Gait Coordination Research Articles

Huntington’s Disease

Huntington's disease (HD) is a hereditary neurodegenerative disorder involving slow, progressive loss of functional capacities. Motor, psychiatric, and cognitive deterioration interfere with activities of independent living, gait, speech, and, ultimately, swallowing. Each child of an affected parent has a 50% chance of inheriting the abnormal gene and developing symptoms. There is no cure; for each involved descendent, this fatal condition is inescapable. In White populations, the prevalence of HD is approximately 40 to 75 per million. Lower frequencies have been found in Finland, Japan, Black Africa, and China. There are 30,000 Americans who are symptomatic; 150,000 are at risk (Moskowitz & Marder, 2001). The disease is caused by a polyglutamate expansion found on the short arm of chromosome 4. This CAG repeat causes mutation of the protein huntingtin; the altered protein attaches to normal huntingtin, interfering with its function. (CAG refers to the sequence of nucleic acids [cytosine, adenine, guanine], on chromosome 4 that has been identified as the locus of HD. In normal individuals the repeated sequence is 26 or fewer. CAG repeat sequences numbering 27-35 is not associated HD but if paternally transmitted may lead to HD in the next generation. In individuals with 36-39 repeats, some will not develop the disease; penetrance is less than 100%. Repeat sequences of 40 or more will always result in HD if the person lives long enough.) It is hypothesized that toxic accumulation of these protein bundles ultimately kills neurons. Other proposed causes of cell death are excitotoxity, oxidative stress, impaired energy metabolism, and apoptosis. In HD, neuronal death occurs most extensively within the basal ganglia, in the neostriatum. Other affected areas include the globus pallidus, thalamus, subthalamic nuclei, substantia nigra, and cerebellum. The average age of onset is between 35 and 42 years; the juvenile form occurs in 3% of all cases, with onset before 15 years (Martin & Gusella, 1986). Diagnosis can be confirmed with a gene test. Typically, the earliest stages of the illness are characterized by subtle personality changes-irritability, anxiety, and depression-as well as cognitive problems that interfere with personal self-management. The intermediate stages of the disease usually involve behavioral difficulties and significant interference with employment capacity. In addition, slurred speech, unsteady gait, and poor coordination lead to low self-esteem and social stigmatization. Nursing home placement becomes inevitable with decreasing capacity to perform the most basic activities of daily living (dressing, feeding, toileting) and/or severe emotional imbalance. The movement disorder is multifaceted and includes: chorea (jerky movements of the extremities); athetosis (writhing); and dystonia (a disorder of muscle tone manifesting as twisting, tilting, and arching of the neck, back, and feet). …

Electromyogram-Triggered Functional Electrical Stimulation-Assisted Walking After Partial Paralysis

Objective: Functional Electrical Stimulation (FES) triggered by manual switch provides brace-free ambulation to wheelchair dependent individuals with spinal cord injuries. An electromyogram (EMG)-based trigger can enhance the coordination between FES-assisted and volitional actions. This study evaluated the gait speed modulation and coordination of the actions of the EMG-triggered FES with the volitional movements during stand-to-walk transition after incomplete spinal cord injury. Methods: two incomplete spinal cord injured (iSCI) subjects (iSCI1: 24years, C7 motor & C6 sensory; iSCI2: 34years, T1 motor & C5 sensory) volunteered for this study. Four able-bodied volunteers provided the normative gait data. The Vicon WorkstationTM (Vicon Peak, USA) software acquired lower-body kinematics data using a seven camera motion capture system during stand-to-walk transition. The FES-assisted swing-phase in iSCI subjects was triggered with three command interfaces—manually triggered with a switch, triggered with EMG-based GED, triggered automatically at a user-selected rate. Results and Discussion: The Euclidean distance from origin of the perturbations of 18 joint angles and 18 joint velocities during stand-to-walk transition converged towards zero. It was found from the Mahalanobis distances between each pair of group means that the EMG-triggered FES-assisted iSCI gait was closest to the able-bodied normative gait clusters.

