Adaptation of gait termination on a slippery surface in Parkinson's disease.

Parkinson's disease (PD) causes instability and difficulty adapting to changing environmental and task demands. We examined the effects of PD on the adaptation of gait termination (GT) on a slippery surface under unexpected and cued circumstances. An unexpected slip perturbation during GT was followed by a slip perturbation during GT under two conditions: planned over multiple steps and cued one step prior to GT. Feed forward and feedback-based responses to the perturbation were compared to determine (1) how PD affects the ability to integrate adaptive feed forward and feedback-based GT strategies on a slippery surface, (2) if adaptations can be implemented when GT is required within one step, and (3) if behaviour changes with repeated exposure. Similar to the control group (n=10), the PD group (n=8) adapted and integrated feed forward and feedback-based components of GT under both stop conditions. Feed forward adaptations included a shorter, wider step, and appropriate stability margin modifications. Feedback-based adaptations included a longer, wider subsequent step. When cued to stop quickly, both groups maintained most of these adaptations: foot angle at contact increased in the first cued stop but adapted with practice. The group with PD differed in their ability to adapt GT with slower, wider steps and less stability.

Gaze fixation patterns for negotiating complex ground terrain.

We constantly encounter different ground terrain in our environment that we must safely traverse. The visual system is unique, as it is the only sensory system that can provide accurate and precise information about the environment at a distance through a series of fixations directed to salient objects and/or surfaces. However, how the nervous system utilizes visual information regarding complex ground terrain to guide safe foot placement is not known. We had individuals walk across a walkway with varying ground terrain while gaze fixations were monitored. Several findings emerged. First, gaze fixations were highly task-relevant in that they were predominantly made to areas eventually stepped on and their patterns tended to depend on the task instructions. Second, fixations were frequently directed to a transition region between different surfaces in addition to fixations directed to an actual surface. These results suggest that fixations are directed to regions that maximize the amount of information which the nervous system can integrate in order to facilitate safe foot placement. And third, spatial information of the upcoming ground terrain was sampled sequentially in small sections and continuously updated as the individual traversed the challenging ground terrain. This is suggestive of on-line control and may be beneficial to ensure one is able to adapt to stability concerns, unexpected changes in terrain, or sudden changes in the path taken.

An evaluation of sensorimotor integration during locomotion toward a target in Parkinson's disease.

Recent research suggests that basal ganglia dysfunction may result in problems integrating concurrent vision and proprioception during movement. We evaluated dopaminergic system involvement in this sensorimotor process during locomotion within a large sample of Parkinson's disease (PD) patients while "On" and "Off" their dopaminergic medications (n=25), in conditions that selectively manipulated the availability of proprioception, vision or both. The present experiment focused on two main objectives: i) to examine the relative influence of visual and proprioceptive inputs on locomotion and target accuracy in patients with PD; and ii) to examine the influence of dopamine replacement therapy on sensorimotor integration while moving toward the target. All participants walked at a self-selected pace on a GAITRite carpet in two baseline conditions (light and dark), as well as four experimental darkness conditions: a) to a remembered target (i.e. proprioception only), b) to a remembered target with light on chest for body position awareness (proprioception plus), c) with vision of a lit target, also with light on chest (vision and proprioception), d) pushed in wheelchair to remembered target (no proprioception or vision). Final position was measured by 2-D radial error, and revealed a group by condition interaction, suggesting that PD patients "Off" their medications move to targets with less accuracy, but approach the accuracy of healthy participants when in the "On" state. Both PD and healthy improved their accuracy with availability of concurrent vision and proprioception (condition c). Interestingly, our results demonstrate that PD "Off" performed the task with greater difficulty than when "On" medication, but only when proprioception was the sole source of feedback. Since PD, whether medicated or unmedicated were even more affected when proprioception was removed (wheelchair), a memory-related explanation can be ruled out. Our results suggest that the basal ganglia are not specifically involved in visuoproprioceptive integration; however, assimilation of proprioceptive feedback to guide an ongoing movement may be a critical function of the basal ganglia.

Control of dynamic stability during gait termination on a slippery surface.

