserved in both BG and cerebellar pathology. However, the measured and predicted CVP orientations rotated in PD-on-med and PD-off-med compared with Ctrl_PD and in CA vs. Ctrl_CA. These rotations caused by PD and CA were in opposite directions suggesting differences in the roles of the BG and cerebellum in intersegmental coordination during human locomotion. NEW & NOTEWORTHY Kinematic and muscular synergies may have a role in overcoming motor redundancies, which may be reflected in intersegmental covariation. Basal ganglia and cerebellar networks were suggested to be involved in crafting and modulating synergies. We thus compared intersegmental coordination in Parkinson's disease and cerebellar disease patients and found opposite effects in some aspects. Further research integrating muscle activities as well as biomechanical and neural control modeling are needed to account for these findings.

A kinematic synergy for terrestrial locomotion shared by mammals and birds

Locomotion of tetrapods on land adapted to different environments and needs resulting in a variety of different gait styles. However, comparative analyses reveal common principles of limb movement control. Here, we report that a kinematic synergy involving the planar covariation of limb segment motion holds in 54 different animal species (10 birds and 44 mammals), despite large differences in body size, mass (ranging from 30 g to 4 tonnes), limb configuration, and amplitude of movements. This kinematic synergy lies at the interface between the neural command signals output by locomotor pattern generators, the mechanics of the body center of mass and the external environment, and it may represent one neuromechanical principle conserved in evolution to save mechanical energy.

Animals have evolved very different body shapes and styles of movement that are adapted to their needs in the habitats they live in. For example, mice, lions and many other animals use four limbs to walk, while humans and birds only use two limbs.

The styles animals use to walk also differ in terms of how long each foot is on the ground during a single stride, and for four-legged animals, in how long a forefoot lags behind the hindfoot on the same side of the body during the stride. Yet, there are general principles in how walking is organized that are shared between animals of vastly different shapes and sizes. Many animals save energy during walking by swinging the center of their body mass back and forth like a pendulum.

Networks of neurons are responsible for controlling how and when animals move, and these networks have similar architectures and patterns of activity in many different mammals and birds. How do signals from the nervous system regulate the position of the center of body mass while an animal walks?

Here, Catavitello et al. addressed this question by analyzing how over 50 different species of birds and mammals walked around in zoo enclosures and other semi-natural or natural environments. The species studied ranged in size from mice weighing around 30 grams to elephants weighing around 4 tonnes. The team also studied human volunteers walking on treadmills.

The experiments show that all the species studied coordinate their limbs in the same way, so that the angle to which a particular segment of a limb can bend varies together with the angles that the other limb segments bend. This coordination implies that the movement of the center of body mass is regulated and energy is saved.

Along with providing new insight into how walking evolved, these findings may aid research into new approaches to treat walking impairments in humans and other animals.

Effect of spinal kypho-orthosis to gait and forward flexion in Parkinson disease

[Purpose] The gait characteristics, such as short step, decreased arm swing and stooped posture, in Parkinson disease (PD) are well established. Pharmacological and non-pharmacological treatments have been attempted to improve the gait in patients with PD. Among the non-pharmacological approaches to improve gait, spinal orthosis can be applied for patients with spinal deformity. The purpose of our study was to investigate the effect of spinal kypho-orthosis to gait in PD by using a three-dimensional analysis. [Participants and Methods] Twenty-six patients with PD with gait disturbance with forward bend posture >15°. All participants were instructed to walk along a 6-m track and turn 180° and come back to the starting point under three-dimensional motion capture. The participants performed the test again with spinal kypho-orthosis. Gait parameters during examination is compared with and without spinal kypho-orthosis. The degree of forward flexion after kypho-orthosis in patients with PD was compared. [Results] Wearing the spinal kypho-orthosis significantly improved turning performance but did not affect locomotion. The severity of forward bend posture is mildly improved after the application of spinal kypho-orthosis. [Conclusion] Spinal kypho-orthosis has a short-term effect for gait performance, particularly during turning and erect posture. Spinal kypho-orthosis can be potentially used for management of turning deficits in PD.

