• 31 Jul 2017 by Hanatsu Nagano

    For the senior population, fall-related injuries often lead to loss of independent lifestyles and enormous medical costs. Tripping is the leading cause of falls, and often results in a forward loss of balance. Dynamic balance after a trip could still be restored by an effective recovery step to prevent the fall. The effectiveness of the recovery step depends on both position and timing factors – the foot should be ‘positioned sufficiently” in front of the whole body centre of mass within a certain ‘time limit’. In the process of balance recovery, the recovery leg needs to absorb the falling momentum by knee and ankle eccentric work. We aimed to identify the biomechanical requirements of such recovery steps during unanticipated forward falling in older adults. For this investigation, biomechanical characteristics of the initial recovery step were compared between single- and multi-step recovery actions. A single step recovery should essentially fulfil all requirements of balance restoration, while a multi-step recovery distributes the entire burden over several steps. Compared to multi-step recoveries, the single-step response was, therefore, hypothesised to play a larger role for balance recovery.

    We employed a commonly-used tether-release protocol to test our hypothesis. Fifteen healthy older participants maintained forward leaning position with a cable supporting them from the back (see figure). At random timing, the cable was released to induce a forward fall, essentially requiring recovery actions. These recovery actions were recorded using a Vicon 3D motion capture system and AMTI force platforms to analyse the biomechanical characteristics of the recovery steps. We determined the margin of stability as the distance from the extrapolated centre of mass position to the base of support boundary, indicating spatial stability. Dynamic balance is secured when margin of stability is positive. Available response time was computed as the estimated time for centre of mass to reach the base of support boundary.

    Figure: (left) whole body model during a multiple-step recovery, (right) ankle and knee eccentric work and power absorption during the first recovery step.


    For both single and multiple step responses, the margin of stability was negative at recovery foot contact, which indicates that balance was not yet secured. To avoid a fall, a positive margin of stability should be established within available response time, which was on average 0.204s in the single step responses. Correlation analysis suggested that knee and ankle eccentric work may absorb the excessive falling momentum. Larger step length and velocity were also found to possibly support balance recovery. Practical training for effective recovery step may, therefore, incorporate eccentric work of the stepping limb while other concentric actions would be also important for limb swing to achieve long fast recovery step. Future studies should test this hypothesis in populations with lower limb joint degeneration (e.g. osteoarthritis patients).

     

    Publication

    Nagano, H., Levinger, P., Downie, C., Hayes, A., Begg, R.K. 2015. Contribution of Lower Limb Eccentric Work and Different Step Responses to Balance Recovery among Older Adults. Gait and Posture, 42 (3): 257-262. DOI: 10.1016/j.gaitpost.2015.05.014

     

    The author

    Dr Hanatsu Nagano

    Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, Melbourne, Australia.

     

    Dr Nagano is a postdoctoral research fellow at the Institute of Sport, Exercise and Active Living. His area of expertise is gait biomechanics specialising in falls prevention among senior adults. He is an honorary physiologist at Austin Health.

     

    Copyright

    © 2017 by the author.

    Except as otherwise noted, this blog, including its text and figures, is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/legalcode.

     

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  • 26 Jul 2017 by Joe Verghese

    Falls are increasingly prevalent with advancing age and the consequences are often devastating, resulting in loss of independence, institutionalization and premature mortality. Evidence supports impairments in cognitive functions, specifically executive functions, as major contributors to falls. Worse performance on dual-task assessments that involve executive functions, such as walking while performing an attention demanding task, predict falls in non-demented older adults. The prefrontal cortex (PFC), a key structure for performing executive functions, also plays a vital role in control of cognition and mobility, indicating its important role in fall risk. Although the PFC is recognized as a potentially important contributor to falls, conventional neuroimaging techniques cannot image the brain during motion, leaving a gap in the understanding of underlying neural processes that might predict fall risk, and necessitated the use of newer approaches that can be used to study people while they walk, such as the functional Near Infrared Spectroscopy (fNIRS).

    The primary goal of the study was to determine whether brain activity in the PFC measured during walking predicts falls in high-functioning older adults. We selected a high-functioning group of community-dwelling older adults enrolled in a prospective aging study at Albert Einstein College of Medicine to evaluate early brain activation changes that predict falls. Task-related changes in oxygen levels in the PFC were measured using fNIRS during single-task conditions (normal pace walking and standing while reciting alternate letters of the alphabet), and a dual-task condition (walking while reciting alternate letters of the alphabet). Over the 50-month study period 71 of the 166 participants reported 116 falls. People who had increases in brain activity levels during the dual-task condition were 32 percent more likely to fall. Brain activity levels during both the cognitive or motor single task conditions did not predict fall risk.

    These findings provide evidence that brain activity patterns during cognitively demanding assessments predict falls in older adults and may not be elicited by more simple tasks. From a clinical perspective, these findings suggest that there may be changes in brain activity before visible signs of clinical dysfunction and physical symptoms manifest in high-functioning people who are at risk of falls. In the future, a brain scan assessment such as fNIRS might be used to help predict falls in older adults. Clinicians may be able to use this information to recommend behavioral and lifestyle modifications or treatments for their patients that may reduce the risk of future falls.

    Figure 1. Participant completing fNIRS assessment.

     

     

    Publication:

    Verghese J, Wang C, Ayers E, Izzetoglu M, Holtzer R. Brain activation in high-functioning older adults and falls Prospective cohort study. Neurology. 2017 Jan 10;88(2):191-7. http://www.neurology.org/content/88/2/191

    Authors:

    Emmeline Ayers, MPH and Joe Verghese, MBBS

    Affiliations:

    Departments of Neurology1 and Medicine,2 Albert Einstein College of Medicine, Bronx, New York, USA

    Bios:

    Emmeline Ayers is an Associate, The Saul R. Korey Department of Neurology. Her research interests are in understanding the role of gait and mobility in progression to dementia and cognitive decline in older adults.

    Dr. Verghese is Professor of Neurology and Medicine, Murray D. Gross Memorial Faculty Scholar in Gerontology, Director, Resnick Gerontology Center, and Chief of the Integrated Divisions of Cognitive and Motor Aging (Neurology) and Geriatrics (Medicine). He is an expert in aging and the effects on mobility and cognition.

     

     

     

     

     

     

     

     

     

    Copyright

    © 2017 by the author.

    Except as otherwise noted, this blog, including its text and figures, is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/legalcode.

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  • 19 Jun 2017 by Natalia Rinaldi

    Older adults with history of falls often slow down and have a more variable gait when performing another task at the same time (dual task walking). However, most studies involving dual task paradigms have investigated primarily the walking task, while little attention has been given to performance in the secondary task. The combined task of walking while reaching and grasping an object (prehension) is widely performed during daily life activities, such as picking up a glass, shopping, eating, and others. Importantly, older adults need to adapt their walking patterns to make sure that their gait is stable while conducting such a prehension task. Our study investigated the level of interference between the combined task of walking and prehension with different levels of manual task difficulty.

     

    Fallers and non-fallers were invited to perform three tasks: (1) simple walking (control condition), (2) reaching-to-grasping a dowel during quiet standing, and (3) grasping a dowel wile walking. The dowel was placed on a cylindrical support with different types of bases (wide and narrow) and was surrounded by two obstacles with two different distances between them (short and long). Whole body center of mass and spatiotemporal gait parameters were analyzed to explore changes in walking, reaching (duration and velocity) and grasping (hand grip aperture and velocity). Participants with history of falls walked slower and took wider steps during the dual task walk for the most difficult manual conditions. While reaching, fallers also reduced their body velocity and increased the body stability (margin of dynamic stability) to grasp the dowel compared to non-fallers. When looking at the center of mass anterior-posterior velocity, fallers almost stopped walking to perform the prehension task. Fallers presented slower movement time and lower peak wrist velocity, peak grip aperture velocity, and time-to-peak grip aperture, which indicated a generalized slowing down in movement performance.