There are three common ways by which to successfully terminate gait: decreased acceleration of whole-body center of mass (COM) through a flexor synergy in the trail leg, increased deceleration of whole-body COM through an extensor synergy in the front limb, and an energy/momentum transfer to dissipate any remaining momentum if the first two strategies are unsuccessful. Healthy individuals were asked to stop on a slippery surface while we examined their unexpected response to the slippery surface. Kinetic data from the forceplates revealed lower braking forces in the slip trials compared with normal gait-termination trials. Subjects were unable to control their center of pressure (COP) to manipulate the COM as revealed by increased deviations and maximum absolute ranges of COP movement. Subject COM deviated farther in both horizontal planes and lowered further during the slip compared with normal gait-termination trials. Arm movements were effective in dissipating forward COM movement. In addition, there likely was a transfer of forward to lateral momentum to stop forward progression. All recorded muscle activity in the lower limbs and back increased during the slip to provide support to the lower limbs and correct upright balance. The trailing limb shortened its final step to provide support to the lowering COM. The balance-correction response seen here resembles previous reactions to perturbations during locomotion suggesting there is a generalized strategy employed by the nervous system to correct for disturbances and maintain balance.

Tuned vibration absorber for suppression of rest tremor in Parkinson's disease.

A simple approach for the suppression of the tremor associated with Parkinson's disease is presented. The proposed system is a tuned vibration absorber (TVA), which has been very effective in the suppression of vibrations in an experimental model of the human arm with two degrees of freedom. Theoretical and numerical methods were used to study the behaviour of the arm model and to develop an effective tremor reduction approach. Based on these studies, a vibration absorber was designed, tested numerically and fabricated for experimental testing. Experimental investigations indicated that optimum control performance was related to the position of the controller and the excitation frequency. With a distance of 160 mm from the end of forearm, the TVA was found to have the best performance, and, for different tremor frequencies, the vibration of the experimental model was reduced by more than 80%.

"Look where you're going!": gaze behaviour associated with maintaining and changing the direction of locomotion.

In order to fully understand how vision is used to guide locomotion it is necessary to know what people look at as they move through the environment. This study provides information, hitherto lacking, regarding gaze behaviour associated with both maintaining and changing the direction of locomotion: activities that are essential for efficient navigation through our cluttered environment. Participants' spatiotemporal gaze patterns were recorded whilst they performed a task requiring that they either maintained a straight walking trajectory or changed their direction of walking by 30 degrees or 60 degrees, left or right, at the midpoint of a 9-m path. Participants were either visually cued to turn when they stepped on a trigger mat placed one step before the mid-point of the walkway (cued trials) or given verbal instruction about the required route prior to the start of each trial (advance knowledge trials). Our clear finding was that for the large majority of the time participants' gaze was aligned with environmental features lying in their current plane of progression both prior to and following the onset of the transition stride during which the direction change was implemented. This gaze behaviour was observed both during cued trials (78% of total fixation time prior to the transition stride onset and 89% following the transition stride onset) and advance knowledge trials (67% prior to transition stride onset, 92% following transition stride onset). When not aligned with the plane of progression, gaze was normally fixated on environmental features related to either known or potential future routes. Prior to changing the direction of walking, individuals invariably made saccadic eye movements in order to align gaze with the end-point of the required travel path. This gaze realignment was invariably accompanied by head reorientation, which was initiated, on average, at the same time as the saccade. On average, participants fixated gaze on their goal (represented by the cue light at the travel path end-point) until after head realignment with the new path was achieved. Additionally, the head was consistently aligned with participants' current walking direction prior to and following the transition stride even on the minority of occasions when they were looking elsewhere. These findings challenge the ecological validity of existing theories of how visual information is used to determine heading direction and are consistent with the proposal that aligning the head with the desired travel direction through coordinated eye and head movements provides the CNS with an allocentric frame of reference that is used to control the movement of the body in space.

Effect of stroke on step characteristics of obstacle crossing.