Effects of attention on the control of locomotion in individuals with chronic low back pain

BackgroundPeople who suffer from low back pain (LBP) exhibit an abnormal gait pattern, characterized by shorter stride length, greater step width, and an impaired thorax-pelvis coordination which may undermine functional walking. As a result, gait in LBP may require stronger cognitive regulation compared to pain free subjects thereby affecting the degree of automaticity of gait control. Conversely, because chronic pain has a strong attentional component, diverting attention away from the pain might facilitate a more efficient walking pattern.MethodsTwelve individuals with LBP and fourteen controls participated. Subjects walked on a treadmill at comfortable speed, under varying conditions of attentional load: (a) no secondary task, (b) naming the colors of squares on a screen, (c) naming the colors of color words ("color Stroop task"), and (d) naming the colors of words depicting motor activities. Markers were attached to the thorax, pelvis and feet. Motion was recorded using a three-camera SIMI system with a sample frequency of 100 Hz. To examine the effects of health status and attention on gait, mean and variability of stride parameters were calculated. The coordination between thoracic and pelvic rotations was quantified through the mean and variability of the relative phase between those oscillations.ResultsLBP sufferers had a lower walking speed, and consequently a smaller stride length and lower mean thorax-pelvis relative phase. Stride length variability was significantly lower in the LBP group but no significant effect of attention was observed. In both groups gait adaptations were found under performance of an attention demanding task, but significantly more so in individuals with LBP as indicated by an interaction effect on relative phase variability.ConclusionGait in LBP sufferers was characterized by less variable upper body movements. The diminished flexibility in trunk coordination was aggravated under the influence of an attention demanding task. This provides further evidence that individuals with LBP tighten their gait control, and this suggests a stronger cognitive regulation of gait coordination in LBP. These changes in gait coordination reduce the capability to deal with unexpected perturbations, and are therefore maladaptive.

Developing a technique to measure intra-limb coordination in gait: Applicable to children with cerebral palsy

Lower limb intra-limb coordination was investigated using sagittal plane kinematic data extracted from gait data recorded using a Vicon system (Vicon Motion Systems Ltd., Oxford, UK) of 20 normal (N) and 20 children with cerebral palsy (CP). Walking speed, maximum and minimum flexion and range of motion (ROM) were calculated. The repeatability of the data was checked by calculating the coefficient of multiple correlation. Data were also processed to determine angular velocity of hip and knee joints. A logical spreadsheet was devised to determine when both joints moved in the same direction (in-phase), in different directions (antiphase, AP) or if either joint was immobile (JS). In-phase joint motion was further subdivided into in-phase flexion (IPF) and in-phase extension (IPE), which comprises in-phase during stance phase (IPEst) and in-phase during swing phase (IPEsw). Data were processed using two threshold values for angular velocity below which the joint was considered to be immobile. The threshold values used were 0.05°/% of gait cycle and 0.025°/% of gait cycle. Children with cerebral palsy had reduced ROM and walked more slowly than normal children. There are significant differences between N and cerebral palsy coordination phases with marginally greater significance at the 0.05°/% threshold for most component parameters; the exception being in-phase flexion. It is therefore suggested that this threshold value (0.05°/%) is used for future work.

Gait Coordination After Stroke: Benefits of Acoustically Paced Treadmill Walking

Gait coordination often is compromised after stroke. The purpose of this study was to evaluate the efficacy of acoustically paced treadmill walking as a method for improving gait coordination in people after stroke. Ten people after stroke volunteered for the study and comprised the experimental group. Nine elderly people who were healthy served as a control group. Gait cycle parameters, interlimb coordination, and auditory-motor coordination were examined while participants walked on a treadmill with and without acoustic pacing. Stride frequency was adjusted to different acoustic pacing frequencies in all participants. In people after stroke, gait symmetry improved with acoustic pacing. They predominantly coordinated movements of the nonparetic limb to ipsilateral tones. The results suggest that acoustically paced treadmill walking provides an effective means for immediately modifying stride frequency and improving gait coordination in people after stroke and, therefore, may be usefully applied in physical therapist practice. Future research directions for developing guidelines for using acoustically paced treadmill walking in physical therapist practice are discussed.