Effect of postural insoles on gait pattern in individuals with hemiparesis: A randomized controlled clinical trial

INTRODUCTION

Recovering the ability to walk is an important goal of physical therapy for patients who have survived cerebrovascular accident (stroke). Orthotics can provide a reduction in plantar flexion of the ankle, leading to greater stability in the stance phase of the gait cycle. Postural insoles can be used to reorganize the tone of muscle chains, which exerts an influence on postural control through correction reflexes. The aim of the present study was to perform kinematic and spatiotemporal analyses of gait in stroke survivors with hemiparesis during postural insole usage.

MATERIAL AND METHODS

Twenty stroke victims were randomly divided into two groups: 12 in the experimental group, who used insoles with corrective elements specifically designed for equinovarus foot, and eight in the control group, who used placebo insoles with no corrective elements. Both groups were also submitted to conventional physical therapy. The subjects were analyzed immediately following insole placement and after three months of insole usage. The SMART-D 140^® system (BTS Engineering) with eight cameras sensitive to infrared light and the 32-channel SMART-D INTEGRATED WORKSTATION^® were used for the three-dimensional gait evaluation.

RESULTS

Significant improvements were found in kinematic range of movement in the ankle and knee as well as gains in ankle dorsiflexion and knee flexion in the experimental group in comparison to the control group after three months of using the insoles.

CONCLUSION

Postural insoles offer significant benefits to stroke survivors regarding the kinematics of gait, as evidenced by gains in ankle dorsiflexion and knee flexion after three months of usage in combination with conventional physical therapy.

Kinematic patterns while walking on a slope at different speeds

During walking, the elevation angles of the thigh, shank, and foot (i.e., the angle between the segment and the vertical) covary along a characteristic loop constrained on a plane. Here, we investigate how the shape of the loop and the orientation of the plane, which reflect the intersegmental coordination, change with the slope of the terrain and the speed of progression. Ten subjects walked on an inclined treadmill at different slopes (between -9° and +9°) and speeds (from 0.56 to 2.22 m/s). A principal component analysis was performed on the covariance matrix of the thigh, shank, and foot elevation angles. At each slope and speed, the variance accounted for by the two principal components was >99%, indicating that the planar covariation is maintained. The two principal components can be associated to the limb orientation (PC1*) and the limb length (PC2*). At low walking speeds, changes in the intersegmental coordination across slopes are characterized mainly by a change in the orientation of the covariation plane and in PC2* and to a lesser extent, by a change in PC1*. As speed increases, changes in the intersegmental coordination across slopes are more related to a change in PC1 *, with limited changes in the orientation of the plane and in PC 2*. Our results show that the kinematic patterns highly depend on both slope and speed. NEW & NOTEWORTHY In this paper, changes in the lower-limb intersegmental coordination during walking with slope and speed are linked to changes in the trajectory of the body center of mass. Modifications in the kinematic pattern with slope depend on speed: at slow speeds, the net vertical displacement of the body during each step is related to changes in limb length and orientation. When speed increases, the vertical displacement is mostly related to a change in limb orientation.

The kinematic recovery process of rhesus monkeys after spinal cord injury

After incomplete spinal cord injury (SCI), neural circuits may be plastically reconstructed to some degree, resulting in extensive functional locomotor recovery. The present study aimed to observe the post-SCI locomotor recovery of rhesus monkey hindlimbs and compare the recovery degrees of different hindlimb parts, thus revealing the recovery process of locomotor function. Four rhesus monkeys were chosen for thoracic hemisection injury. The hindlimb locomotor performance of these animals was recorded before surgery, as well as 6 and 12 weeks post-lesion. Via principal component analysis, the relevant parameters of the limb endpoint, pelvis, hindlimb segments, and joints were processed and analyzed. Twelve weeks after surgery, partial kinematic recovery was observed at the limb endpoint, shank, foot, and knee joints, and the locomotor performance of the ankle joint even recovered to the pre-lesion level; the elevation angle of the thigh and hip joints showed no obvious recovery. Generally, different parts of a monkey hindlimb had different spontaneous recovery processes; specifically, the closer the part was to the distal end, the more extensive was the locomotor function recovery. Therefore, we speculate that locomotor recovery may be attributed to plastic reconstruction of the motor circuits that are mainly composed of corticospinal tract. This would help to further understand the plasticity of motor circuits after spinal cord injury.

