Joyce Fung

Postural adaptation to walking on inclined surfaces: I. Normal strategies

This study investigated the postural strategies to adapt to uphill and downhill treadmill inclination (0, 5 and 10%) during walking and standing in eight healthy subjects. Increasing the treadmill grade from 0 to 10% induced an increasingly flexed posture of the hip, knee and ankle at initial foot contact as well as a progressive forward tilt of pelvis and trunk. These postural changes were accompanied by a progressive decrease in pelvic lateral drop toward the swinging limb and a gradual increase in stride length as the uphill slope became steeper. Decreasing the treadmill grade from 0 to -10% lead to a decreasingly flexed posture of the hip at initial foot contact as well as an increase in knee flexion during weight acceptance and late stance. These changes were accompanied by a gradual decrease in stride length, a progressive backward tilt of trunk and pelvis and an increase in pelvic lateral drop toward the swinging limb as downhill slope became steeper. Changes in trunk and pelvic postural alignment in the sagittal plane might be used to facilitate power generation or absorption in adapting to slope changes during walking. During quiet standing, however, the trunk and pelvis remained aligned with respect to earths vertical at any surface inclination. These results showed that postural adaptations are task-specific and the control requirements are different between standing and walking on an inclined surface.

Faster Is Better. Implications for Speed-Intensive Gait Training After Stroke

Background and Purpose— The instantaneous adaptations to speed and load changes during overground locomotion have major implications for mobility after stroke. We examined the extent to which stroke subjects could increase their overground walking speed with respect to speed and unloading changes. Methods— Twelve subjects with a unilateral stroke were evaluated while walking overground full weight bearing (FWB) or with body weight support (BWS) at preferred or fast speed. On the basis of their preferred walking speed, subjects were classified as high (≥45 cm/s) or low functioning (<45 cm/s). Gait speed, temporal distance factors (TDFs), as well as movements and muscle activation of the lower limbs were measured and compared across the conditions. Results— FWB-Fast condition induced marked (165%) increment in gait speed in all subjects. BWS at preferred speed induced faster speeds in low- but not the high-functioning subjects, whereas combined BWS and fast walking yielded further speed increments in the high-functioning subjects. Fast walking was associated with bilateral increases in joint excursion and muscle activation, as well as improved symmetry in some TDFs. BWS favored a hip flexion strategy in early swing while decreasing limb circumduction. Conclusions— This study shows that stroke subjects can increase substantially their walking speed without deleterious effects. Fast walking induces marked speed-related improvements in body and limb kinematics and muscle activation patterns. BWS during overground walking also increases gait speed, but to a lesser extent and only in low-functioning subjects. The combination of BWS with fast speed produces the greatest increments in walking speed in all subjects.

Effects of robot-assisted therapy on stroke rehabilitation in upper limbs: Systematic review and meta-analysis of the literature

We systematically reviewed and analyzed the literature to find randomized controlled trials (RCTs) that employed robotic devices in upper-limb rehabilitation of people with stroke. Out of 574 studies, 12 matching the selection criteria were found. The Fugl-Meyer, Functional Independence Measure, Motor Power Scale, and Motor Status Scale outcome measures from the selected RCTs were pooled together, and the corresponding effect sizes were estimated. We found that when the duration/intensity of conventional therapy (CT) is matched with that of the robot-assisted therapy (RT), no difference exists between the intensive CT and RT groups in terms of motor recovery, activities of daily living, strength, and motor control. However, depending on the stage of recovery, extra sessions of RT in addition to regular CT are more beneficial than regular CT alone in motor recovery of the hemiparetic shoulder and elbow of patients with stroke; gains are similar to those that have been observed in intensive CT.