A new measure for quantifying the bilateral coordination of human gait: effects of aging and Parkinson’s disease

The bilateral coordination of locomotion has been described in detail in animal studies and to some degree in man; however, the mechanisms that contribute to the bilateral coordination of gait in humans are not fully understood. The objective of the present study was to develop a measure for quantifying the bilateral coordination of gait and to evaluate the effects of aging and Parkinson's disease (PD) on this new metric. To this end, we compared the gait of healthy older adults to that of healthy young adults and patients with PD. Specifically, we defined the stride duration of one foot as a gait cycle or 360 degrees , determined the relative timing of contra-lateral heel-strikes, and defined this as the phase, varphi (ideally, varphi = 180 degrees for every step). The sum of the coefficient of variation of varphi and the mean absolute difference between varphi and 180 degrees was defined as the phase coordination index (PCI), representing variability and inaccuracy, respectively, in phase generation. PCI values were higher (poorer bilateral coordination) in patients with PD in comparison to the healthy older adults (P < 0.006). Although gait speed and stride time variability were similar in the healthy young and older adults, PCI values were significantly higher among the healthy elderly subjects compared to the young adults (P < 0.001). Regression analysis suggests that only about 40% of the variance in the values of PCI can be explained by the combination of gait asymmetry (as defined by the differences in each leg's swing times), gait speed and stride time variability, pointing to the independent nature of this new metric. This study demonstrates that bilateral coordination of gait deteriorates with aging, further deteriorates in PD, and is not strongly associated with other spatio-temporal features of gait.

Characteristics of sit-to-stand and gait coordination in patients with total hip replacement

Upright posture, standing up from a chair, and gait were analyzed in patients after one-sided total hip replacement and in healthy subjects (control). It was found that the patients predominantly loaded the unoperated leg when they stood quietly or rose from a chair. Subjects’ walking on a 10-m podograph treadmill showed that their walking speed was slower than that of healthy subjects and the swing phase on the side of hip replacement was longer than on the unoperated side. It was assumed that the unequal load on legs during walking, standing, and sit-to-stand performance in patients with total hip replacement was related to the sensory deficit of the artificial joint, leading to the overstrain of the unoperated leg and coxarthrosis in it.

Poster 104: Gains in Hip and Knee Coordination Consistency in Response to Functional Neuromuscular Stimulation

Objectives: To measure gait training response to functional neuromuscular stimulation (FNS) using intramuscular (IM) electrodes and to test validity and reliability of a gait coordination measure: hip and knee average coordination consistency (H/K ACC). Design: Randomized controlled trial (FNS-IM or no-FNS). Setting: medical center. Participants: 32 chronic stroke survivors (>12mo). Intervention: The training intervention for all subjects took place 1.5h/d, 5d/wk, for 12 weeks and included coordination exercise, overground gait training, and body weight−supported treadmill training.

Gait asymmetry in patients with Parkinson’s disease and elderly fallers: when does the bilateral coordination of gait require attention?