OBJECTIVE: To compare spatial and temporal measures during lead limb obstacle crossing between subjects with stroke and healthy subjects. DESIGN: Experimental, observational, with matched controls. SETTING: Geriatric rehabilitation unit in a tertiary referral hospital. PARTICIPANTS: Distance data were available for 19 subjects with stroke and 19 able-bodied subjects. Temporal data were available for 16 subjects with stroke and 16 able-bodied subjects. Subjects with stroke were inpatients and had to be able to walk 10 meters without assistance or gait aid. INTERVENTION: Subjects were required to step over high and wide obstacles, ranging from 1 to 8cm, and trials were videotaped. MAIN OUTCOME MEASURES: Toe clearance, preobstacle distance, postobstacle distance, step length, proportion of step length preobstacle, step time, preobstacle step time, postobstacle step time, and proportion of step time preobstacle were measured. RESULTS: Mann-Whitney U tests were performed to determine differences between the 2 groups. Subjects with stroke had significantly higher toe clearance, smaller postobstacle distances, and greater step times than healthy subjects. Subjects with stroke did not demonstrate a significant reduction in preobstacle distance. CONCLUSION: By modifying their lead limb trajectory during obstacle crossing, persons with stroke reduce the risk of a trip due to toe contact, but the modification may expose them to other safety risks.

Theoretical considerations in balance assessment.

Although balance control is an integral component of all daily activities, its complex and flexible nature makes it difficult to assess adequately. This paper discusses balance by examining it in relation to function and the physical environment. Balance is affected by both the task being undertaken and the surroundings in which it is performed. Different tasks and environments alter the biomechanical and information processing needs for balance control. These issues are discussed and a modification of Gentile s Taxonomy of Tasks is suggested for analysis of clinical balance tests, some of which are used as examples.

Contribution of vision and cutaneous sensation to the control of centre of mass (COM) during gait termination.

This study employed manipulation of sensory inputs (vision and plantar-surface cutaneous sensation) during gait termination to elicit insight into the roles played by these sensory systems in the control of gait termination. Attenuation of cutaneous sensation was achieved through hypothermic anesthesia. Visual information was occluded using special glasses. The subjects were asked to walk along an 8 m walkway and during randomly selected trials (25% of trials) to terminate their gait in a predetermined area. The centre of mass (COM) was obtained in order to provide an indication of the efficiency and stability during termination when sensory inputs were manipulated. Lack of visual information delayed the initiation of the slowing down of the COM forward progression and increased the step length of the last step of termination. Additionally, lack of vision resulted in the COM moving closer to the base of support (BOS) during double support and more variability, in the COM, when attempting to achieve a final stable position. Insensitivity of the plantar-surface mechanoreceptors led to a longer second step and a more variable foot placement of the first step, and increased the loading rate during the final two steps of termination. Additionally when vision and cutaneous information were absent the resolution of the final stable position was not as effectively controlled. The results demonstrated that visual information about self-motion and object-motion and sensation from the plantar surface of the foot play phase-specific roles in the control of COM during gait termination.

Effects of head immobilization on the coordination and control of head and body reorientation and translation during steering.

Changing the direction of locomotion involves lateral translation of the body in addition to body reorientation to align with the new travel direction. We designed this study to investigate the CNS control of these postural adjustments. The specific aims of the study were: first, to test the hypothesis that anticipatory head movements towards the new travel path are proactively controlled by the CNS to provide a stable frame of reference for body reorientation and, second, to investigate the relative contribution of foot placement and other mechanisms to the control of lateral body translation during steering. We achieved these aims by carrying out a comprehensive biomechanical analysis of participants performing a steering paradigm and observing the effects of immobilizing the head (by fixing it to the trunk) on postural control and the sequencing of body segment reorientation. Participants performed a task whereby they were visually cued to change their direction of walking by 30 degrees or 60 degrees, left or right, at the midpoint of a 9-m path. The temporal sequence of body reorientation was consistent with previous findings that the head starts to turn in the direction of travel before the rest of the body. Translation of the centre of mass (COM) in the new travel direction was achieved both through alternate placement of the contralateral foot prior to the turn step and use of a hip strategy to control the body pendulum during swing. Immobilizing the head resulted in the following significant changes: earlier onset of trunk yaw with respect to cue delivery, later trunk roll onset and a reduction in trunk roll amplitude. These results provide valuable information regarding the biomechanics of steering and support the hypothesis that aligning the head with motor or locomotor goals using vision provides the CNS with a stable frame of reference, independent of gaze, that can be used to control the repositioning of the body in space.

Ankle muscle stiffness in the control of balance during quiet standing.

This research presents new data and reanalyzed information to refute the criticisms of our model of stiffness control during quiet standing. A re-review of their references to biomechanical research on muscle ankle stiffness confirmed muscle stiffness estimates of the ankle series elastic elements that agreed closely with our estimates. A new technique is presented that directly estimates the muscle stiffness from the ankle moment (N. m) and sway angle (deg). The linear regression of 10 subjects standing quietly for 10 s estimated the stiffness (N x m/deg) to be safely above the gravitational spring. The R(2) scores for this linear regression averaged 0.92, confirming how closely the model approached a perfect spring that would have an R(2) = 1. These results confirm our model of a simple muscle stiffness control and refutes the criticisms.