Abnormal gait pattern emerges during curved trajectories in high-functioning Parkinsonian patients walking in line at normal speed

Background

Several patients with Parkinson´s disease (PD) can walk normally along straight trajectories, and impairment in their stride length and cadence may not be easily discernible. Do obvious abnormalities occur in these high-functioning patients when more challenging trajectories are travelled, such as circular paths, which normally implicate a graded modulation in the duration of the interlimb gait cycle phases?

Methods

We compared a cohort of well-treated mildly to moderately affected PD patients to a group of age-matched healthy subjects (HS), by deliberately including HS spontaneously walking at the same speed of the patients with PD. All participants performed, in random order: linear and circular walking (clockwise and counter-clockwise) at self-selected speed. By means of pressure-sensitive insoles, we recorded walking speed, cadence, duration of single support, double support, swing phase, and stride time. Stride length-cadence relationships were built for linear and curved walking. Stride-to-stride variability of temporal gait parameters was also estimated.

Results

Walking speed, cadence or stride length were not different between PD and HS during linear walking. Speed, cadence and stride length diminished during curved walking in both groups, stride length more in PD than HS. In PD compared to HS, the stride length-cadence relationship was altered during curved walking. Duration of the double-support phase was also increased during curved walking, as was variability of the single support, swing phase and double support phase.

Conclusion

The spatio-temporal gait pattern and variability are significantly modified in well-treated, high-functioning patients with PD walking along circular trajectories, even when they exhibit no changes in speed in straight-line walking. The increased variability of the gait phases during curved walking is an identifying characteristic of PD. We discuss our findings in term of interplay between control of balance and of locomotor progression: the former is challenged by curved trajectories even in high-functioning patients, while the latter may not be critically affected.

Shock attenuation in the human lumbar spine during walking and running

During locomotion, each step generates a shock wave that travels through the body toward the head. Without mechanisms for attenuation, repeated shocks can lead to pathology. Shock attenuation (SA) in the lower limb has been well studied, but little is known about how posture affects SA in the spine. To test the hypothesis that lumbar lordosis (LL) contributes to SA, 27 adults (14 male, 13 female) walked and ran on a treadmill. Two lightweight, tri-axial accelerometers were affixed to the skin overlying T12/L1 and L5/S1. Sagittal plane accelerations were analyzed using power spectral density analysis, and lumbar SA was assessed within the impact-related frequency range. 3D kinematics quantified dynamic and resting LL. To examine the effects of intervertebral discs on spinal SA, supine MRI scans were used to measure disc morphology. The results showed no association between LL and SA during walking, but LL correlated with SA during running (P<0.01, R²=0.30), resulting in as much as 64% reduction in shock signal power among individuals with the highest LL. Patterns of lumbar spinal motion partially explain differences in SA: larger amplitudes of LL angular displacement and slower angular displacement velocity during running were associated with greater lumbar SA (P=0.008, R²=0.41). Intervertebral discs were associated with greater SA during running (P=0.02, R²=0.22) but, after controlling for disc thickness, LL remained strongly associated with SA (P=0.001, R²=0.44). These findings support the hypothesis that LL plays an important role in attenuating impact shocks transmitted through the human spine during high-impact, dynamic activities such as running.