     

    In conclusion, fallers showed a more conservative walking strategy. They also decoupled the prehension task from the walking when compared to non-fallers and had to increase body stability in order to perform grasping successfully. Our results suggest that manual tasks may be used as an assessment tool for fall risk prediction. Given that prehension movement is widely used during daily life activities, we suggest that preventive and rehabilitation programs should also emphasize movement exercises to improve the control of upper limbs, especially while performing locomotor tasks. 

     

     

     

     

     

     

     

     

     

    Publication:

    Rinaldi NM, Moraes, R. Older adults with history of falls are unable to perform walking and prehension movements simultaneously. Neuroscience. 2016; 249-260.

    http://www.sciencedirect.com/science/article/pii/S0306452215011306

     

    The author:

    Dr Natalia Madalena Rinaldi is a Professor in the Center of Physical Education and Sports of Federal University of Espirito Santo, Brazil. Her research focuses on the effects of aging on gait and posture and the effects of motor interventions to improve the functional capacity in older adults (natalia.rinaldi@ufes.br).

     

     

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  • 12 Jul 2017 by Avril Mansfield

    People who have had a stroke fall frequently. Many previous studies with older adults have found that exercise, particularly balance training, reduces fall risk. However, comparable studies in stroke survivors indicate that similar exercise training does not prevents falls in this group. People fall when they fail to recover from a loss of balance. Recently, studies have found that ‘perturbation-based balance training’ (PBT), which involves people experiencing repeated balance losses, can improve control of reactions to a loss of balance. Some studies have found that PBT reduces fall rates in healthy older adults or in people with Parkinson’s disease. We wanted to know if PBT could reduce fall rates in people with sub-acute stroke.

     

    Physiotherapists at our institution had started PBT with some of their eligible clients as part of routine care for stroke rehabilitation. Therefore, we conducted a non-randomized study to establish the benefit of PBT compared to non-PBT rehabilitation. We recruited participants with sub-acute stroke at discharge from in-patient rehabilitation if they completed PBT during their routine rehabilitation. We then asked these individuals to report any falls that they experienced in the following six months. We compared fall rates to a matched historical control group who were recruited for another study before physiotherapists had implemented PBT, but who also reported falls in daily life for six months after discharge. Five (out of 31) participants in the PBT group reported 10 falls in the six months post-discharge, whereas ten (out of 31) participants in the historical control group reported 31 falls in the six months. The fall rates in the PBT group were significantly lower than in the control group, when accounting for some characteristics that differed between the two groups at baseline.

     

    The results of this study suggest that PBT might help to prevent falls in people with sub-acute stroke. Because the study was not randomized, the results should be interpreted with some caution. However, since the results are consistent with other studies showing reduced fall rates with PBT, the evidence from this study may be sufficient to recommend PBT in clinical practice. Other studies of PBT used programmable treadmills or custom-built moving platforms to provide the balance perturbations in training. In the current study, the physiotherapist provided manual perturbations (e.g., push or pull; see Figure). This meant that PBT only required equipment that is already in most physiotherapy practices. For this reason, we think it would be relatively easy to implement our PBT program in other settings.

     

     

    Figure: Physiotherapist delivers a rightward pull perturbation while the participant walks over foam obstacles.

     

    Publication

    Mansfield A, Schinkel-Ivy A, Danells CJ, Aqui A, Aryan R, Biasin L, DePaul VG, Inness EL. Does perturbation training prevent falls after discharge from stroke rehabilitation? A prospective cohort study with historical control. J Stroke Cerebrovasc Dis. 2017; doi: 10.1016/j.strokecerebrovasdis.2017.04.041

     

    The author

    Avril Mansfield; Scientist, Toronto Rehabilitation Institute – University Health Network; Affiliate Scientist, Evaluative Clinical Sciences, Hurvitz Brain Sciences Program, Sunnybrook Research Institute; Associate Professor (status only), Department of Physical Therapy, University of Toronto

    Avril’s research aims to determine how aging and neurologic injury or disease affect balance control and mobility, and how to exploit principles of optimal learning to develop exercise programs that improve balance and mobility. She is particularly interested in applying this work to develop clinically feasible fall-prevention programs.

     

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  • 17 Jun 2017 by Dominic Pérennou

    Following a stroke, it is important to assess a person’s perception of verticality. This assessment can help us to find what causes the bodily disorientation with respect to vertical (lateropulsion) and can guide post-stroke rehabilitation and monitor postural recovery. The visual vertical (VV) is the most commonly used test to assess verticality perception, both in research and in clinical practice. It is a simple test that consists of adjusting a luminous rod to the vertical in darkness; however, specific guidelines for use in clinical practice are lacking. Published studies have used different methodologies and the impact of these different methodologies on the assessment outcome is not well-understood. For example, should the trunk and head be free to move during the test or should they be fixed in the upright position? This question is critical for stroke survivors. It is well-known that spontaneous lateral whole body tilts are common after stroke and this may compromise their ability to sit on their own and might further impact their perception of verticality. In the present study, we aimed to analyse the impact of controlling body orientation on stroke patients’ ability to estimate VV and their ability to sit unsupported.

     VV perception was assessed in 20 controls and 36 subacute patients undergoing rehabilitation after a first hemisphere stroke, under 3 different scenarios: body not fixed (trunk and head free), partially fixed (trunk fixed, head free), or both trunk and head were fixed. We quantified both trunk and head orientations and analysed VV as a function of trunk and head tilt. Patients were classified into 2 groups according to their ability to maintain (n=25) or not (n=11) an independent upright sitting posture. Our results confirmed for the first time the clinical intuition: it is spontaneous upright trunk (and not head) orientation which is necessary for recovering an independent sitting posture after stroke. This suggests that postural orientation deficits, especially trunk orientation, are a major cause of lateral postural disorders after a stroke. The level of fixation strongly affects the estimation of VV in stroke patients who have difficulties maintaining a seated posture. Our results suggest that a fixed trunk and head in the upright position was the most optimal setting for assessing VV. We proposed that measuring VV without any body fixation is only valid in patients with satisfactory balance abilities. Our results contribute to a better standardization of VV assessment to optimize its integration in research and clinical practice.

    Figure. Individual mean spontaneous orientations of trunk axis and head axis. The data were classified from the most pronounced contralesional tilt (negative values) to the most pronounced ipsilesional tilt (positive values), for trunk orientation, and this order was maintained for the classification of head orientation data. (B) Visual vertical perception, orientation (mean) and uncertainty (variability) as a function of group and setting.

    Publications

    Piscicelli C, Barra J, Sibille B, Bourdillon C, Guerraz M, Pérennou D. (2016). Maintaining trunk and head upright optimizes visual vertical measurement after stroke, Neurorehabil Neural Repair, 30(1):9-18. https://doi.org/10.1177/1545968315583722

    Piscicelli C, Pérennou D. (2017). Visual verticality perception after stroke: A systematic review of methodological approaches and suggestions for standardization. Ann Phys Rehabil Med, 11. pii: S1877-0657(16)00042-7. https://doi.org/10.1016/j.rehab.2016.02.004

     

    The authors

     

     

     

     

     

     

     

     

    Céline Piscicelli and Dominic Pérennou
    Department of NeuroRehabilitation, Institute of Rehabilitation, University Hospital Grenoble-Alpes

    Laboratory Psychology and Neurocognition, UMR 5105 CNRS and Grenoble-Alpes University, Grenoble, France.