Does Neurorehabilitation Play a Role in the Recovery of Walking in Neurological Populations?a

Abstract: This review demonstrates that neurorehabilitation approaches, based on recent neuroscience findings, can enhance locomotor recovery after a spinal cord injury or stroke. Findings are presented from more than 20 clinical studies conducted by numerous research groups on the effect of locomotor training using either body weight support (BWS), functional electrical stimulation (FES), pharmacological approaches or a combination of them. Among the approaches, only BWS‐assisted locomotor training has been demonstrated to have a greater effect than conventional or locomotor training alone. However, when study results were combined and weighted for the number of subjects, the results indicated that there is a gradient of effects from small changes with the immediate application of FES or BWS to larger changes when locomotor training is combined with FES or BWS or pharmacological approaches. The findings of these studies suggest that these neurorehabilitation approaches do play a role in the recovery of walking in subjects with spinal cord injury or stroke. Several factors contribute to the potential for recovery including the site, etiology, and chronicity of the injury, as well as the type, duration, and specificity of the intervention and whether interventions are combined. Furthermore, how these neurorehabilitation approaches may take advantage of the plasticity process following neurological lesion is also discussed.

Adaptation of the walking pattern to uphill walking in normal and spinal-cord injured subjects.

Abstract Lower-limb movements and muscle-activity patterns were assessed from seven normal and seven ambulatory subjects with incomplete spinal-cord injury (SCI) during level and uphill treadmill walking (5, 10 and 15°). Increasing the treadmill grade from 0° to 15° induced an increasingly flexed posture of the hip, knee and ankle during initial contact in all normal subjects, resulting in a larger excursion throughout stance. This adaptation process actually began in mid-swing with a graded increase in hip flexion and ankle dorsiflexion as well as a gradual decrease in knee extension. In SCI subjects, a similar trend was found at the hip joint for both swing and stance phases, whereas the knee angle showed very limited changes and the ankle angle showed large variations with grade throughout the walking cycle. A distinct coordination pattern between the hip and knee was observed in normal subjects, but not in SCI subjects during level walking. The same coordination pattern was preserved in all normal subjects and in five of seven SCI subjects during uphill walking. The duration of electromyographic (EMG) activity of thigh muscles was progressively increased during uphill walking, whereas no significant changes occurred in leg muscles. In SCI subjects, EMG durations of both thigh and leg muscles, which were already active throughout stance during level walking, were not significantly affected by uphill walking. The peak amplitude of EMG activity of the vastus lateralis, medial hamstrings, soleus, medial gastrocnemius and tibialis anterior was progressively increased during uphill walking in normal subjects. In SCI subjects, the peak amplitude of EMG activity of the medial hamstrings was adapted in a similar fashion, whereas the vastus lateralis, soleus and medial gastrocnemius showed very limited adaptation during uphill walking. We conclude that SCI subjects can adapt to uphill treadmill walking within certain limits, but they use different strategies to adapt to the changing locomotor demands.

A multicenter trial of a footdrop stimulator controlled by a tilt sensor.

Objectives. To test the efficacy and acceptance of a footdrop stimulator controlled by a tilt sensor. Methods. A nonrandomized, test-retest study of 26 subjects with footdrop of more than 1 year’s duration, resulting from various central nervous system disorders, was performed in 4 centers for at least 3 months. Speed of walking in a straight line, speed around a figure of 8, and physiological cost index (PCI) were measured with and without the device. Hours/day and steps/day using the device were recorded. Results.All but 2 subjects used the tilt sensor at home, rather than a foot switch. Walking speed increased by 15% after 3 months (n = 26; P < 0.01), 32% after 6 months (n = 16; P < 0.01), and 47% after 12 months (n = 8; P < 0.05), while PCI decreased. The number of steps taken per day of use increased significantly over time, and increased speed was directly correlated with usage. Walking speed also increased with the stimulator off, but to a lesser extent, indicating a training effect. Subject feedback from a questionnaire indicated satisfaction with the stimulator. Conclusions. Both efficacy and acceptance of the stimulator were good in a population of subjects with chronic footdrop.

The role of rehabilitation in the recovery of walking in the neurological population.

Recent studies demonstrate that neurological patients show great potential for recovery in both the early and late stages following injury. Enhancement of the recovery process could be achieved with new rehabilitation approaches alone or in combination with pharmacological intervention. These new approaches have evolved from fundamental advances in both animal and human studies. To date few randomized clinical trials have addressed the efficacy or effectiveness of these new approaches. In this paper, important quantitative studies will be reviewed and discussed in relation to the important mechanisms of locomotor control and plasticity that take place following lesions of the central nervous system.