Instrumental or Physical-Exercise Rehabilitation of Balance Improves Both Balance and Gait in Parkinson's Disease

We hypothesised that rehabilitation specifically addressing balance in Parkinson's disease patients might improve not only balance but locomotion as well. Two balance-training protocols (standing on a moving platform and traditional balance exercises) were assessed by assigning patients to two groups (Platform, n = 15, and Exercises, n = 17). The platform moved periodically in the anteroposterior, laterolateral, and oblique direction, with and without vision in different trials. Balance exercises were based on the Otago Exercise Program. Both platform and exercise sessions were administered from easy to difficult. Outcome measures were (a) balancing behaviour, assessed by both Index of Stability (IS) on platform and Mini-BESTest, and (b) gait, assessed by both baropodometry and Timed Up and Go (TUG) test. Falls Efficacy Scale-International (FES-I) and Parkinson's Disease Questionnaire (PDQ-8) were administered. Both groups exhibited better balance control, as assessed both by IS and by Mini-BESTest. Gait speed at baropodometry also improved in both groups, while TUG was less sensitive to improvement. Scores of FES-I and PDQ-8 showed a marginal improvement. A four-week treatment featuring no gait training but focused on challenging balance tasks produces considerable gait enhancement in mildly to moderately affected patients. Walking problems in PD depend on postural instability and are successfully relieved by appropriate balance rehabilitation. This trial is registered with ClinicalTrials.gov NCT03314597.

Posture alteration as a measure to accommodate uneven ground in able-bodied gait

Though the effects of imposed trunk posture on human walking have been studied, less is known about such locomotion while accommodating changes in ground level. For twelve able participants, we analyzed kinematic parameters mainly at touchdown and toe-off in walking across a 10-cm visible drop in ground level (level step, pre-perturbation step, step-down, step-up) with three postures (regular erect, ~30° and ~50° of trunk flexion from the vertical). Two-way repeated measures ANOVAs revealed step-specific effects of posture on the kinematic behavior of gait mostly at toe-off of the pre-perturbation step and the step-down as well as at touchdown of the step-up. In preparation to step-down, with increasing trunk flexion the discrepancy in hip-center of pressure distance, i.e. effective leg length, (shorter at toe-off versus touchdown), compared with level steps increased largely due to a greater knee flexion at toe-off. Participants rotated their trunk backwards during step-down (2- to 3-fold backwards rotation compared with level steps regardless of trunk posture) likely to control the angular momentum of their whole body. The more pronounced trunk backwards rotation in trunk-flexed walking contributed to the observed elevated center of mass (CoM) trajectories during the step-down which may have facilitated drop negotiation. Able-bodied individuals were found to recover almost all assessed kinematic parameters comprising the vertical position of the CoM, effective leg length and angle as well as hip, knee and ankle joint angles at the end of the step-up, suggesting an adaptive capacity and hence a robustness of human walking with respect to imposed trunk orientations. Our findings may provide clinicians with insight into a kinematic interaction between posture and locomotion in uneven ground. Moreover, a backward rotation of the trunk for negotiating step-down may be incorporated into exercise-based interventions to enhance gait stability in individuals who exhibit trunk-flexed postures during walking.

Force direction patterns promote whole body stability even in hip-flexed walking, but not upper body stability in human upright walking

Directing the ground reaction forces to a focal point above the centre of mass of the whole body promotes whole body stability in human and animal gaits similar to a physical pendulum. Here we show that this is the case in human hip-flexed walking as well. For all upper body orientations (upright, 25°, 50°, maximum), the focal point was well above the centre of mass of the whole body, suggesting its general relevance for walking. Deviations of the forces' lines of action from the focal point increased with upper body inclination from 25 to 43 mm root mean square deviation (RMSD). With respect to the upper body in upright gait, the resulting force also passed near a focal point (17 mm RMSD between the net forces' lines of action and focal point), but this point was 18 cm below its centre of mass. While this behaviour mimics an unstable inverted pendulum, it leads to resulting torques of alternating sign in accordance with periodic upper body motion and probably provides for low metabolic cost of upright gait by keeping hip torques small. Stabilization of the upper body is a consequence of other mechanisms, e.g. hip reflexes or muscle preflexes.