    Celine Piscicelli received her PhD in Cognitive Psychology and Neuroscience from Grenoble-Alpes University. She currently works as a neuropsychologist in the Physical and Rehabilitation Medicine Unit at University Hospital Grenoble-Alpes and is an associate member in the Psychology and Neurocognition Lab at Grenoble-Alpes University. Her research focuses on spatial cognition and its interaction with posture and action.  

    Dominic Pérennou is Professor of Medicine, Chair of Physical Medicine and Rehabilitation at Grenoble-Alpes University, and head of the Department of Neurorehabilitation at the University Hospital Grenoble-Alpes (France). He is Editor in Chief of the Annals of Physical Medicine and Rehabilitation, and Associate Editor of Gait & Posture. His main research focuses on internals models of verticality for postural and gait control.

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  • 14 Jun 2017 by Yoshiro Okubo

    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

     

    The author

    Yoshiro Okubo, Postdoctoral Fellow, Falls, Balance and Injury Research Centre, Neuroscience Research Australia

     

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  • 12 Jun 2017 by Gammon Earhart

    People with Parkinson disease (PD) often report difficulty walking as an early and troublesome problem.  Emergence of gait problems is considered a red flag indicating onset of disability, and can contribute to reduced quality of life.  Gait in people with PD is often slower, with reduced stride lengths and increased variability that may be attributed to loss of ability to maintain a steady gait rhythm.  To address this loss of rhythmicity, many studies have employed use of external rhythmic cues, such as music or a metronome, to help stabilize gait.  However, we know very little about the impact of self-generated rhythmic cues, such as singing, on gait.  The goal of this study was to test the feasibility of singing during walking in people with PD, gathering preliminary evidence regarding the efficacy of this novel cueing technique.

     

    Twenty-three people with Parkinson disease participated.  Each person walked at their normal, comfortable pace for the Baseline condition, which was used to determine preferred walking cadence.  Cue rate, or beats per minute of the song, was then set to match preferred cadence.  Participants then walked in three cued conditions and a dual task condition (see Figure).  When walking to music, participants maintained velocity but increased spatial and temporal variability.  Variability was further increased when participants walked while singing along to music.  Singing in the absence of music, however, did not increase variability.  In contrast, when dual tasking (i.e. completing a word generation task while walking) participants showed reductions in velocity along with large increases in variability. 

     

    Of all the conditions tested, singing was the only cue condition that did not result in increased variability.  We think that matching a self-generated rhythm may facilitate rhythmicity more than matching an external cue.  Future work should explore use of faster cueing rates and use of mental rather than overt singing, in addition to determining the utility of singing during walking in everyday, real-world situations. If singing continues to hold promise in future studies, this could represent a substantial advance as singing is universally available, inexpensive, and adaptable.

     

     

    Copyright

    The ISPGR blog applies Creative Commons Attribution (CC BY) license to figure and text of the article.

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

     

    Publication

    Harrison, E. C., McNeely, M. E., & Earhart, G. M. (2017). The feasibility of singing to improve gait in Parkinson disease. Gait & Posture53, 224-229.

    https://www.ncbi.nlm.nih.gov/pubmed/28226309

     

    The authors

    Gammon M. Earhart, PT, PhD, Program in Physical Therapy, Washington University in St. Louis

    Dr. Earhart is Professor and Director of the Program in Physical Therapy at Washington University in St. Louis.  Her research focuses on the neural control of movement in health and disease, with an emphasis on postural and locomotor control in Parkinson disease.   

     

    Elinor C.  Harrison, BA, Program in Physical Therapy, Washington University in St. Louis

    Elinor Harrison is a professional performance artist turned graduate student.  She is working toward completion of a PhD in Movement Science.  Her dissertation focuses on the use of singing as a means to facilitate movement in people with Parkinson disease.

     

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  • 09 Jun 2017 by Patrick Sparto

    Concussion results in a wide variety of impairments such as cognitive deficits in memory, reaction time and processing speed. Moreover, post-concussion dizziness and balance impairments are found to be common and predictive of worse recovery times.  Therefore, an increasing number of patients with concussion are referred for vestibular physical therapy.
    Although it is likely that cognitive and vestibular impairments after concussion are related, they have only been examined in isolation. This study examined the relationship between cognitive performance and various gait and balance measures in patients referred for vestibular physical therapy after concussion.

    Our study investigated the relationship between gait and balance performance with cognitive performance in a group of 60 adolescents referred for vestibular therapy after concussion. We tested our participants on a range of functional gait and balance measures, such as the Functional Gait Assessment, Timed “UP & GO”, and Five Times Sit to Stand. Our results suggest that, after concussion, both memory deficits and impaired gait and balance can occur in individuals. Our results further show that they are associated with each other. First, we demonstrated that functional balance and gait measures were associated with worse verbal and visual memory on the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). For example, in the figure below, we observed that better performance in visual memory (i.e. higher scores) and verbal memory was related to better performance in the Five Times Sit to Stand (i.e. less time). We also found that higher scores on the Post-Concussion Symptom Scale were associated with lower scores on the Activities-specific Balance Confidence scale and higher scores on the Dizziness Handicap Inventory.

    Spatial navigation is frequently affected after concussion and is important for both gait and balance tasks as well as memory tasks. Clinicians working with patients after concussion should check whether any observed cognitive impairments might be partially attributed to declines in spatial navigation rather than an isolated memory decline. Vestibular therapists should consider giving dual-task exercises, combining balance and cognition, during the rehabilitation process to reduce the impact of cognitive performance on gait and balance function. It will be interesting to see in future studies whether the associations between cognitive and balance affect recovery trajectories after concussion.
     

    Figure: Association between Five Times Sit to Stand Performance and Visual and Verbal Memory performance in 60 adolescents with a concussion who were referred for vestibular physical therapy. Higher visual and verbal memory scores were related to better performance on the Five Times Sit to Stand.


    Publication
    Alsalaheen BA, Whitney SL, Marchetti GF, Furman GM, Kontos AP, Collins MW, Sparto PJ:  Relationship between cognitive assessment and balance measures in adolescents treated with vestibular physical therapy after concussion. Clin J Sport Med. 2016. 26(1):46-52. PMCID:  PMC4856020

    http://journals.lww.com/cjsportsmed/Citation/2016/01000/Relationship_Between_Cognitive_Assessment_and.7.aspx

    The authors

    Bara Alsalaheen, PT, PhD is an Assistant Professor of Physical Therapy at University of Michigan-Flint, Michigan, USA. His research focuses on understanding factors associated with variations in concussion risks, recovery times and rehabilitation outcomes. This research was completed when Dr. Alsalaheen was a doctoral student at Dr. Sparto’s laboratory at University of Pittsburgh.


    Patrick Sparto, PT, PhD is an Associate Professor of Physical Therapy at the University of Pittsburgh. His research interests include the neuroimaging of postural control, the biomechanics of step initiation, and balance impairments after concussion.

     

     

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  • 30 May 2017 by Takeshi Yamaguchi

    Preventing falls is one of the major challenges of our ISPGR community. As part of addressing this challenge, the dynamic postural stability of human gait has been attracting attention from many researchers. When slippery or uneven surfaces cause a large balance perturbation during gait, such as a slip or trip, current postural stability measures indicate whether postural stability is maintained. They do not, however, indicate the degree of instability. In this study, we introduced a desired center of pressure (dCOP) to assess the degree of dynamic postural instability. The dCOP is defined as a virtual point on the ground where the moment around the body center of mass (COM) becomes zero, which occurs when the dCOP and the measured COP (mCOP) coincide. We hypothesized that, when the misalignment of the dCOP and mCOP (dCOP-mCOP) increases to a certain value due to a large perturbation, it becomes difficult to take the reactive step necessary to recover balance and continue walking. The objective of this study was to test this hypothesis in healthy participants during an induced slip while turning.

