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Posts Tagged walking
[Abstract + References] Experimental Human Walking and Virtual Simulation of Rehabilitation on Plane and Inclined Treadmill – Conference paper
The paper presents the results of the authors concerning the experimental human walking and numerical simulation of human rehabilitation on a treadmill. Using Biometrics data acquisition system based on electrogoniometers, experimental measurements for ankle, knee and hip joints of right and left legs during walking on plane and inclined treadmill are performed. The human legs motion assistance for rehabilitation is proposed with an attached exoskeleton. The numerical simulation of a virtual mannequin walking with the attached exoskeleton on a plane and inclined treadmill is performed, using ADAMS virtual environment. A comparison between human experimental measurements and numerical simulations of a virtual mannequin with exoskeleton is presented.
[Abstract] Effects of mirror therapy on walking ability, balance and lower limb motor recovery after stroke: a systematic review and meta-analysis of randomized controlled trials
To investigate the effects of mirror therapy on walking ability, balance and lower limb motor recovery in patients with stroke.
MEDLINE, EMBASE, Web of Science, CENTRAL, PEDro Database, CNKI, VIP, Wan Fang, ClinicalTrials.gov, Current controlled trials and Open Grey were searched for randomized controlled trials that investigated the effects of mirror therapy on lower limb function through January 2018. The primary outcomes included were walking speed, mobility and balance function. Secondary outcomes included lower limb motor recovery, spasticity and range of motion. Quality assessments were performed with the PEDro scale.
A total of 13 studies (n = 572) met the inclusion criteria. A meta-analysis demonstrated a significant effect of mirror therapy on walking speed (mean difference (MD) 0.1 m/s, 95% confidence interval (CI): 0.08 to 0.12, P < 0.00001), balance function (standard mean difference (SMD) 0.66, 95% CI: 0.43 to 0.88, P < 0.00001), lower limb motor recovery (SMD 0.83, 95% CI: 0.62 to 1.05, P < 0.00001) and passive range of motion of ankle dorsiflexion (MD 2.07°, 95% CI: 082 to 3.32, P = 0.001), without improving mobility (SMD 0.43, 95% CI: −0.12 to 0.98, P = 0.12) or spasticity of ankle muscles (MD −0.14, 95% CI: −0.43 to 0.15, P = 0.35).
via Effects of mirror therapy on walking ability, balance and lower limb motor recovery after stroke: a systematic review and meta-analysis of randomized controlled trials – Yi Li, Qingchuan Wei, Wei Gou, Chengqi He, 2018
[Abstract] Effects of an Exercise Protocol for Improving Handgrip Strength and Walking Speed on Cognitive Function in Patients with Chronic Stroke
BACKGROUND: Handgrip strength and walking speed predict and influence cognitive function. We aimed to investigate an exercise protocol for improving handgrip strength and walking speed, applied to patients with chronic stroke who had cognitive function disorder.
MATERIAL AND METHODS: Twenty-nine patients with cognitive function disorder participated in this study, and were randomly divided into one of two groups: exercise group (n=14) and control group (n=15). Both groups underwent conventional physical therapy for 60 minutes per day. Additionally, the exercise group followed an exercise protocol for handgrip using the hand exerciser, power web exerciser, Digi-Flex (15 minutes); and treadmill-based weight loading training on their less-affected leg (15 minutes) using a sandbag for 30 minutes, three times per day, for six weeks. Outcomes, including cognitive function and gait ability, were measured before and after the training.
RESULTS: The Korean version of Montreal Cognitive Assessment (K-MoCA), Stroop test (both simple and interference), Trail Making-B, Timed Up and Go, and 10-Meter Walk tests (p<0.05) yielded improved results for the exercise group compared with the control group. Importantly, the K-MoCA, Timed Up and Go, and 10-Meter Walk test results were significantly different between the two groups (p<0.05).
CONCLUSIONS: The exercise protocol for improving handgrip strength and walking speed had positive effects on cognitive function in patients with chronic stroke.
Link to Full Text Download —> Get your full text copy in PDF | Medical Science Monitor
January 8, 2018
UC San Francisco neurologists have discovered monthly cycles of brain activity linked to seizures in patients with epilepsy. The finding, published online January 8 in Nature Communications, suggests it may soon be possible for clinicians to identify when patients are at highest risk for seizures, allowing patients to plan around these brief but potentially dangerous events.