Control of steering in the presence of unexpected head yaw movements. Influence on sequencing of subtasks.

Control of the head during locomotion has been suggested as a means of facilitating overall postural control of the body. The control of online steering is challenging, as it requires the central nervous system (CNS) to simultaneously control body reorientation in a new direction while modifying the ongoing step cycle. Stable body posture during steering is maintained via appropriately organized postural responses to error signals detected by the visual, vestibular, and/or proprioceptive systems. Modifications to the gait cycle include step-width regulation and movement of body center of mass (COM) in the direction of travel, and may be preceded by independent control of head orientation to see where one is going. The purpose of this investigation was to examine how the ability to successfully steer is influenced by unexpected head perturbations and how various body segments are coordinated and controlled to successfully steer along different pathways. Body kinematics were monitored as participants changed their direction of travel by varying amounts when visually cued one stride before the turn. Perturbations to the head were applied to either assist or oppose the change in direction one step prior to initiation of the turn. Analyses focused on the timing of the changes in head yaw, trunk yaw, and COM trajectories in the mediolateral plane. Results indicate that the order of control over the body segments was head and trunk reorientation in the direction of travel and finally movement of the COM in the intended direction. Thus gaze, inferred from head movement, preceded changes in COM trajectory. This suggests that looking where you are going is critical for steering. When steering is potentially compromised by unexpected head movements, the CNS delays committing movement of the COM until it has a chance to look at the new travel path.

Artificial neural network model for the generation of muscle activation patterns for human locomotion.

Skilled locomotor behaviour requires information from various levels within the central nervous system (CNS). Mathematical models have permitted researchers to simulate various mechanisms in order to understand the organization of the locomotor control system. While it is difficult to adequately characterize the numerous inputs to the locomotor control system, an alternative strategy may be to use a kinematic movement plan to represent the complex inputs to the locomotor control system based on the possibility that the CNS may plan movements at a kinematic level. We propose the use of artificial neural network (ANN) models to represent the transformation of a kinematic plan into the necessary motor patterns. Essentially, kinematic representation of the actual limb movement was used as the input to an ANN model which generated the EMG activity of 8 muscles of the lower limb and trunk. Data from a wide variety of gait conditions was necessary to develop a robust model that could accommodate various environmental conditions encountered during everyday activity. A total of 120 walking strides representing normal walking and ten conditions where the normal gait was modified in terms of cadence, stride length, stance width or required foot clearance. The final network was assessed on its ability to predict the EMG activity on individual walking trials as well as its ability to represent the general activation pattern of a particular gait condition. The predicted EMG patterns closely matched those recorded experimentally, exhibiting the appropriate magnitude and temporal phasing required for each modification. Only 2 of the 96 muscle/gait conditions had RMS errors above 0.10, only 5 muscle/gait conditions exhibited correlations below 0.80 (most were above 0.90) and only 25 muscle/gait conditions deviated outside the normal range of muscle activity for more than 25% of the gait cycle. These results indicate the ability of single network ANNs to represent the transformation between a kinematic movement plan and the necessary muscle activations for normal steady state locomotion but they were also able to generate muscle activation patterns for conditions requiring changes in walking speed, foot placement and foot clearance. The abilities of this type of network have implications towards both the fundamental understanding of the control of locomotion and practical realizations of artificial control systems for use in rehabilitation medicine.

Improvements in clinical and functional vision and quality of life after second eye cataract surgery.

PURPOSE: To determine whether there is a need for second eye cataract surgery or whether cataract surgery in one eye provides sufficiently adequate vision. METHODS: The vision of 43 patients was assessed using a battery of clinical vision tests, performance-based functional vision tests, and quality of life questionnaires, both before and a few months after cataract surgery. Twenty-five patients underwent second eye surgery and 18 patients underwent first-eye surgery. To determine whether cataract surgery returned vision to normal levels, a control group of 25 subjects of a similar age with normal, healthy eyes was also assessed. RESULTS: Overall, greater improvements occurred in most aspects of vision after first eye surgery than after second eye surgery. However, second eye surgery provided similar improvements in mobility orientation and self-reported night driving to those after first eye surgery, and substantially greater improvements in stereoacuity and reductions in anisometropia. CONCLUSIONS: The study provides additional evidence to support the need for second eye cataract surgery. Second eye surgery may be particularly important to improve mobility orientation and the avoidance of falls.