    Twelve healthy young adult males participated and were asked to: 1) walk straight and turn 60 degrees to the right with the right foot (spin turn) on a dry surface, and 2) walk straight and perform a 60-degree spin turn to the right on a slippery surface. The dCOP-mCOP during turning in the slip trials was significantly larger in trials where a fall occurred compared to the no-slip trials and slip trials where balance was maintained. This was particularly the case in x-direction (i.e., the medial-lateral direction during forward gait). The receiver operating characteristic (ROC) analysis indicated that the dCOP-mCOP in the x-direction was a good indicator of fall risk due to a slip during turning (area under the curve, AUC =0.93). The threshold of dCOP-mCOP in the x-direction for distinguishing trials at risk of a fall from those at no risk of a fall was 0.55 m.

     

    Figure: A) Inverted pendulum model and the desired center of pressure (dCOP) in the sagittal plane. B) Experimental set-up and movement instruction: 1) straight walk and 60-degree spin turn on the dummy sheet, and 2) straight walk and 60-degree spin turn on the slippery sheet. C) Relative location of dCOP with respect to mCOP for spin turn trials. The origin corresponds to the location of mCOP, and each plot indicates the dCOP location relative to the mCOP at which the dCOP–mCOP took the largest value in each trial.

     

    Our study shows that participants were not able to recover walking by taking a successful reactive step after slipping when the dCOP-mCOP reached a certain value, particularly in the x-direction. Furthermore, we were able to differentiate between successful and unsuccessful recoveries using our dCOP-mCOP concept. These results indicate the feasibility of our dCOP concept in assessing the risk of fall due to an induced slip during turning. The misalignment of dCOP and mCOP may provide insight into the variability of gait parameters such as the step length and width of older adults or patients with movement disorders. The dCOP could also yield insight into the desired foot placement for stable gait and contribute to the development of fall prevention interventions.

     

    Publication

    Yamaguchi T, Higuchi H, Onodera H, Hokkirigawa K, Masani K. (2016) Misalignment of the Desired and Measured Center of Pressure Describes Falls Caused by Slip during Turning. PLOS ONE 11: e0155418.  https://doi.org/10.1371/journal.pone.0155418

     

    The author

    Takeshi Yamaguchi

    Associate Professor, Graduate School of Engineering, Graduate School of Biomedical Engineering, Tohoku University, Japan

    Takeshi Yamaguchi is an associate professor at the graduate school of engineering and graduate school of biomedical engineering, Tohoku University. His primary research interests involve the tribology of the shoe and floor interface and biomechanics of gait with the goal of finding ways to reduce slips and fall accidents.

     

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  • 19 May 2017 by Lis Boulton

    Balance, strength and physical activity are important factors for healthy ageing and preventing age-related functional decline. In order to be effective, preventive interventions must target risk factors for functional decline, be tailored to the needs and preferences of the individual, and be designed to change behaviour to a sustained healthier lifestyle. Smartphones and smartwatches are used by an increasing number of people, with thousands of smartphone applications available to promote healthy lifestyles. However, few of these applications are evidence based, meaning that their contribution to overcoming the challenges presented by an ageing population is limited.

    The European Project ‘PreventIT’ (EU Horizon 2020 Grant Agreement No. 689238) aims to address this issue, by developing an evidence-based mHealth behaviour change intervention. PreventIT has adapted the Lifestyle-integrated Functional Exercise (LiFE) programme, which reduced falls in people 75 years and over (BMJ 2012; 345:e4547), for a younger cohort (aLiFE). The aLiFE programme incorporates challenging strength and balance/agility tasks, as well as specific recommendations for increasing physical activity in young-older adults, aged 60-70 years. Personalised advice is given on how to integrate strength, balance and physical activities into existing daily routines. aLiFE was then operationalised to be delivered using smartphones and smartwatches (eLiFE), providing the opportunity to send timely motivational messages and real-time feedback to the user. Both aLiFE and eLiFE are behaviour change interventions, supporting older adults to form long term physical activity habits. PreventIT has taken the original LiFE concept and further developed the behaviour change elements, explicitly relating and mapping them to Social Cognitive Theory and behaviour change techniques. Goal setting, planning, prompts and real-time feedback are used to deliver a person-centred experience for participants in the intervention. Findings from the aLiFE and eLiFE pilot studies highlighted the feasibility and acceptability of the PreventIT motivational strategy, with the vast majority of the participants rating the programmes positively (satisfaction score median: 6 points, out of maximum 7).

    Mobile technology such as smartphones and smartwatches can be used effectively to monitor behaviour and to deliver a personalised intervention. The PreventIT mHealth intervention focusses on behaviour change from initiation to long-term maintenance, addressing the different phases of adopting a healthier lifestyle. As such, it makes a strong contribution to the developing field of evidence-based mHealth. The interventions (aLiFE and eLiFE) are currently being trialled in a three-site, three-arm feasibility randomised controlled trial in Norway, the Netherlands and Germany. An overview of the project can been viewed on YouTube: https://www.youtube.com/watch?v=upAfGHbNvdU

     

     

     

     

     

     

     

    Publication:

    Helbostad JL, Vereijken B, Becker C, Todd C, Taraldsen K, Pijnappels M, Aminian K, Mellone S. Mobile Health Applications to Promote Active and Healthy Ageing. Sensors. 2017; 17(3):622. http://www.mdpi.com/1424-8220/17/3/622

    Author:

    Dr Lis Boulton is a Research Associate in the School of Health Sciences at the University of Manchester, UK, and is a member of the EU-PreventIT consortium. Her research focusses on the use of technologies to facilitate behavioural change, to encourage older adults to be more physically active. Lis works with Professor Chris Todd in developing and operationalising the motivational strategy for PreventIT. (elisabeth.boulton@manchester.ac.uk)

     

     

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  • 08 May 2017 by Ruopeng Sun

    During daily life, locomotion tasks are often accompanied by a concurrent task such as talking, texting or recalling a shopping list. There is a wide body of empirical evidence on the profound negative effects of concurrent cognitive challenges on gait, the cognitive task itself, and other clinical outcomes such as falls. Such reductions in performance are commonly interpreted as competition for attentional resources between the postural and cognitive task. Various cognitive tasks have been utilized in dual-task research, such as backwards counting, reaction time, memory recall, Stroop and verbal fluency tasks. Performance for these tasks is traditionally measured through the rate of error or the response time. However, such descriptive measures lack the temporal resolution to track the dynamics of attention allocation during postural control. Hence, we aimed to evaluate the timing of postural prioritization during stepping using a continuous finger-tapping task.

    Ten healthy young adults with a mean age of 21 years participated in this study. Participants were asked to perform a rapid voluntary step with either their left or right foot after hearing an auditory tone (simple/choice reaction paradigm), while also tapping their right index finger continuously on a handhold numeric keypad (Figure A). Three variants of concurrent attentional tasks were used: (1) single task: holding keypad only, no finger-tapping; (2) low attention-demanding: one-button tapping task; (3) high attention-demanding: four-button tapping task. We performed wavelet analysis on the stimulus-locked finger-tapping data to determine the temporal change of tapping frequency related to reactive stepping (Figure B). Results showed that the postural performance was negatively affected only by the high attention-demanding task. Significant reduction of post-stimulus tapping speed was observed across all test conditions, indicating attention shift during the execution of a step. In addition, the high attention-demanding task induced early postural prioritization during the choice reaction stepping condition when different motor programs needed to be prepared and executed.

