By Keisuke Hirata. 

Walking on a split-belt treadmill (Figure 1A) is a well-established method to investigate motor adaptation during locomotor tasks. Although previous studies reported the symmetry of step length as a critical measure of adaptation, the relative contribution of the lower limb joints remains unclear. This is relevant because clarifying the effect of split-belt training on joints and preselecting patients to be applied. In this study, we measured the hip, knee, and ankle joint angles using a motion capture system during split-belt treadmill walking to determine which joints facilitate adaptation of gait (Figure 1B).

Ten healthy young adults participated in the study. They walked under a symmetric and asymmetric condition on a split-belt treadmill. During the symmetric condition, both belts moved at 0.9 m/s. In asymmetric condition, one belt moved at 0.9 m/s while the other moved at 1.8 m/s (Figure 1C). After a 3-min adaptation period, participants walked with symmetric step length, which was consistent with results from previous studies. Our kinematic analysis showed that the left and right knee and ankle joint angles were asymmetric when the foot made initial contact, while the hip joint angles remained symmetric (Figure 1D). Our result suggests that the more forward foot contact position of the faster side was due to increased extension of the knee, but not the hip.

Our findings suggest that people mainly alter their knee joint angles to adapt to split-belt treadmill walking. This increases our understanding of gait adaptation. It is also clinically relevant since researchers and clinicians are starting to use the split-belt paradigm as a rehabilitation tool. Our results suggest that they should consider the function of each of the patient’s joints as the results of the split-belt rehabilitation may be limited for patients with impaired knee joints.

Publication

Hirata K, Kokubun T, Miyazawa T, Yokoyama H, Kubota K, Sonoo M, Hanawa H, Kanemura N (2018). Contribution of lower limb joint movement in adapting to re-establish step length symmetry during split-belt treadmill walking. J Med Biol Eng. doi: https://doi.org/10.1007/s40846-018-0456-0

Figure 1. A: The experiment was performed on a split-belt treadmill, where a left and a right belt can move at different speeds. B: Definitions of the angles and step length at foot contact. C: Gait protocol and data collection periods; the two belts started at similar speed for 1 minute, after which the fast side belt speed was increased. D: Joint angles at foot contact during initial contact of the leg on the slow (top left) and fast (bottom left) side of the treadmill during the last 10 strides in the asymmetric condition, and a typical example of the lower joint angles at foot contact on the fast and slow side during the experimental (right).

About the Author

By Dr Chris McCrum.

To improve the effectiveness of fall prevention interventions, we need to better understand how to encourage long-term improvements in walking stability. Part of that involves how we train people to cope with sudden, unexpected disturbances such as trips and slips. Another factor is if the training effects can be transferred to benefit other tasks. In this study, we aimed to investigate how short-term improvements in coping with repeated, sudden disturbances to one leg during walking would be “remembered” after one month, and if the untrained leg would benefit from the trained leg’s experience.

To achieve this, we had eighteen healthy young adults walk on a dual-belt treadmill (individual belts under each foot). During about 14 minutes of walking, we applied ten unexpected treadmill belt accelerations (the first and last perturbing the right leg, the others perturbing the left leg). We repeated this assessment after one month. We used the margin of stability (MoS) to assess how the stability of the body configuration (accounting for centre of mass velocity) changed during the first eight steps following the first and last perturbation to each leg, on each day. We found significant improvements in MoS on the first day for perturbations to the trained leg (Figure A), but the untrained leg showed no differences before and after the training (Figure B). On the second day, the first perturbation to the trained leg led to a very similar response to the post-training state on day one, indicating almost full retention of the training effects, one month later (Figure C).

Our findings demonstrated that gait perturbations can stimulate large training effects that can be retained over time. The almost fully retained training effect after one month of not training shows that the task is promising for falls prevention interventions, where long-term effects are very important. However, these effects were not transferable across limbs, despite the whole-body nature of the task. This suggests that interventions focusing on improving reactive gait stability should incorporate perturbations to both limbs. An open question for future research is whether the training effects after only eight perturbations could be transferred or generalised to other similar gait stability tasks such as overground trips or slips during daily life activities.