NACOB presentation CSB New Investigator Award. Balance recovery from medio-lateral perturbations of the upper body during standing. North American Congress on Biomechanics.

Postural control strategies have in the past been predominantly characterized by kinematics, surface forces, and EMG responses (e.g. Horak and Nashner, 1986, Journal of Neurophysiology 55(6), 1369-1381). The goal of this study was to provide unique and novel insights into the underlying motor mechanisms used in postural control by determining the joint moments during balance recovery from medio-lateral (M/L) perturbations. Ten adult males received medio-lateral (M/L) pushes to the trunk or pelvis. The inverted pendulum model of balance control (Winter et al., 1998, Journal of Neurophysiology 80, 1211-1221) was validated even though the body did not behave as a single pendulum, indicating that the centre of pressure (COP) is the variable used to control the centre of mass (COM). The perturbation magnitude was random, and the central nervous system (CNS) responded with an estimate of the largest anticipated perturbation. The observed joint moments served to move the COP in the appropriate direction and to control the lateral collapse of the trunk. The individual joints involved in controlling the COP contributed differing amounts to the total recovery response: the hip and spinal moments provided the majority of the recovery (approximately 85%), while the ankles contributed a small, but significant amount (15%). The differing contributions are based on the anatomical constraints and the functional requirements of the balance task. The onset of the joint moment was synchronous with the joint angle change, and occurred too early (56-116 ms) to be result of active muscle contraction. Therefore, the first line of defense was provided by muscle stiffness, not reflex-activated muscle activity.

What guides the selection of alternate foot placement during locomotion in humans.

Our goal was to understand the bases for selection of alternate foot placement during locomotion when the normal landing area is undesirable. In this study, a light spot of different shapes and sizes simulated an undesirable landing area. Participants were required to avoid stepping on this spot under different time constraints. Alternate chosen foot placements were categorised into one of eight choices. Results showed that selection of alternate foot placement is systematic. There is a single dominant choice for each combination of light spot and normal landing spot. The dominant choice minimises the displacement of the foot from its normal landing spot (less than half a foot length). If several response choices satisfy this criterion, three selection strategies are used to guide foot placement: placing the foot in the plane of progression, choosing to take a longer step over a shorter step and selecting a medial rather than lateral foot placement. All these alternate foot-placement choices require minimal changes to the ongoing locomotor muscle activity, pose minimal threat to dynamic stability, allow for quick initiation of change in ongoing movement and ensure that the locomotor task runs without interruption. Thus, alternate foot-placement choices are dependent not only on visual input about the location, size and shape of the undesirable surface, but also on the relationship between the characteristics of the undesirable surface and the normal landing area.

Obstacle crossing in subjects with stroke.

OBJECTIVE: To study the ability of subjects with stroke to successfully step over an obstacle during ambulation. SETTING: A geriatric rehabilitation unit in a tertiary referral hospital. SUBJECTS: Twenty-four inpatients with stroke (median time poststroke 27 days, interquartile range 21 to 44.5 days) able to walk 10 m unassisted without walking aids; also, 22 healthy subjects. METHOD: Subjects were required to step over obstacles of various heights and widths, ranging from 1cm to 8cm. A fail was scored if the obstacle was contacted by either lower limb or if assistance or upper limb support was required. The choice of leading limb and the presence of visual deficits and neglect were also recorded in the stroke subjects. Subjects were tested on two occasions. RESULTS: Significantly more fails were recorded for stroke subjects, with 13 subjects failing at least once. No preference was shown for leading either with the affected or with the unaffected leg. Stroke subjects showed inconsistent performance over the two testing sessions. CONCLUSION: The ability to negotiate obstacles was compromised and inconsistent in stroke subjects undergoing inpatient rehabilitation. This suggests that gait safety in this population remains threatened.

Altered kinetic strategy for the control of swing limb elevation over obstacles in unilateral below-knee amputee gait.