    Our study shows that a continuous finger-tapping task can be used to track attention allocation during step initiation, by detecting the reduction of tapping speed in response to the stimulus presentation. The results suggest that the postural task is prioritized during step planning and execution, especially when the motor program cannot be pre-selected in case of the choice reaction condition. Our novel method can be used to probe when and how attention shifts during other locomotion tasks, as well as track attention allocation in various aging and pathological populations.

    Publication

    Sun, R, & Shea, J. B. (2016). Probing attention prioritization during dual-task step initiation: a novel method. Experimental brain research234(4), 1047-1056. https://link.springer.com/article/10.1007/s00221-015-4534-z

    The Author

    Ruopeng (Robin) Sun, Ph.D. Motor Control Research Lab, Department of Kinesiology and Community Health, University of Illinois Urbana-Champaign

    Ruopeng (Robin) Sun received his Ph.D. in kinesiology from Indiana University Bloomington and currently works as a Postdoctoral Research Associate in the Motor Control Research Lab at University of Illinois Urbana-Champaign (http://publish.illinois.edu/motorcontrol). His research interests are: novel technology in fall risk assessment, gait adaptability in complex locomotion task, and cognitive-motor interference in daily locomotion. 

     

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  • 18 Apr 2017 by Nick Kluft

    Moving safely through the environment requires adequate perception of our abilities in relation to the task at hand. If we have the ability to overcome the biomechanical task demands, execution of the planned task is most likely successful. Knowledge of our own ability is therefore crucial in motor planning. Yet, are we still capable of accurately judging our abilities when we grow older and face the concomitant physical and cognitive declines? Inaccurate judgment of our own ability could either lead to overestimation (e.g., excessive risk taking) or underestimation (e.g., activity avoidance). How can we directly quantify the amount of over-and underestimation in gait? We aimed to quantify the degree of misjudgment between the perceived and actual gait ability in older adults.

    We investigated two paradigms to determine the degree of misjudgment: one used a path width manipulation and the other used a speed manipulation (Figure 1a). We asked 27 older adults to walk within paths of different widths projected on a treadmill. We quantified the actual ability by evaluating the participant’s stepping accuracy on a range of path widths and treadmill speeds. Prior to this actual ability measurement, we asked the participants to indicate the smallest path and highest treadmill speed at which they believed they could still walk within the boundaries of the path to unravel their perceived ability. By doing so, we were able to define the degree of misjudgment as the difference between one’s perceived and actual ability (Figure 1b).

     

    Figure 1: Experimental setup and results

    Our results show that stepping accuracy increased when we broadened the path width, while the stepping accuracy did not decrease when treadmill speed increased (i.e., it was not more challenging to walk on a path at a higher speed). Because stepping accuracy was not affected by treadmill speed but was affected by path width, the latter manipulation was used to determine the degree of misjudgment. In agreement with other studies, we showed disparities between perceived ability and actual ability for some of the participants. Altogether, we directly quantified older adults’ misjudgment of gait ability using a path width paradigm. Such quantification of over-and underestimation of gait abilities in older adults could be beneficial in fall-risk assessment and allow for more tailored interventions.

     

    Publication

    Kluft N, van Dieën JH, Pijnappels M (2017). The degree of misjudgment between perceived and actual gait ability in older adults. Gait & Posture, 51, 275-280. doi: 10.1016/j.gaitpost.2016.10.019

     

    About the author

    Nick Kluft is a PhD candidate at the Department of Human Movement Sciences of the Vrije Universiteit Amsterdam in The Netherlands. His research focuses on the discrepancy between perceived and actual physical ability, and how this misjudgment affects gait, stepping behaviour and responses to gait perturbations in older adults. This research was supported by the Dutch Organisation for Scientific Research (NWO). 

     

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  • 19 Apr 2017 by John Stins

    Humans have the ability to mentally visualize all sorts of objects, events or scenes. This is known as mental imagery. For example, I can generate a vivid experience of swimming in a pool: I ‘feel’ the water flow, I ‘sense’ the temperature, and I ‘move’ my arms and legs. Research has shown that mental imagery (especially of motor acts) is accompanied by changes in bodily states, such as heart rate, muscle tension, and respiration, often in a highly specific manner. Mental imagery also affects postural control, as evidenced by analysis of the center-of-pressure (COP) trajectory as a function of mental content. We performed an experiment inspired by a study by Miles et al. (2010). They found that mental imagery of the (own) future and past induced COP changes. Thinking of the past caused backward displacement of the  COP, whereas thinking of the future caused forward displacement. The authors concluded that the direction of subjective time is represented along a spatial dimension, which in turn led to directional changes in body posture (unintentional ‘leaning’). We performed a conceptual replication and extension of this study, in order to test how general and robust the effect of ‘mental time travel’ is.

     

    Thirty-two participants stood upright and imagined various scenarios that were read aloud. Scenarios described a typical day in the past or in the future; 4 days or 4 years. In addition, some scenarios were pleasant (e.g., receiving a diploma) or unpleasant (being at a funeral). We analyzed postural displacements in the anterior-posterior direction, as a function of the mental content. An important finding was that there was no statistically significant difference between past and future imagery (see Figure). Also, no postural effects of emotion were found. This apparent null finding (all F’s < 1) received support from Bayesian statistics, which quantifies the relative predictive success of the null hypothesis relative to the alternative hypothesis. This Bayesian analysis revealed that the null hypothesis (i.e., no difference between past and future imagery) was 4.8 more likely than the alternative, which is typically considered ‘substantial’ evidence.

     

    Figure 1. Grand averaged wave forms of the COP trace (bold line), plus straight line fit (red line) for past (left panel) and future (right panel) mental imagery. There was no statistical difference between these two conditions.

     

    We have no explanation for why our results diverged from Miles et al. (2010). It could be due to subtle unidentified methodological differences. Alternatively, it could be that the effect is not robust and that posture is insensitive to abstract thought, such as mental time travel.

     

    Publication

    Stins JF, Habets L, Jongeling W, Cañal-Bruland R. (2016). Being (un)moved by mental time travel. Consciousness and Cognition; 42: 374–81. http://www.sciencedirect.com/science/article/pii/S1053810016300666

     

    The author

    Dr. Stins is assistant professor at the Department of Human Movement Sciences, VU University Amsterdam. His research focuses on the interface of experimental psychology (especially cognition and emotion) and motor control, with an emphasis on the control of posture and gait.

     

     

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  • 18 Apr 2017 by Anna Hatton

    Following anterior cruciate ligament (ACL) rupture, reconstructive surgery (ALCR) is often performed to mechanically stabilise the knee, however functional and neuromuscular deficits can persist long after surgery. Impaired single-limb balance control when standing on the ACLR limb compared to healthy individuals has been reported by other groups. Building on these findings, the current study aimed to generate new knowledge as to whether similar balance deficits exist between injured and contralateral uninjured limbs, one year post-surgery, which is typically the time when patients are permitted to return to sport. Uncovering balance deficits in patients who have undergone ACLR is clinically important information, which may help to identify a risk factor with the capacity to predict ACL re-rupture or contralateral injury, and advance rehabilitation strategies post-surgery.