Human Locomotion in Hypogravity: From Basic Research to Clinical Applications

We have considerable knowledge about the mechanisms underlying compensation of Earth gravity during locomotion, a knowledge obtained from physiological, biomechanical, modeling, developmental, comparative, and paleoanthropological studies. By contrast, we know much less about locomotion and movement in general under sustained hypogravity. This lack of information poses a serious problem for human space exploration. In a near future humans will walk again on the Moon and for the first time on Mars. It would be important to predict how they will move around, since we know that locomotion and mobility in general may be jeopardized in hypogravity, especially when landing after a prolonged weightlessness of the space flight. The combination of muscle weakness, of wearing a cumbersome spacesuit, and of maladaptive patterns of locomotion in hypogravity significantly increase the risk of falls and injuries. Much of what we currently know about locomotion in hypogravity derives from the video archives of the Apollo missions on the Moon, the experiments performed with parabolic flight or with body weight support on Earth, and the theoretical models. These are the topics of our review, along with the issue of the application of simulated hypogravity in rehabilitation to help patients with deambulation problems. We consider several issues that are common to the field of space science and clinical rehabilitation: the general principles governing locomotion in hypogravity, the methods used to reduce gravity effects on locomotion, the extent to which the resulting behavior is comparable across different methods, the important non-linearities of several locomotor parameters as a function of the gravity reduction, the need to use multiple methods to obtain reliable results, and the need to tailor the methods individually based on the physiology and medical history of each person.

Effects of altered sagittal trunk orientation on kinetic pattern in able-bodied walking on uneven ground

Studies of disturbed human locomotion often focus on the dynamics of the gait when either posture, movement or surface is perturbed. Yet, the interaction effects of variation of trunk posture and ground level on kinetic behaviour of able-bodied gait have not been explored. For 12 participants we investigated the kinetic behaviour, as well as velocity and contact time, across four steps including an unperturbed step on level ground, pre-perturbation, perturbation (10-cm drop) and post-perturbation steps while walking with normal speed with four postures: regular erect, with 30°, 50° and maximal sagittal trunk flexion (70°). Two-way repeated measures ANOVAs detected significant interactions of posture×step for the second peak of the vertical ground reaction force (GRF), propulsive impulse, contact time and velocity. An increased trunk flexion was associated with a systematic decrease of the second GRF peak during all steps and with a decreased contact time and an increased velocity across steps, except for the perturbation step. Pre-adaptations were more pronounced in the approach step to the drop in regular erect gait. With increased trunk flexion, walking on uneven ground exhibited reduced changes in GRF kinetic parameters relative to upright walking. It seems that in trunk-flexed gaits the trunk is used in a compensatory way during the step-down to accommodate changes in ground level by adjusting its angle leading to lower variations in centre of mass height. Exploitation of this mechanism resembles the ability of small birds in adjusting their zig-zag-like configured legs to cope with changes in ground level.

Muscle Activation Profiles and Co-Activation of Quadriceps and Hamstring Muscles around Knee Joint in Indian Primary Osteoarthritis Knee Patients

INTRODUCTION

Osteoarthritis (OA) of knee is a common joint disease. It is associated with reduced knee joint stability due to impaired quadriceps strength, pain, and an altered joint structure. There is altered muscle activation in knee OA patients, which interferes with normal load distribution around the knee and facilitates disease progression.

AIM

Our primary aim was to determine activation patterns of the muscles i.e., quadriceps and hamstrings in knee OA patients during walking. We also studied co-activation of muscles around knee joint in primary OA knee patients including directed medial and lateral co-contractions.