Figure: Margins of stability during baseline walking (Base), one step before perturbation (Pre) and during the first eight recovery steps (Post1-8). Panel A: the first and final perturbation to the trained leg on day 1, B: the first and final perturbation to the untrained leg on day 1, and C: the final perturbation to the trained leg on day one and the first perturbation to the trained leg on day 2, one month later. Bars indicate significant differences to Base within the indicated perturbation and * indicates significant differences between perturbation for the indicated step. Figure adapted from McCrum et al. (2018).

Publication

McCrum M, Karamanidis K, Willems P, Zijlstra W, Meijer K. (2018) Retention, savings and interlimb transfer of reactive gait adaptations in humans following unexpected perturbations. Communications Biology, 1:230. doi: 10.1038/s42003-018-0238-9 https://www.nature.com/articles/s42003-018-0238-9

About the Author

Many neurological disorders lead to gait and balance impairments. Especially in older people, these disorders are a common cause of falls, associated with significant morbidity and mortality. Despite the recognition of the socio-economic burden of falls, there are very few treatment options beyond physical therapy for neurological gait and balance impairment. From a brain perspective, human locomotion relies upon a distributed neural network including primary motor, premotor areas, basal ganglia and, importantly, white matter connections between these areas. White Matter hyperintensities and other changes in the cerebral white matter (‘leukoaraiosis’) are very common in old age and associated with gait and balance dysfunction.

This review paper explores whether beneficial effects of physical training can be enhanced by using non-invasive brain stimulation, namely transcranial direct current stimulation (tDCS), in patients with neurological gait disorders. tDCS is a non-invasive neurostimulation technique that consists of delivering a weak electrical current through the scalp. This has been shown to induce bidirectional polarity-dependent changes in excitability of the underlying cortex; anodal tDCS increases cortical excitability and cathodal tDCS decreases it. The physiological and behavioural effects of tDCS have been shown to last for up to one hour, implying that tDCS also modulates the synaptic strength of intracortical and corticospinal neurons.

Across a number of our own pilot studies, we explored whether these physiological and behavioural effects may facilitate neuroplasticity during physical therapy and thus enhance its effectiveness. We applied 15 minutes of anodal tDCS over the motor and premotor cortex of both cerebral hemispheres using a central electrode in patients with Parkinson’s disease and patients with leukoaraiosis while they were also receiving gait and balance physical therapy. We found that the combination of cortical stimulation and physical therapy improved gait velocity, stride length, time taken to complete the ‘Timed Up and Go’, and postural reactions, above and beyond the positive effects of physical therapy alone. tDCS alone (without physical therapy), however, did not improve gait in patients with Parkinson’s disease or leukoaraiosis.

Our review paper and pilot studies suggest that non-invasive brain stimulation (such as tDCS) may enhance the effects of physical therapy in patients with neurological gait disorders. Large-scale, multicenter, randomized, double-blind, Phase III studies using standardized protocols based on the more robust published pilot data are needed before these techniques can be implemented into mainstream clinical practice.

Figure 1. A tDCS stimulation protocol showing anodal tDCS stimulation over the primary motor and pre-motor cortices bilaterally, and reference (cathode) electrode (blue rectangle), over the inion. B Hypothesized effect on synaptic excitability depicting the additive effect of physical therapy and tDCS (red arrow) in lowering the threshold of a motor action potential (i.e. increased cortical excitability), leading to increased cortical plasticity over motor cortical regions, and improved clinical outcomes. C Mean averaged data across pilot studies discussed in the main text, showing the largest reduction in time taken to walk 6 metres in the tDCS + physical therapy arm, compared to physical therapy with sham stimulation.

Publication

Kaski D, Bronstein AM, 2014, Treatments for Neurological Gait and Balance Disturbance: The Use of Non-invasive Electrical Brain Stimulation, Advances in Neuroscience, Vol: 2014, Pages: 1-13, ISSN: 2356-6787

About the Author

Multiple sclerosis (MS) is characterized by central nervous system white matter lesions that affect people’s ability to move independently. Further, people with MS often report significant asymmetries in muscle strength and function in the left versus the right leg. These are often associated with increased postural sway (i.e. worse balance) and less symmetrical stepping patterns during walking (i.e. worse walking). It is no surprise that such lower limb asymmetries are frequently associated with poorer balance control, falls, and reduced quality of life. Currently there is limited understanding as to why these limb asymmetries exist in MS and which areas within the central nervous system contribute to these mobility-limiting issues. It is also unknown whether improving these lower limb asymmetries may concomitantly improve balance and mobility during activities of daily living.