    Our study investigated 100 adults who had undergone a primary hamstring-tendon ACLR in the 12 months prior to testing. Participants performed challenging tasks of static single-limb balance, with eyes closed, whilst standing on the ACLR and uninjured limb. Traditional measures of centre of pressure movement (excursion, velocity) in anterior-posterior and mediolateral directions were collected over 20 seconds, using a Nintendo Wii Balance Board (Figure 1). We were also interested in exploring possible associations between patients who presented with concomitant injury (chondral lesions) or underwent ‘additional’ surgeries (meniscectomy) at the time of ACLR, and balance ability, one year following reconstruction. We found that single-limb standing balance did not differ between the ACLR and uninjured limb for any of the centre of pressure measures of interest (all P values >0.686). Whilst 71 participants were reported to have concomitant injury/surgeries, these factors were not associated with measures of balance ability (all P values >0.213). 

    Findings reported in our article extend, and concur with, prior evidence indicating the absence of balance deficits between the injured and uninjured limbs during less challenging unilateral balance tasks, where visual information was available (i.e. quiet standing with eyes open). However, in the context of wider evidence, which demonstrates that patients who have undergone ACLR show poorer balance control relative to their healthy counterparts, our results point to the suggestion that bilateral balance deficits may exist in this clinical population. For health professionals involved in the management of patients following ACL injury and ACLR, our research implies that clinical assessments of balance, and interventions designed to enhance balance ability, should consider both the injured and uninjured limbs, within the early stages of post-ACLR rehabilitation strategies.

    Figure 1: Standing balance test procedures and Nintendo Wii output (centre of pressure movement)

     

    Publication

    Hatton AL, Crossley KM, Clark RA, Whitehead TS, Morris HG, Culvenor AG. Between-leg differences in challenging single-limb balance performance one year following anterior cruciate ligament reconstruction. Gait & Posture 2017 52:22-25. http://dx.doi.org/10.1016/j.gaitpost.2016.11.013

    The Author

    Dr Anna Hatton is a Lecturer in Physiotherapy and Co-Director of the Centre for Neurorehabilitation, Ageing and Balance Research at The University of Queensland. Her research seeks to explore the sensorimotor control of balance and gait in ageing, neurodegenerative, neuromuscular and musculoskeletal disease populations, to inform the development of novel rehabilitation techniques.

     

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  • 12 Apr 2017 by PAULA POLASTRI

    We regularly move our eyes searching for visual information, and when we do this, postural adjustments are necessary to compensate or facilitate these movements. Previous studies in young adults show that body sway is attenuated during saccadic eye movements and reveal that challenging stances affects this relationship. This suggests that in an attempt to increase visual stability to perform more spatially accurate saccades, people limit their body sway during saccadic eye movements. The eye-posture relationship appears to be affected by the aging. Older adults have slower and less accurate saccadic eye movements and exhibit more sway during postural tasks compared to young adults. These changes in gaze and postural behaviors might be associated to increase of falls in older people. We aimed to investigate the influence of saccadic eye movements on postural control in older adults by manipulating the difficulty level of visual and postural tasks.

     

    Twelve older adults were asked to maintain quiet upright standing during two stance conditions (wide or narrow stance) combined with three gaze conditions (fixation, saccades at 0.5 Hz, or saccades at 1.1 Hz). The target in the gaze conditions was a red circle on a white background, which either stayed in place or jumped horizontally to elicit saccades. We found that the mean amplitude of mediolateral head and trunk sway was higher and sway frequency was lower at narrow compared to wide stance condition. In anteroposterior direction, the mean amplitude of sway was lowest at saccades at 1.1 Hz, followed by saccades at 0.5 Hz, with highest values during the fixation condition, following a linear trend. A similar trend was observed for the frequency of head and trunk sway in mediolateral and anteroposterior direction, participants exhibited highest sway frequency at saccades 1.1 Hz, followed by saccades at 0.5 Hz, with lowest values in the fixation condition.

     

     

    Figure: (A) Summary of the effect of gaze on mean sway amplitude and frequency of the head and trunk in anteroposterior  and mediolateral  directions. (B) Summary of the effect of stance on mean sway amplitude and frequency of the head and trunk in AP and ML directions. Differently of young adults, no statistical significance was observed between wide and narrow stances in anteroposterior direction.

     

    Our results suggest that older adults attenuate their head and trunk sway during horizontal saccadic eye movements, in a similar way as young adults, during the wide stance condition. However, unlike young adults, older adults did not attenuate their sway during the more challenging narrow stance condition. This suggests a more rigid postural control strategy in older adults to maintain the postural stability during the performance of visual tasks. Further studies are required to track the way of older adults move their eyes in search of visual information during daily activities and how this affects the postural stability, particularly during challenging stance conditions.

     

    Publication

    Aguiar SA, Polastri PF, Godoi D, Moraes R, Barela JA, Rodrigues ST. (2015). Effects of saccadic eye movements on postural control in older adults. Psychology & Neuroscience, 8:1, 19-27.

    http://psycnet.apa.org/?&fa=main.doiLanding&doi=10.1037/h0100352

     

    The author

    Paula F. Polastri – Assistant Professor of São Paulo State University (UNESP), Faculty of Science - Department of Physical Education, Bauru – Brazil. 

    Paula F. Polastri is coordinator of the Laboratory of Information, Vision and Action (LIVIA) together with Sergio T. Rodrigues. Currently, their research focuses on understanding the relationship between gaze and postural control. Their further study interests are to investigate how the changes in the eye-posture relationship affect the coupling between sensory information and body sway.

     

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  • 19 Mar 2017 by Milou Coppens

    Assessment of free-living gait is becoming increasingly popular in mobility and fall-risk research because of its ecological validity and advances in sensor technology. However, an essential step herein is detecting when someone is walking, which is not as easy as it seems. Previous studies have reported boundaries in separating gait from other activities as shuffling and standing still. Furthermore, inaccurate and instable placement of a sensor were described as difficulties for proper gait detection, even though these factors are hard to avoid when older adults wear sensors without supervision. Therefore, we set up a study to develop an algorithm for reliable gait detection from inertial sensors without the need for rigid sensor placement.

     

    Fifty-one older adults with an average age of 83 years wore the Philips Senior Mobility Monitor, containing a triaxial accelerometer and a barometer, on a lanyard around their neck. We randomly placed the device underneath or outside clothing and changed the length of the lanyard between participants to mimic real-life variations. While being filmed, participants walked in a semi-controlled environment and performed free-living activities such as climbing stairs and sit-to-stand transfers. We annotated bouts of level-ground gait (excluding shuffling) in the videos as gold standard. To differentiate gait from other activities, we developed a wavelet-based decision tree algorithm.  Data of half of the participants was used to optimize algorithm thresholds (e.g. minimal number of heel strikes), while data of the other half of the participants was kept for validation. Subsequently, the algorithm was used to detect walking episodes in the sensor data of the validation group, which strongly corresponded to those annotated in the videos with high accuracy (≥97%) and low false-positive errors (≤1.9%) (Fig. 1).

     

    To identify whether gait parameters from free-living gait were related to standardized laboratory-assessed gait parameters, we calculated the median and maximum cadence from the inertial sensor data and compared those with cadence obtained from three walks on a 10-m GaitRite walkway. We found that median and maximum cadence were strongly correlated with cadence measured on the GaitRite. Despite this strong correlation, median cadence was significantly lower in free-living gait compared to cadence measured on the GaitRite.

     

    Our novel wavelet-based method is feasible for detecting free-living gaits from a pendant-worn inertial sensor. Giving the fact that the exact location of the sensor differed between participants and could even change during the experiment, this method is promising to detect gait in the home environment. As laboratory gait parameters where related to, but more equal to someone’s ‘best’ free-living gait parameters, home assessments have the potential to provide additional information for investigating daily performance.