“One of the most disabling aspects of having epilepsy is the seeming randomness of seizures,” said study senior author Vikram Rao, MD, PhD, an assistant professor of neurology at UCSF and member of the UCSF Weill Institute for Neurosciences. “If your neurologist can’t tell you if your next seizure is a minute from now or a year from now, you live your life in a state of constant uncertainty, like walking on eggshells. The exciting thing here is that we may soon be able to empower patients by letting them know when they are at high risk and when they can worry less.”
Epilepsy is a chronic disease characterized by recurrent seizures — brief storms of electrical activity in the brain that can cause convulsions, hallucinations, or loss of consciousness. Epilepsy researchers around the world have been working for decades to identify patterns of electrical activity in the brain that signal an oncoming seizure, but with limited success. In part, Rao says, this is because technology has limited the field to recording brain activity for days to weeks at most, and in artificial inpatient settings.
At UCSF Rao has pioneered the use of an implanted brain stimulation device that can quickly halt seizures by precisely stimulating a patient’s brain as a seizure begins. This device, called the NeuroPace RNS® System, has also made it possible for Rao’s team to record seizure-related brain activity for many months or even years in patients as they go about their normal lives. Using this data, the researchers have begun to show that seizures are less random than they appear. They have identified patterns of electrical discharges in the brain that they term “brain irritability” that are associated with higher likelihood of having a seizure.
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The new study, based on recordings from the brains of 37 patients fitted with NeuroPace implants, confirmed previous clinical and research observations of daily cycles in patients’ seizure risk, explaining why many patients tend to experience seizures at the same time of day. But the study also revealed that brain irritability rises and falls in much longer cycles lasting weeks or even months, and that seizures are more likely to occur during the rising phase of these longer cycles, just before the peak. The lengths of these long cycles differ from person to person but are highly stable over many years in individual patients, the researchers found.
The researchers show in the paper that when the highest-risk parts of a patient’s daily and long-term cycles of brain irritability overlap, seizures are nearly seven times more likely to occur than when the two cycles are mismatched.
Rao’s team is now using this data to develop a new approach to forecasting patients’ seizure risk, which could allow patients to avoid potentially dangerous activities such as swimming or driving when their seizure risk is highest, and to potentially take steps (such as additional medication doses) to reduce their seizure risk, similar to how people with asthma know to take extra care to bring their inhalers when pollen levels are high.
“I like to compare it to a weather forecast,” Rao said. “In the past, the field has focused on predicting the exact moment a seizure will occur, which is like predicting when lightning will strike. That’s pretty hard. It may be more useful to be able tell people there is a 5 percent chance of a thunderstorm this week, but a 90 percent chance next week. That kind of information lets you prepare.”
[Abstract+References] Transcutaneous electrical nerve stimulation improves walking capacity and reduces spasticity in stroke survivors: a systematic review and meta-analysis
To evaluate (1) the effectiveness of transcutaneous electrical nerve stimulation (TENS) at improving lower extremity motor recovery in stroke survivors and (2) the optimal stimulation parameters for TENS.
A systematic search was conducted for studies published up to October 2017 using eight electronic databases (CINAHL, ClinicalTrials.gov, the Cochrane Central Register of Controlled Trials, EMBASE, MEDLINE, PEDro, PubMed and Web of Science). Randomized controlled trials that evaluated the effectiveness of the application of TENS at improving lower extremity motor recovery in stroke survivors were assessed for inclusion. Outcomes of interest included plantar flexor spasticity, muscle strength, walking capacity and balance.
In all, 11 studies met the inclusion criteria which involved 439 stroke survivors. The meta-analysis showed that TENS improved walking capacity, as measured by either gait speed or the Timed Up and Go Test (Hedges’ g = 0.392; 95% confidence interval (CI) = 0.178 to 0.606) compared to the placebo or no-treatment control groups. TENS also reduced paretic plantar flexor spasticity, as measured using the Modified Ashworth Scale and Composite Spasticity Scale (Hedges’ g = –0.884; 95% CI = –1.140 to −0.625). The effect of TENS on walking capacity in studies involving 60 minutes per sessions was significant (Hedges’ g = 0.468; 95% CI = 0.201–0.734) but not in study with shorter sessions (20 or 30 minutes) (Hedges’ g = 0.254; 95% CI = –0.106–0.614).
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via Transcutaneous electrical nerve stimulation improves walking capacity and reduces spasticity in stroke survivors: a systematic review and meta-analysisClinical Rehabilitation – Patrick WH Kwong, Gabriel YF Ng, Raymond CK Chung, Shamay SM Ng, 2017
[Abstract] Neurotech: Robotic Assist Devices Show Gains in Walking for Crouch Gait in Cerebral Palsy and Post-Stroke Hemiparesis
ARTICLE IN BRIEF
Three novel robotic assistance devices, one for hemiparetic gait following stroke, and two for crouch gait in children with cerebral palsy, have each demonstrated improved walking in preliminary clinical trials.