Aging and selective sensorimotor strategies in the regulation of upright balance

BackgroundThe maintenance of upright equilibrium is essentially a sensorimotor integration task. The central nervous system (CNS) has to generate appropriate and complex motor responses based on the selective and rapid integration of sensory information from multiple sources. Since each sensory system has its own coordinate framework, specific time delay and reliability, sensory conflicts may arise and represent situations in which the CNS has to recalibrate the weight attributed to each particular sensory input. The resolution of sensory conflicts may represent a particular challenge for older adults given the age-related decline in the integrity of many postural regulating systems, including musculoskeletal and sensory systems, as well as neural processing and conduction of information. The effects of aging and adaptation (by repeated exposures) on the capability of the CNS to select pertinent sensory information and resolve sensory conflicts were thus investigated with virtual reality (VR) in the present study.MethodsHealthy young and older adults maintained quiet stance while immersed in a virtual environment (VE) for 1 hour during which transient visual and/or surface perturbations were randomly presented. Visual perturbations were induced by sudden pitch or roll plane tilts of the VE viewed through a helmet-mounted display, and combined with or without surface perturbations presented in a direction that was either identical or opposite to the visual perturbations.ResultsResults showed a profound influence of aging on postural adjustments measured by electromyographic (EMG) responses and displacements of the center of pressure (COP) and bodys center of mass (COM) in the recovery of upright stance, especially in the presence of sensory conflicts. Older adults relied more on vision as compared to young adults. Aging affects the interaction of the somatosensory and visual systems on the control of equilibrium during standing and the ability of CNS to resolve sensory conflicts. However, even with a one-hour immersion in VE and exposure to sensory conflicts, it is possible for the CNS to recalibrate and adapt to the changes, while improving balance capability in older adults.ConclusionPreventive and rehabilitation programs targeting postural control in older adults should take into account the possible impairment of sensory organization or sensorimotor integration and include VE training under conditions of sensory conflicts.

Posture-movement changes following repetitive motion-induced shoulder muscle fatigue

Repetitive motion-induced fatigue not only alters local motion characteristics but also provokes global reorganization of movement. However, the three-dimensional (3D) characteristics of these reorganization patterns have never been documented in detail. The goal of this study was to assess the effects of repetitive reaching-induced arm fatigue on the whole-body, 3D biomechanical task characteristics. Healthy subjects (N=14) stood and performed a continuous reaching task (RRT) between two targets placed at shoulder height to fatigue. Whole-body kinematic (Vicon), kinetic (AMTI force platforms) and electromyographic (EMG, Noraxon) characteristics were recorded. Maximal voluntary isometric efforts (MVIE) of the shoulder and elbow were measured pre- and post-RRT. Post-RRT shoulder elevation MVIE was reduced by 4.9+/-8.3% and trapezius EMG amplitude recorded during the RRT increased by 46.9+/-49.9% from the first to last minute of the RRT, indicating that arm fatigue was effectively induced. During fatigued reaching, subjects elevated their shoulder (11.7+/-10.5 mm) and decreased their average shoulder abduction angle by 8.3+/-4.4 degrees. These changes were accompanied by a lateral shift of the bodys center of mass towards the non-reaching arm. These findings suggest a compensatory strategy to decrease the load on the fatigued shoulder musculature.

Modulation of Walking Speed by Changing Optic Flow in Persons with Stroke

The present study was undertaken to compare the modulation of walking speed in response to optic flow (OF) speed changes between persons with stroke and healthy controls. Twelve individuals with stroke and 12 healthy controls walked on a self-paced treadmill viewing a virtual corridor in a helmet-mounted display. In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017Hz, from 0 to 2 times the individuals comfortable walking speed. In experiment 2, individuals were instructed to walk through a virtual hallway of 10m at their comfortable pace (control trials). During the test trials that followed the control trials, expanding optic flows ranging from 0.25 to 1.75 of the initial comfortable speed were randomly presented. Subjects were instructed to walk the test trial distance within the same time as during the preceding control trial. Results from experiment 1 showed that gait speed was modulated out-of-phase with respect to OF speed in the healthy controls, but it varied from out-of-phase to in-phase patterns in the individuals with stroke. A negative linear relationship was observed between gait speed and OF speed in healthy and stroke individuals in experiment 2. These results indicate that individuals with stroke, although able to modulate the gait speed by changing the perception of movement through different OF speeds, present with altered modulation response patterns as compared to healthy subjects