     

    Publication

    Brodie MAD, Coppens MJM, Lord SR, Lovell NH, Gschwind YJ, Redmond SJ, Del Rosario M, Wang K, Sturnieks DL, Persiani M, Delbaere K. (2016). Wearable pendant device monitoring using new wavelet-based methods shows daily life and laboratory gaits are different. Med Biol Eng Comput 54: 663. doi:10.1007/s11517-015-1357-9 https://link.springer.com/article/10.1007/s11517-015-1357-9

     

    The author

    Milou Coppens is a PhD Candidate at the Radboud University Medical Center in Nijmegen, The Netherlands.

     

    Milou is highly interested in using novel techniques to understand the mechanisms underpinning balance problems due to ageing and disease. Currently, she is using non-invasive brain stimulation and brain imaging techniques to investigate the neural control of postural balance and how this might be altered after brain damage.

     

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  • 13 Mar 2017 by Tanvi Bhatt

    With the evolution of bipedal posture humans are not immune to falls. Falls are a significant societal burden, being a leading cause of morbidity and mortality, especially in people aging with disabilities such as stroke. A fall after encountering a large external disturbance to the body, such as a slip or a trip, can be effectively prevented via successful protective (reactive) self-defence strategies. Such strategies include grasping and stepping, and essential re-establish the relationship between the body and the base of support, which could be displaced based on the direction of the disturbance. While earlier it was thought that such protective postural responses were primarily automatic, and initiated and controlled reflexively within the spinal cord, emerging evidence indicates that the brain has an important role to play in modulating these responses. In the healthy nervous system, this modulation can be seen in the form of rapidly and appropriately adjusting and adapting the protective response based on the perceived threat (e.g. adjusting step length based on the magnitude of the disturbance). Our study examined if age-related structural (mainly degenerative) changes in the brain would impacted this modulation, and if the magnitude of this impact would be enhanced when an additional brain injury, such as stroke, co-existed with normal aging.

     

    Young healthy adults, older healthy adults, and chronic stroke survivors were exposed to slip-like perturbations while they were standing on a motorized instrumented treadmill. The perturbations induced a balance loss much like what you would experience while standing on a bus that started to move suddenly from a standstill. Participants were tested on three levels of difficulty, which consisted of increasing acceleration levels of the treadmill belt. All subjects resorted to taking a protective step to restore their balance, even at the lowest level of belt acceleration. There were no falls in the young and the healthy older adults, but the number of falls increased with increasing acceleration level in the stroke participants. The number of steps taken to restore balance increased with increasing difficulty levels in all groups. The young subjects were able to increase control of their center of mass (COM) stability with increasing acceleration levels. This was achieved by increasing the length of their protective step (spatial parameter) along with decreasing their step velocity (temporal parameter), rather than altering the control of their trunk (upper body) movement. While older adults were able to alter their responses with an increase in stability between the lower difficulty levels, they could not scale their spatial and temporal stepping response to the highest level of acceleration. Stroke participants on the other hand could not modulate COM stability, step length, or step velocity with increasing difficulty levels, which could explain the highest number of falls in this population.

     

    An accurate sensory perception of the perturbation (in terms of displacement and velocity) is required to generate a timed and graded response to initiate and execute an appropriate body response. Our results demonstrate a partially preserved ability to efficiently respond to challenging environmental threats by modulating the reactive balance response in older adults, which breaks down as the magnitude of threat increases. Such modulatory ability is significantly impaired in people aging with stroke, which could be one of the factors explaining the 3-fold increase in fall risk in this population compared to their healthy counterparts. Results from this study suggest that reactive balance assessment measures could miss detecting community-dwelling older adults at risk of falls if these tests at conducted at lower “threat” levels. Furthermore, our results suggest that fall prevention paradigms for people aging with and without neurological disorders, such as stroke should, should include reactive balance training at progressively increasing levels of perturbation threat to entrain modulation of protective stepping responses.

    Figure A. Experimental set-up for delivering perturbations in standing position, wherein participants executed a natural response to recover balance upon receiving a sudden slip-like perturbation. B.  The perturbation outcome for each group showing the proportion of falls and recoveries (no falls) at all three perturbation levels. The older stroke survivors showed significantly higher incidence of falls on level III perturbation compared with levels I & II (p < 0.01). At the highest perturbation intensity (level III), the stroke group also had more falls compared with the young and older adults (p < 0.01). C. The percentage of multiple stepping response at each perturbation intensity. Unlike young adults, for older adults and stroke survivors the proportion of multiple stepping responses on perturbation levels II and III than at level I, * p < 0.01. Both older adults and older stroke survivors showed higher proportion of multiple steps compared with younger adults # p < 0.01. 

     

    Publication

    Patel P.J., Bhatt T. Does aging with a cortical lesion increase fall-risk: Examining effect of age versus stroke on intensity modulation of reactive balance responses from slip-like perturbations. Neuroscience 2016 Oct 1;333:252-63. http://dx.doi.org/10.1016/j.neuroscience.2016.06.044

     

    Authors

    Tanvi Bhatt, PT, PhD, Department of Physical Therapy, University of Illinois at Chicago

    Dr. Bhatt is an assistant professor in the department of physical therapy and leads the Cognitive, Motor & Balance Rehabilitation (CogMoBal) Laboratory. Her research involves investigating the neuromechanical basis of balance recovery from external perturbations such as slips and trips, and subsequently designing intervention paradigms for reducing fall-risk in healthy and pathological populations. Her research interest and focus also lays in examining effects of alternative cognitive and motor therapies for improving impairment, function, and community participation in community-dwelling people with neurological disorders.

     

    Prakruti Patel, PT, MS, PhD, Department of Physical Therapy, University of Illinois at Chicago

    Prakruti Patel is a graduate student in Dr. Bhatt’s lab. Prakruti will graduate with her doctoral degree in Rehabilitation Sciences in Spring 2017. Her dissertation focussed on examining cognitive-motor interference in for locomotor-balance tasks in people with aging and stroke.

     

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  • 02 Mar 2017 by Takahiro Higuchi

    Stroke survivors often suffer from motor paralysis on one side of the body. It can be challenging for them to walk through narrow openings, such as doorways or space created by pedestrians. This is because, while body rotation with a pivot-like turn is necessary to fit through apertures without contact, performing such a turn using the paretic limb is difficult. Therefore, we investigated how they could successfully avoid obstacles and fit through apertures in spite of their motor paralysis. 

    Participants included 10 stroke fallers, 13 stroke non-fallers, and 23 controls. A door-like aperture was created as a space between two projector screens (Fig. 1a). Participants were asked to approach and cross the aperture without contacting the screen. In some trials, the aperture was so narrow that body rotation was necessary to avoid contacting the screen. Our results showed that stroke fallers contacted the screens more frequently than any of the other participants. This suggests that the inability to safely cross an aperture is related to the risk of falling. As expected, stroke fallers contacted the screen mainly on their paretic side. Interestingly, enough, these contacts were less frequent when they tried to navigate the opening starting with their paretic side (Fig. 1b). Three-dimensional motion analyses showed that stroke participants rotated their bodies in multiple steps (rather than with pivot-like turns), possibly to deal with their motor paralysis. 

    Our results suggest that, although stroke fallers have difficulty avoiding contact with obstacles on their paretic side, adopting a strategy to fit through an opening from their paretic side can help them avoid contacts. We have two explanations as to why such a strategy helped improve their behavior; it could be that vision of the paretic side helped guiding the movement or that spatial attention was directed to the location of the paretic side of the body. We are now investigating whether such a strategy would be a helpful intervention to help stroke patients pass narrow openings safely. 