To address these questions, participants stood on a platform and tried to maintain their balance while the  platform continually slid forward and backward at a fixed frequency of differing amplitudes. We measured their ability to anticipate changes in direction (i.e. temporal performance) and their ability to control the amplitude of sway (i.e. spatial performance) with repeated exposures to this moving platform. To understand the neural underpinnings of postural motor learning, we correlated the acquisition and retention of practice-related improvements in postural control to brain white matter microstructural integrity acquired via diffusion weighted magnetic resonance images using a tract-based spatial statistical approach. Despite having worse postural control than control participants, those with MS exhibited improvements in temporal performance (over one day of practice) and retention (ability to maintain improvements 24 hours later) in a similar manner as control participants. Improvements in temporal performance were directly correlated to microstructural integrity of white matter tracts in the corpus callosum, posterior parieto-sensorimotor fibers and the brainstem in people with MS. Within the corpus callosum, fibers connecting the primary motor cortices (red fibers in Figure 1)were most strongly correlated to temporal improvements in postural control, in contrast to those connecting pre-supplementary or supplementary motor areas (yellow and orange fibers in Figure 1).

For movements that require precise coordination between the two sides of the body (e.g. walking, postural control of balance, typing) a delicate balance of excitation and inhibition is required between the right and left sensorimotor cortices. This interhemispheric communication is principally accomplished through the corpus callosum. Reduced quality of the corpus callosum is common in people with MS and has been directly related to poorer communication between the two sides of the brain and upper extremity motor performance. We suggest that impairments in gait and balance control are also, at least in part, a result of reduced structure and altered communication between the two sides of the brain in people with MS. However, our understanding of how changes in communication between the two sides of the brain contribute to lower limb asymmetries and the resultant declines in mobility for those with MS remains incomplete.

Figure 1 – Interhemispheric white matter fiber tracts connecting the right and left pre-supplementary motor areas (yellow), supplementary motor areas (orange), and primary motor cortices (red).

Copyright:

The ISPGR blog applied Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license to figure and text of the article.

https://creativecommons.org/licenses/by-sa/4.0/

Publication:

Daniel S. Peterson, Geetanjali Gera, Fay B. Horak, Brett W. Fling. Corpus Callosum Structural Integrity Is Associated With Postural Control Improvement in Persons With Multiple Sclerosis Who Have Minimal Disability. Neurorehabilitation and Neural Repair, Vol 31, Issue 4, pp. 343 – 353

http://journals.sagepub.com/doi/abs/10.1177/1545968316680487

About the Author

Step training has recently been shown effective in preventing falls most likely because of its high task-specificity to rapid movements required to avoid falls. Step training systems using interactive video game technology have the potential for widespread implementation because they are low-cost and can be used unsupervised by older people at home. While this is all very promising, there is one thing we need to consider. Most stepping systems only train in a few directions (e.g., anterior-posterior and lateral directions). This is concerning because a randomised controlled trial (RCT) showed that upper-limb resistance training with limited directions deteriorated rapid movements in untrained directions in older adults. Therefore, to ensure the safety of home-based step training system, we conducted this study to examine transfer effects of step training on stepping performance in untrained directions among older adults.

We conducted an RCT with 54 older adults aged 65 years or older. The participants were randomly allocated to one of three groups; forward step training (FT), lateral plus forward step training (FLT) and no training (NT) groups. A choice stepping reaction time (SCRT) system was used for the training as well as assessments (see Figure). The FT group completed 200 forward steps, while the FLT group completed 100 forward steps and 100 lateral steps. The NT group rested for 15-min between the pre- and post-assessments. Prior to and immediately after the training or rest periods, the participants underwent a 2-min CSRT assessment. During the assessments, participants wore 14-mm diameter reflective markers to the lower limbs and their stepping movements were recorded using a 6-camera Vicon Bonita motion capture system. We used choice stepping reaction time and stepping kinematics in untrained, diagonal and lateral directions as outcome measures. Results indicated that FT induced delayed response time (a negative transfer effect) and faster peak stepping speed (a positive transfer effect) in the diagonal direction during the first step after the training. However, these effects were no longer apparent in the subsequent steps. Moreover, no such effects were seen in the FLT group.