For stroke patients, a robotic exosuit made of a soft, clothing-like anchor attached to motorized cables was shown to increase the paretic limb’s forward propulsion and the paretic ankle’s swing phase dorsiflexion in both treadmill and over-ground walking.
For children with crouch gait due to cerebral palsy, one trial used a cable-driven robot called a Tethered Pelvic Assist Device, or TPAD. The laboratory-based device is designed to strengthen the extensor muscles, especially the soleus in the calves, by putting downward pressure on them during training. After six weeks of practice with the device, the children’s posture was more upright, with greater step length and toe clearance, when walking without it.
Also for children with crouch gait, the third study examined the use of a wearable exoskeleton that provides a burst of knee extension assistance at just the right moment when a child or adolescent is walking. None of the seven participants, age 5 to 17, fell while using it, and six of the seven showed postural improvements equivalent to those previously reported from surgery.
While promising, the devices will require far more testing in randomized trials before their true value can be known, said a leading specialist in neurological rehabilitation.
“These are foundational studies; they’re just beginning to get started,” said Bruce H. Dobkin, MD, FRCP, distinguished professor of clinical neurology and director of the Neurological Rehabilitation and Research Program at the Geffen School of Medicine at the University of California, Los Angeles. “The cost, safety, user-friendliness, and ability to use at differing levels of disability severity — all those are major challenges.”
Even so, each of the three devices employs a new kind of robotic assistance unlike any existing on the market.
“Most robotics for neurological injuries are heavy, power-hungry exosuits for people with spinal cord injuries who can’t walk at all,” said a coauthor of the study for stroke patients, Terry D. Ellis, PT, PhD, NCS, director of the Center for Neurorehabilitation at Boston University. “But there’s a whole bunch of people who have disabilities, who can walk, but don’t walk well. They need facilitation or augmentation to restore some of the normal components of walking.”
A ROBOT POST-STROKE
Published in the July 26 edition of Science Translational Medicine, the study of a robotic exosuit tested in nine post-stroke patients used what it called “garment-like, functional textile anchors” rather than a hard, metallic exterior. Worn on only the paretic limb, the suit was designed to be as unobtrusive as possible.
“It’s much more compatible with the real world than a rigid device would be,” said the first author of the paper, Louis N. Awad, PT, DPT, PhD, an assistant professor of physical therapy at Boston University, and a research faculty member at Spaulding Rehabilitation Hospital. “Ordinary clothes are made of soft material. We don’t don a metallic pair of pants and walk out the door. That’s our goal — robotic clothing that helps people with difficulty walking.”
Attached to cables tethered to a belt worn around the hips, the exosuit functioned in synchrony with a wearer’s paretic limb to facilitate an immediate increase in the paretic ankle’s swing phase dorsiflexion and forward propulsion (p< 0.05), according to the paper.
The improved movements resulted in a 20 percent reduction in forward propulsion interlimb asymmetry and a 10 percent reduction in the energy cost of walking, which together were equivalent to a nearly one-third lower metabolic burden — a 32 percent reduction — while walking.
Although the study did include some over-ground walking, it was not designed to test whether the exosuit had any therapeutic effects that might carry over to when patients are not wearing it.
“This is a proof of concept paper,” said Dr. Ellis. “Down the road we need to conduct trials in more ecologically valid environments, and to see if it has therapeutic value. For now we wanted to demonstrate that the device can facilitate more normal walking.”
While applauding the study as “clever,” Dr. Dobkin said it remained to be seen whether the robotic exosuit would prove to have significant therapeutic effects that would stand up in randomized trials in natural environments. He pointed to randomized trials published in recent years showing that peroneal nerve functional electrical stimulators have no greater therapeutic effect than do standard ankle-foot orthoses.
“It’s similar to all the work that was done using the electrical stimulation of the ankle,” Dr. Dobkin said. “The real question is whether it will lead to improved function when you walk over-ground. Walking on a treadmill is not terribly natural.”
He also pointed out that the nine patients in the study were able to walk on average at about two miles per hour. “That’s already pretty fast,” he said. In addition, he said, the 20 percent reduction in interlimb asymmetry is relatively modest.
But, said Dr. Dobkin, people can improve their gait by 20 percent just by sustained practice. “When you see modest changes like this with the device, you wonder if the same changes couldn’t have been achieved without it,” he said.