    Figure 1(a)

     

     

    Figure 1(b)

     

    Figure 1(a) Participants were asked to walk through a narrow opening created by two projector screens. Our focus was on how successfully they avoided contacts with the screen and how they approached and crossed a narrow opening while dealing with their motor paralysis. (b) Contact frequency classified according to the body side where contact occurred.

     

    Publication
    Muroi D, Hiroi Y, Koshiba T, Suzuki Y, Kawaki M, Higuchi T. (2017) Walking through apertures in individuals with stroke. PLOS ONE 12: e0170119. 

    http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0170119
     

    The author
    Takahiro Higuchi (Ph.D.)
    Professor, Department of Health Promotion Science, Tokyo Metropolitan University

    Takahiro Higuchi earned a Ph.D. in Psychology from Tohoku University in Japan. He gained additional research experience during his postdoctoral fellowship with Dr. Aftab E. Patla at the University of Waterloo in Canada from 2004 to 2006. He is primarily interested in the visuomotor control of adaptive locomotor

     

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  • 07 Mar 2017 by Hiroko Tanabe

    How do we maintain balance? What is our control strategy during upright standing? These questions are not as easy as they look. Even when standing quietly, we need to activate various muscles in order to not collapse under the influence of gravity. This is made extra difficult by the frequent balance disturbances we experience in daily life, for instance due to neuromuscular noise or people bumping into us. The postural control mechanism must hence be stable, but also adaptive to internal and external disturbances (this adaptability is called postural robustness). Postural control is conventionally thought to continuously actuate the body segments based on joint state; however, this strategy cannot bring forth the bimodal distribution of ankle movements that are commonly observed during standing. Therefore, we hypothesized that balance during quiet standing is controlled intermitted, not continuous. In this study, we demonstrated the relevance of a new concept for postural control called intermittent feedback control, in which each joint is actively actuated only when the instability of the system exceeds a certain threshold.  

    We used a quadruple inverted pendulum as a model for tiptoe standing to simulate upright posture with internal disturbance accompanied by the change in posture and sensory feedback. The four segments represented the foot, shank, thigh, and head-arm-trunk segments and had human anthropometric characteristics. Each joint was actuated by an anti-gravitational joint torque generated according to three different control strategies: 1) continuous control (a continuous active and passive joint torque based on joint angle and velocity), 2) intermittent control (an intermittent active joint torque only when instability of the system increases and an continuous passive torque), and 3) passive control (only a passive torque from musculotendinous viscoelasticity). Our results show that only when the hip is controlled intermittently, we obtain joint oscillations with amplitudes and variations that are similar to those during actual human standing. Also, there were substantial differences in postural robustness among different joint control strategies.

    Figure: a visualization of our model for intermitted postural control

    Our results highlight the advantages of intermittency for the postural control system and could have far-reaching implications for training and rehabilitation. For example, based on the concept of intermittent control, we might be able to train the system to be robust to internal and external perturbations of a certain intensity. Furthermore, our findings may provide important insight into a long-lasting debate: is lower variability indeed more stable? In conclusion, our findings suggested that human upright posture could be controlled intermittently and that this intermittent feedback control may be associated with increased postural robustness.

     

    Publication

    Tanabe H, Fujii K, Suzuki Y, Kouzaki M (2016). Effect of intermittent feedback control on robustness of human-like postural control system. Scientific Reports 6, 22446. doi: 10.1038/srep22446. http://www.nature.com/articles/srep22446

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    The author

    Hiroko Tanabe, Ph.D.

    Hiroko Tanabe is an assistant professor at the Graduate School of Arts and Sciences, The University of Tokyo, Japan. Her research interests are the motor control mechanism in patients and athletes. She is currently working on neural-muscular-skeletal quantification of psychiatric patients, postural adaptation during pitching motion of baseball players, and aesthetic walking motion and its control theory of dancers.

     

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  • 19 Feb 2017 by Toby Ellmers

    During walking, we rely on visual information to identify tripping hazards and navigate safely through the environment. The way we shift our gaze and scan the environment (our visual-search behaviour) is affected by ageing and fall risk. Older adults at high-risk of falling will transfer their gaze away from a stepping target before the step has been completed (i.e., prior to heel contact); a behaviour which is causally linked to reduced stepping accuracy. Moreover, when navigating a series of stepping constraints, high-risk older adults will adopt a less-variable pattern of visual-search, whereby their gaze is fixated predominately on the initial stepping target, at the expense of upcoming obstacles or targets. We hypothesised that this maladaptive and less-variable pattern of visual-search behaviour may be caused by inefficiencies in attentional processing, with high-risk older adults possessing insufficient cognitive resources to generate and store a ‘spatial map’ of their environment. Insufficient cognitive resources for attentional processing during walking may be due to psychological factors. When anxious or following injury or accident (e.g., falls), individuals may attempt to consciously monitor and control movements, which are usually considered largely ‘automatic’. This phenomenon is frequently described as ‘reinvestment’. It is believed that cognitive resources are required to consciously attend to the process of walking, which would limit the resources available for other processes, such as proactively scanning one’s environment. Yet, little is known about how either cognitive load or reinvestment influence visual-search behaviour during walking.

    Younger adults traversed a non-linear path (containing two precision stepping targets) while performing a secondary serial-subtraction task and wearing a gaze-tracker unit. Outcome measures included gaze behaviour, stepping accuracy, and time to complete the walking task. When walking while simultaneously carrying out the serial-subtraction task, participants visually fixated on task-irrelevant areas ‘outside’ the walking path more often and for longer durations, and fixated on task-relevant areas ‘inside’ the walkway for shorter durations. These changes were most pronounced in high-trait-reinvesters. The increased task-irrelevant ‘outside’ fixations were accompanied by slower walking times and greater gross stepping errors. Interestingly, these ‘outside’ fixations were temporally related to the performance of the dual-task, with participants more likely to look away from the walkway (or, ‘gaze into thin air’) in the 330ms directly preceding the verbalisation of the dual-task calculation.

    Our findings suggest that attention is important for the maintenance of effective gaze behaviours, supporting previous claims that maladaptive changes in visual-search observed in high-risk older adults may be a consequence of inefficiencies within attentional processing. As these changes were most pronounced in high-trait-reinvesters, we speculate that reinvestment-related processes placed additional cognitive demands upon working memory.

     

     

    Figure. A: An example of a task-relevant ‘inside’ fixation, whereby the participant fixates on an area within their walking path. B: An example of a task-irrelevant ‘outside’ fixation, whereby the participant fixates on an area outside of their walking path. C: Duration (as a percentage of overall fixation durations) of task-relevant ‘inside’ and task-irrelevant ‘outside’ fixations under conditions of Cognitive Load, ** p <.01. D: Number of task-irrelevant ‘outside’ fixations (per second) under conditions of Cognitive Load, * p <.05.

     

    Publication

    Ellmers TJ, Cocks AJ, Doumas M, Williams AM, Young WR (2016) Gazing into Thin Air: The Dual-Task Costs of Movement Planning and Execution during Adaptive Gait. PLoS ONE 11(11): e0166063.

    http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0166063

     

    The Author

    Toby Ellmers. Ph.D. Student. Department of Life Sciences, Brunel University London.

    Toby Ellmers is a Ph.D. Student at the FP² (Falls Prediction and Prevention) Lab at Brunel University, London. His research involves the studying of the psychological mediators of elderly fall-risk and the development of intervention programs grounded in psychological and motor-learning theory.

     

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