MATERIALS AND METHODS

This observational study was done at Department of Physical Medicine and Rehabilitation, All India Institute of Medical Sciences, New Delhi, India. Fourty-four patients with medial compartment primary knee OA were included in study after satisfying inclusion and exclusion criteria. All the patients were assessed for mean, peak and integrated Root Mean Square (RMS), EMG values, muscle activation patterns and co-activation of muscles around knee joint by surface Electromyography (EMG) analysis of Vastus Medialis Obliques (VMO), Vastus Lateralis (VL), Semitendinosus (SMT) and Biceps Femoris (BF) muscles during gait cycle. The EMG waveform for each muscle was amplitude normalized and time normalized to 100% of gait cycle and plotted on graph. Quantitative variables were assessed for normal distribution and accordingly mean±SD or median (range), as appropriate, was computed.

RESULTS

For primary OA knee, mean age 61±5 years, mean weight 63.7±10.1 kg, mean height 153.9±7.2 cm, and mean Body Mass Index (BMI) 26.8±3.0 kg/m² was found. The muscle activity of hamstrings (SMT muscle and BF) was increased during midstance, late stance and early swing phase of gait cycle as compared to quadriceps (VMO and VL) muscle activity respectively, suggesting co-contraction of opposing muscles around knee joint.

CONCLUSION

Patients with knee OA walk with increased hamstring muscle activity (during late stance and early swing phase) and reduced quadriceps recruitment. Altered neuro-muscular control around knee interferes with normal load distribution and facilitates disease progression in knee joint.

The Neandertal vertebral column 2: The lumbar spine

Here we provide the most extensive metric and morphological analysis performed to date on the Neandertal lumbar spine. Neandertal lumbar vertebrae show differences from modern humans in both the vertebral body and in the neural arch, although not all Neandertal lumbar vertebrae differ from modern humans in the same way. Differences in the vertebral foramen are restricted to the lowermost lumbar vertebrae (L4 and L5), differences in the orientation of the upper articular facets appear in the uppermost lumbar vertebrae (probably in L1 and L2-L3), and differences in the horizontal angle of the transverse process appear in L2-L4. Neandertals, when compared to modern humans, show a smaller degree of lumbar lordosis. Based on a still limited fossil sample, early hominins (australopiths and Homo erectus) had a lumbar lordosis that was similar to but below the mean of modern humans. Here, we hypothesize that from this ancestral degree of lumbar lordosis, the Neandertal lineage decreased their lumbar lordosis and Homo sapiens slightly increased theirs. From a postural point of view, the lower degree of lordosis is related to a more vertical position of the sacrum, which is also positioned more ventrally with respect to the dorsal end of the pelvis. This results in a spino-pelvic alignment that, though different from modern humans, maintained an economic postural equilibrium. Some features, such as a lower degree of lumbar lordosis, were already present in the middle Pleistocene populations ancestral to Neandertals. However, these middle Pleistocene populations do not show the full suite of Neandertal lumbar morphologies, which probably means that the characteristic features of the Neandertal lumbar spine did not arise all at once.

Relationship between dynamic balance and spatiotemporal gait symmetry in hemiplegic patients with chronic stroke

Background

Poor dynamic balance, which is common after stroke, may affect gait function. In particular, spatiotemporal asymmetrical gait patterns may occur in hemiplegic patients after stroke.

Objective

This study aimed to assess the relationship between dynamic balance and spatiotemporal gait symmetry in patients with chronic hemiplegic stroke.

Methods

To calculate symmetry ratios for step length (spatial parameter) and swing time (temporal parameter), 41 patients with chronic stroke walked at a comfortable speed. The dynamic balance measures included limit of stability (LOS) during standing and heel-to-heel base of support (H-H BOS) during gait. Analysis of correlations between various measures was performed.

Results

The overall LOS score correlated with temporal gait symmetry (r = 0.66). The forward, backward, paretic, and non-paretic direction LOS scores were related to temporal gait symmetry (r = 0.38-0.62). The H-H BOS was correlated with temporal (r = -0.63) and spatial (r = -0.36) gait symmetries. Other dynamic balance variables were not significantly correlated with spatial gait symmetry.

Conclusion

Thus, control of dynamic balance abilities is related to the magnitude of temporal gait symmetry. This observation suggests that rehabilitation strategies that improve dynamic balance may enhance temporal gait symmetry in post-stroke patients.