Figure. A) The step mat and screen display used in the step training and stepping performance assessments. B) A typical example of stepping trajectory for one participant.

Our results suggest that if participants receive a step training program that only trains steps in the forward direction, this will improve stepping speed but may acutely slow response times in the untrained diagonal direction. However, this acute effect appears to dissipate after a few repeated steps. Step training in both forward and lateral directions appears to induce no negative transfer effects in untrained diagonal stepping. These findings suggest home-based step training systems (usually with 6 directions) present low risk of harm through negative transfer effects in untrained stepping directions.

Publication

Okubo Y, Menant J, Udyavar M, Brodie MA, Barry BK, Lord SR, Sturnieks DL. Transfer effects of step training on stepping performance in untrained directions in older adults: A randomized controlled trial. Gait & Posture 54 (2017) 50–55

http://www.gaitposture.com/article/S0966-6362(17)30048-6/abstract

About the Author

Being able to adjust our walking pattern is crucial when performing daily living activities such as crossing a busy street or avoiding obstacles. Poor walking performance might contribute to tripping, which is a frequently reported cause of falls in older people. We recently devised a walking task that is able to assess an individual’s ability to adapt to environmental hazards. This new test requires people to either step onto a target or avoid an obstacle appearing on the pathway just before they reach it (i.e. two steps ahead). Our aim was to compare the adaptive walking strategies of young and older adults when performing this task.

Fifty healthy older adults and 21 young adults initially walked over an obstacle-free path (baseline walking). They then completed the following randomly presented adaptive walking trials: obstacle avoidance, short stepping target, long stepping target and no target/obstacle (walk-through) trials (see figure for details). Older adults adopted a more cautious walking strategy, which was characterized by slower gait speed, shorter step length and a longer time spent in double support when they approached the targets/obstacle. However, despite this cautious strategy, older adults made more mistakes (failed to hit the stepping targets and/or to avoid the obstacle) and were less accurate to step on the centre of the target than young adults. In addition, young individuals maintained the same walking pattern for both the baseline and walk-through conditions, whereas older participants reduced their step length and gait speed and increased their double-support time significantly in the walk-through condition.

The older adults adopted a conservative walking pattern throughout the experiment, even when a target/obstacle was not presented (walk-through condition). Older adults might therefore be more affected by the possibility of a hazard appearing on the pathway than young adults. The same conservative walking strategy was also detected for each target/obstacle condition in the older group. However, despite this strategy, older adults still had a poorer stepping accuracy and made more mistakes. This reduced ability to adjust walking performance when needed may place older adults at increased risk of falling when unexpected hazards appear, such as a suddenly noticed crack in the pavement. Our findings may contribute to the development of new strategies for improving adaptive walking performance in the older population and may assist the efficacy of fall prevention programmes. New strategies could include the decision-making component and/or obstacle avoidance/stepping target training while walking. Future studies should investigate whether our test paradigm can predict future falls, and also whether walking adaptability training can improve both task performance and prevent future falls.

Figure. Typical walking performance of a younger adult (A) and an older adult (B) for each condition (baseline, walk-through, obstacle avoidance, short target and long target. Obstacle position is showed in the baseline and walk-through conditions as a representation of its location. No stimulus was triggered for those conditions. The target/obstacle appearance was triggered on the heel strike of the footfall indicated by the dashed red boxes.

Publication

Caetano MJD, Lord SR, Schoene D, Pelicioni PHS, Sturnieks DL, Menant JC. Age-related changes in gait adaptability in response to unpredictable obstacles and stepping targets. Gait Posture 2016; 46:35-41. http://www.gaitposture.com/article/S0966-6362(16)00044-8/abstract

About the Author