Our goal was to document the kinetic strategies for obstacle avoidance in below-knee amputees. Kinematic data were collected as unilateral below-knee traumatic amputees stepped over obstacles of various heights in the walking path. Inverse dynamics were employed to calculate power profiles and work during the limb-elevation and limb-lowering phases. Limb elevation was achieved by employing a different strategy of intra-limb interaction for elevation of the prosthetic limb than for the sound limb, which was similar to that seen in healthy adult non-amputees. As obstacle height increased, prosthetic side knee flexion was increased by modulating the work done at the hip, and not the knee, as seen on the sound side. Although the strength of the muscles about the residual knee was preserved, the range of motion of that knee had previously been found to be somewhat limited. Perhaps more importantly, potential instability of the interface between the stump and the prosthetic socket, and associated discomfort at the stump could explain the altered limb-elevation strategy. Interestingly, the limb-lowering strategy seen in the sound limb and in non-amputees already features modulation of rotational and translational work at the hip, so an alternate strategy was not required. Thus, following a major insult to the sensory and neuromuscular system, the CNS is able to update the internal model of the locomotor apparatus as the individual uses the new limb in a variety of movements, and modify control strategies as appropriate.

Online steering: coordination and control of body center of mass, head and body reorientation.

Steering is an integral component of adaptive locomotor behavior. Along with reorientation of gaze and body in the direction of intended travel, body center of mass must be controlled in the mediolateral plane. In this study we examine how these subtasks are sequenced when steering is planned early or initiated under time constraints. Whole body kinematics were monitored as individuals were required to change their direction of travel by varying amounts when visually cued either at the beginning of the walk or one stride before. The analyses focused on the transition stride from one travel direction to another. Timing of changes (with respect to first right foot contact) in trunk roll angle, head and trunk yaw angle, and right foot displacement in the mediolateral plane were analyzed. The magnitude of these measures along with right and left foot placement at the beginning and right foot placement at the end of the transition stride were also analyzed. The results show the CNS uses two mechanisms, foot placement and trunk roll motion (piking action about the hip joint in the frontal plane), to move the center of mass towards the new direction of travel in the transition stride, preferring to use the first option when planning can be done early. Control of body center of mass precedes all other changes and is followed by initiation of head reorientation. Only then is the rest of the body reorientation initiated.

Low back three-dimensional joint forces, kinematics, and kinetics during walking.

OBJECTIVE: The purpose of this study was to examine the three-dimensional low back loads, spinal motions, and trunk muscular activity during gait. Specific objectives involved assessment of the effects of walking speed, and arm swing on spinal loads, lumbar spine motion, and muscular activation. DESIGN: An in vivo modeling experiment using five male participants. Thirty walking trials were performed by each participant yielding five repeats of each condition (3 walking cadences x 2 arm swing conditions). BACKGROUND: Walking is often prescribed as a rehabilitation task for individuals with low back injuries. However, there are few studies which have examined the joint loading, spinal motions, and muscular activity present when walking. Additionally, the majority of studies examining spine loading during gait have used an inverse dynamics model, commencing at the cranial aspect of the body, approach which does not include the impulsive phases of gait (i.e. heel strikes and toe offs). METHODS: Low back joint forces (bone on bone) and moments were determined using an anatomically complex three-dimensional model (detailing 54 muscles and the passive structures acting at the low back) during three walking cadences and with free arm swing or restricted arm swing. In order to assess the influence of the transient factors such as heel contact on the joint forces a bottom up (from the feet to the lumbar spine) rigid link segment analyses approach was used as one input to the three-dimensional anatomic model. Lumbar spine motion and trunk muscle activation levels were also recorded to assist in partitioning forces amongst the active and passive tissues of the low back. RESULTS: Net joint anterior-posterior shear loading was the only variable significantly affected by walking cadence (fast versus slow P < 0.0003). No variable was significantly affected by the arm swing condition. Trends demonstrated an increase in all variables with increased walking cadence. Similarly, most variables, with the exception of axial twist and lateral bend lumbar spine motion and lateral joint shear, demonstrated increasing trends caused by the restriction of normal arm swing. CONCLUSIONS: Tissue loading during walking appears to be below levels caused by many specific rehabilitation tasks, suggesting that walking is a wise choice for general back exercise and rehabilitation programs. Slow walking with restricted arm swing produced more 'static' lumbar spine loading and motion patterns, which could be detrimental for certain injuries and tissues. Fast walking produced a more cyclic loading pattern.