While it is known that certain pathologies may impact on left-right symmetry of gait, little is known about the mechanisms that contribute to gait symmetry or how high in the hierarchy of the control of gait symmetry is regulated in humans. To assess the contribution of cognitive function to gait symmetry, we measured gait asymmetry (GA) in three subject groups, patients with Parkinson's disease (PD, n = 21), idiopathic elderly fallers (n = 15), and healthy elderly controls (n = 11). All subjects walked, under two walking conditions: usual walking and dual tasking (cognitive loading) condition. For each subject, the swing time (SW) was calculated and averaged across strides for the left and right feet (SWL and SWR). GA was defined as: 100 x /ln(SWR/SWL)/. For both the PD patients and the elderly fallers GA values were significantly higher during the usual walking condition, as compared with the control group (P < 0.01). In addition, for both the PD patients and the elderly fallers, GA significantly increased when they walked and performed a dual task, compared with the usual walking condition (P < 0.003). In contrast, dual tasking did not affect the GA of the healthy controls (P = 0.518). GA was associated with gait speed and gait variability, but no correlations were found between GA and the asymmetry of the classic PD motor symptoms. Thus, the results suggest that the ability to generate a steady, rhythmic walk with a bilaterally coordinated gait does not rely heavily on mental attention and cognitive resources in healthy older adults. In contrast, however, when gait becomes impaired and less automatic, GA apparently relies on cognitive input and attention.

Circulating insulin‐like growth factor I and functional recovery from spinal cord injury under enriched housing conditions

Voluntary locomotor training as induced by enriched housing of rats stimulates recovery of locomotion after spinal cord injury (SCI). Generally it is thought that spinal neural networks of motor- and interneurons located in the ventral and intermediate laminae within the lumbar intumescence of the spinal cord, also referred to as central pattern generators (CPGs), are the 'producers of locomotion' and play a pivotal role in the amelioration of locomotor deficits after SCI. It has been suggested that locomotor training provides locomotor-specific sensory feedback into the CPGs, which stimulates remodeling of central nervous system pathways, including motor systems. Several molecules have been proposed to potentiate this process but the underlying mechanisms are not yet known. To understand these mechanisms, we studied the role of insulin-like growth factor (IGF) I in functional recovery from SCI under normal and enriched environment (EE) housing conditions. In a first experiment, we discovered that subcutaneous administration of IGF-I resulted in better locomotor recovery following SCI. In a second experiment, detailed analysis of the observed functional recovery induced by EE revealed full recovery of hindlimb coordination and stability of gait. This EE-dependent functional recovery was attenuated by alterations in the pre-synaptic bouton density within the ventral gray matter of the lumbar intumescence or CPG area. Neutralization of circulating IGF-I significantly blocked the effectiveness of EE housing on functional recovery and diminished the EE-induced alterations in pre-synaptic bouton density within the CPG area. These results support the use of IGF-I as a possible therapeutic aid in early rehabilitation after SCI.

Design and Implementation of NTU Wearable Exoskeleton as an Enhancement and Assistive Device

This article presents a wearable lower extremity exoskeleton (LEE) developed to enhance the ability of a human’s walking while carrying heavy loads. The ultimate goal of the current research work is to design and control a power assist system that integrates a human’s intellect for feedback and sensory purposes. The exoskeleton system in this work consists of an inner exoskeleton and an outer exoskeleton. The inner exoskeleton measures the movements of the wearer and provides these measurements to the outer exoskeleton, which supports the whole exoskeleton system to walk following the wearer. A special footpad, which is designed and attached to the outer exoskeleton, can measure the zero moment point (ZMP) of the human as well as that of the exoskeleton in time. Using the measured human ZMP as the reference, the exoskeleton’s ZMP is controlled by trunk compensation so that the exoskeleton can walk stably. A simulation platform has first been developed to examine the gait coordination through inner and outer exoskeletons. A commercially available software, xPC Target, together with other toolboxes from MATLAB, has then been used to provide a real-time operating system for controlling the exoskeleton. Real-time locomotion control of the exoskeleton is implemented in the developed environment. Finally, some experiments on different objects showed that the stable walking can be achieved in the real environment.

14.7 Measuring hip and knee intra-limb coordination in gait of normal children: Implications for children with cerebral palsy

The aim of the present study was to identify modes of coordination in cross-country skiing from a dynamical systems perspective. Participants (N = 8) skied on a treadmill using classical techniques with varying steepness (i.e., 0°–7°). Coordination was evaluated in terms of the relative frequency and relative phase between upper arms and thighs. Results revealed that the limb movements were systematically attracted towards low integer frequency ratios (i.e., 1:1 and 2:1) and in-phase (φ ≈ 0°) and anti-phase relationships (φ ≈ 180°). The increase in steepness produced shifts between the attractive modes of limb movements and a loss of stability was observed during transitions. These results suggest that principles of coordination between limbs in cross-country skiing are akin to those of non-linear coupled oscillators, as documented for a broad range of motor activities. Yet, differences with such classical findings are discussed reflecting the specific biomechanical constraints of cross-country skiing.

15.27 Characteristics of bilateral coordination of gait in patients with Parkinson's disease prone to freezing

15.27 Characteristics of bilateral coordination of gait in patients with Parkinson's disease prone to freezing

Rigidity and bradykinesia reduce interlimb coordination in Parkinsonian gait

Winogrodzka A, Wagenaar RC, Booij J, Wolters EC. Rigidity and bradykinesia reduce interlimb coordination in Parkinsonian gait. Objective To assess the influence of rigidity and bradykinesia and the extent of dopaminergic degeneration on interlimb coordination during walking in early, drug-naive patients with Parkinson’s disease (PD). Design The interlimb coordination was examined during a systematic manipulation of walking speed on a treadmill. The phase relations between arm and leg movements were related to the clinical measures of rigidity and bradykinesia as well as to the extent of dopaminergic degeneration. Setting Movement disorders outpatient clinic (including motion analysis laboratory) and a nuclear medicine department of a university hospital. Participants Twenty-nine early and drug-naive PD patients. Interventions Not applicable. Main outcome measures The interlimb coordination during walking was evaluated by studying the (continuous) relative phase relations between movements of arms and legs. The clinical assessment of rigidity and bradykinesia was performed by using the Unified Parkinson Disease Rating Scale. The dopaminergic degeneration was expressed as striatal 2β-carboxymethoxy-3β-(4-iodophenyl) tropane (β-CIT) single-photon emission computed tomography (SPECT) binding. Results The mean relative phase between arm and leg movements increased significantly with walking speed in all patients. Significant correlations were found between the rigidity and bradykinesia and the coordination measures ( P≤.007), as well as contralateral striatal [ 123I]β-CIT SPECT binding and coordination measures ( P<.001), in terms of asymmetry indices. Conclusions Early, drug-naive PD patients in this sample were able to adapt their coordination patterns when walking speed was systematically manipulated. However, bradykinesia and rigidity as well as the extent of degeneration of the dopaminergic system were associated with a limited adaptive ability (flexibility) in movement coordination. The combination of a drug treatment that controls bradykinesia and rigidity and a physical therapy exercise programs possibly using external cues mechanisms are required to obtain relevant effects on gait in PD patients.

Cerebellar dysfunction in neuroleptic naive schizophrenia patients: clinical, cognitive, and neuroanatomic correlates of cerebellar neurologic signs

BackgroundThere is increasing evidence that, aside from motor coordination, the cerebellum also plays an important role in cognition and psychiatric disorders. Our previous studies support the hypothesis that cerebellar dysfunction may disrupt the cortico-cerebellar-thalamic-cortical circuit and, in turn, lead to cognitive dysmetria in schizophrenia. The goal of this study was to investigate cerebellar dysfunction in schizophrenia by examining the clinical, cognitive, and neuroanatomic correlates of cerebellar neurologic signs in schizophrenia patients. MethodsWe compared the prevalence of cerebellar neurologic signs in 155 neuroleptic-naive schizophrenia patients against 155 age- and gender-matched healthy control subjects. Differences in clinical characteristics, standardized neuropsychologic performance, and magnetic resonance imaging brain volumes between patients with and without cerebellar signs were also examined. ResultsPatients had significantly higher rates of cerebellar signs than control subjects, with coordination of gait and stance being the most common abnormalities. Patients with lifetime alcohol abuse or dependence were no more likely than those without alcoholism to have cerebellar signs. Presence of cerebellar signs in patients was associated with poorer premorbid adjustment, more severe negative symptoms, poorer cognitive performance, and smaller cerebellar tissue volumes. ConclusionsThese findings lend further support for cerebellar dysfunction in schizophrenia.

Gait coordination in pregnancy: transverse pelvic and thoracic rotations and their relative phase

Objective. To examine the effects of pregnancy on the coordination of transverse pelvic and thoracic rotations during gait. Design. Gait of healthy pregnant women and nulligravidae was studied during treadmill walking at predetermined velocities ranging from 0.17 to 1.72 m/s. Background. Pelvis–thorax coordination during walking is altered in women with postpartum pregnancy-related pelvic girdle pain. This coordination has not been investigated in a healthy pregnant population. Methods. Comfortable walking velocity was established. Amplitudes of pelvic and thoracic rotations were calculated. Their coordination was characterized by relative Fourier phase and its standard deviation. Results. Comfortable walking velocity was significantly reduced. The amplitudes of pelvic and thoracic rotations were somewhat reduced, with significantly smaller intra-individual standard deviations. Also pelvis–thorax relative Fourier phase was somewhat smaller, its intra-individual standard deviation was negatively correlated with week of pregnancy, and significantly lower at velocities ⩾1.06 m/s. Conclusions. The general pattern of gait kinematics in pregnant women is very similar to that of nulligravidae. Still, it appears that pregnant women experience difficulties in realizing the more anti-phase pelvis–thorax coordination that is required at higher walking velocities. Relevance The present study shows that gait in healthy pregnancy is remarkably normal, but some differences in pelvis–thorax coordination were detected. In healthy pregnancy, anti-phase pelvis–thorax coordination appears difficult, but less so than in pregnancy-related pelvic girdle pain. Better understanding of gait in healthy pregnancy may provide insight into the gait problems of women with pregnancy-related pelvic girdle pain.

Biomechanics and muscle coordination of human walking: part II: lessons from dynamical simulations and clinical implications.

Principles of muscle coordination in gait have been based largely on analyses of body motion, ground reaction force and EMG measurements. However, data from dynamical simulations provide a cause-effect framework for analyzing these measurements; for example, Part I (Gait Posture, in press) of this two-part review described how force generation in a muscle affects the acceleration and energy flow among the segments. This Part II reviews the mechanical and coordination concepts arising from analyses of simulations of walking. Simple models have elucidated the basic multisegmented ballistic and passive mechanics of walking. Dynamical models driven by net joint moments have provided clues about coordination in healthy and pathological gait. Simulations driven by muscle excitations have highlighted the partial stability afforded by muscles with their viscoelastic-like properties and the predictability of walking performance when minimization of metabolic energy per unit distance is assumed. When combined with neural control models for exciting motoneuronal pools, simulations have shown how the integrative properties of the neuro-musculo-skeletal systems maintain a stable gait. Other analyses of walking simulations have revealed how individual muscles contribute to trunk support and progression. Finally, we discuss how biomechanical models and simulations may enhance our understanding of the mechanics and muscle function of walking in individuals with gait impairments.

Gait in patients with pregnancy-related pain in the pelvis: an emphasis on the coordination of transverse pelvic and thoracic rotations

Objective. To quantify gait impairments in women with pregnancy-related pain in the pelvis which persisted post-partum. Design. Nine patients and nine healthy subjects were studied during treadmill walking at different velocities. Background. Walking problems in patients with pregnancy-related pain in the pelvis have been known to exist for a long time. To date, no quantitative gait studies have been conducted in this population. Methods. Maximum attainable walking velocity was determined, amplitudes of pelvic and thoracic rotations were calculated, and spectral analysis was used to assess the harmonicity of these rotations. Coordination between pelvic and thoracic rotations was characterized as mean relative Fourier phase and weighted coherence. Results. Maximum attainable walking velocity was highly variable between patients, but on average significantly lower than in healthy controls. Moreover, patients had a significantly lower mean relative Fourier phase (again, highly variable) and higher weighted coherence. The other parameters did not differ significantly between groups. Conclusions. Coordination between pelvic and thoracic rotations in the transverse plane was affected in patients with pregnancy-related pain in the pelvis. Individual patients may apply different strategies during walking to cope with the underlying problems. Relevance Pregnancy-related pain in the pelvis is poorly understood. Patients with this condition are known to have problems with locomotion. The present study reveals that gait coordination is altered. Theoretically, this underlines the importance of analysing coordination in pathological movement. Clinically, better understanding the gait problems of women with pregnancy-related pain in the pelvis may contribute to more appropriate treatments.

Effect of Duration of Upper- and Lower-Extremity Rehabilitation Sessions and Walking Speed on Recovery of Interlimb Coordination in Hemiplegic Gait

The effects of different durations of rehabilitation sessions for the upper extremities (UEs) and lower extremities (LEs) on the recovery of interlimb coordination in hemiplegic gait in patients who have had a stroke were investigated. Fifty-three subjects who had strokes involving their middle cerebral arteries were assigned to rehabilitation programs with (1) an emphasis on the LEs, (2) an emphasis on the paretic UE, or (3) a condition in which the paretic arm (UE) and leg (LE) were immobilized with an inflatable pressure splint (control treatment). The 3 treatment regimens were applied for 30 minutes, 5 days a week, during the first 20 weeks after onset of stroke. All subjects also participated in a rehabilitation program 5 days a week that consisted of 15 minutes of UE exercises and 15 minutes of LE exercises in addition to a weekly 11/2-hour session of training in activities of daily living. A repeated-measures design was used. Differences among the 3 treatment regimens were evaluated in terms of comfortable and maximal walking speeds. In addition, mean continuous relative phase (CRP) between paretic arm and leg (PAL) movements and nonparetic arm and leg (NAL) movements and standard deviations of CRP of both limb pairs as a measurement of stability (variability) were evaluated. Comfortable walking speed improved in the group that received interventions involving the LEs compared with the group that received interventions involving the UEs and the group that received the control treatment. No differences among the 3 treatment conditions were found for the mean CRP of NAL and PAL as well as the standard deviation of CRP of both limb pairs. With the exception of an improved comfortable walking speed as a result of a longer duration of rehabilitation sessions, no differential effects of duration of rehabilitation sessions for the LEs and UEs on the variable we measured related to hemiplegic gait were found. Increasing walking speed, however, resulted in a larger mean CRP for both limb pairs, with increased stability and asymmetry of walking, indicating that walking speed influences interlimb coordination in hemiplegic gait.

Coupling of posture and gait: mode locking and parametric excitation.

We investigate the temporal coordination of human gait and posture and infer the nature of their coupling. Participants viewed a sinusoidally oscillating visual display which induced medial-lateral postural sway during treadmill walking, while display frequency was varied (0.075-1.025 Hz). First, postural responses exhibited the usual low-pass characteristic but with an additional resonance peak near the preferred stride frequency, although shifted downward by 0.12 Hz; this provides evidence of a coupling from gait to posture. Second, the step cycle adapted to mode lock with the visual driver and postural sway, as well as displaying instances of intermittency (slipping in and out of phase) and quasiperiodicity (phase wandering); this provides evidence of a coupling from posture to gait. We observed a spectrum of integer mode locks, including a large 1:1 trapping region about the stride frequency and superharmonic entrainment (stride frequency > driver frequency) at lower driver frequencies. A coupled-oscillator model that incorporates a novel parametric coupling from posture to the gait "stiffness" term reproduces these features of the data, including the resonance peak shift. Biological coordination patterns may thus emerge naturally as properties of a system of appropriately coupled oscillators.