Steven L. Wolf, PhD, PT, FAPTA, FAHA, professor in the department of rehabilitation medicine at Emory University School of Medicine, pointed out that existing robotic devices to help people who are completely unable to walk can cost patients up to $250,000. Perhaps the exosuit might become an improvement over what presently exists both in terms of function and cost, he said.
“Most existing devices are beautiful but incredibly expensive,” Dr. Wolf said. “Is the bang in the buck? Not as yet, in my opinion. The evidence for persistent benefit from these device is just not there.”
IMPROVING CROUCH GAIT IN CP
The first of the two studies using robotic devices to improve crouch gait in children with cerebral palsy was published on July 26 in Science Robotics, led by senior author Sunil K. Agrawal, PhD, professor of mechanical engineering and rehabilitation medicine at Columbia University.
Rather than directly straighten the children’s posture, Dr. Agrawal’s seemingly contradictory approach was to increase the downward force on their pelvis as they attempted to walk on a treadmill. The tension in each wire, attached to a belt on the pelvis, is modulated in real time by a motor placed around the treadmill in response to motion capture data from cameras. Unlike other robotic devices that have been tested for treating crouch gait, the TPAD has no rigid links to the body, permitting free movement of the legs.
After training in the device for 15 sessions of 16 minutes each over the course of six weeks, the six participants showed enhanced upright posture, improved muscle coordination, increased step length, range of motion of the lower limb angles, toe clearance, and heel-to-toe pattern.
“You can see a marked difference before and after,” Dr. Agrawal said. “We heard from families and the children themselves that they were walking faster, with better posture. Now we have to see if we should use a higher magnitude of downward pull, how long each training session should be, and for how many sessions.”
Commenting on the TPAD study, Dr. Dobkin said, “The kids who were selected for inclusion were not necessarily the kind who get surgery. They had less of a crouch, a little bit more of a push-off. The question is whether training like this will lead to good over-ground walking. They got a hint of that.”
The second crouch-gait study, published on August 23 in Science Translational Medicine, involved a wearable exoskeleton designed for over-land use, and was described by the authors as the first robotic device designed specifically to treat a gait disorder in children and adolescents. Rather than force the lower limb to move in a particular way, “the exoskeleton dynamically changed the posture by introducing bursts of knee extension assistance during discrete portions of the walking cycle, a perturbation that resulted in maintained or increase knee extensor muscle activity during exoskeleton use,” the paper stated.
“In the last decade, there’s been a groundswell of work on exoskeletons, but a majority of them are designed to permit mobility after spinal injury in adults who have lost the ability to walk,” said senior author Thomas Bulea, PhD, a staff scientist in the functional and applied biomechanics section of the rehabilitation medicine department at the National Institutes of Health Clinical Center in Bethesda, MD. “There hasn’t been much done for the pediatric population who just need to improve their walking.”
A coauthor of the paper, Diane L. Damiano, PT, PhD, chief of the section in which Dr. Bulea works, said the purpose of the wearable exoskeleton is different than that of the TPAD device developed by Dr. Agrawal.
“His device is designed to strengthen the calf muscles by increasing the resistance on them,” she said. “His results were good, but this is very different from what we are doing. We have a wearable device. It’s not meant to be used in a lab for training. We’re not necessarily trying to strengthen them, although that would be a desired outcome; we are instead trying to assist their abilities to help them practice being more upright while they walk. This is something that they would wear throughout the day for several months with the goal that their posture will ultimately be improved without the device.”
A surprising observation, she added, was that some children saw it as something cool to wear.
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A study published recently in Science Translational Medicine suggests that the use of a soft suit exoskeleton system helps aid in the facilitation of walking ability among ambulatory patients following a stroke.
Researchers from Harvard University’s Wyss Institute for Biologically Inspired Engineering, the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and Boston University’s (BU) College of Health & Rehabilitation Sciences: Sargent College developed the lightweight, soft, wearable ankle-assisting exosuit, and they they suggest in the study that it could help reinforce normal gait in people with hemiparesis after stroke.
The study centers on the use of the exosuit among nine participants, each of whom recently experienced a stroke, and examines the immediate improvements in walking capability that could be obtained when wearing the suit, dubbed the Restore system, according to a media release from ReWalk Robotics Ltd.
According to the release, the study concludes that improvements in paretic limb function contributed to a 20 +/- 4% reduction in forward propulsion interlimb asymmetry and a 10 +/- 3% reduction in the energy cost of walking, which is equivalent to a 32+/- 9% reduction in the metabolic burden associated with poststroke walking. Relatively low assistance (~12% of biological torques) delivered with a lightweight and nonrestrictive exosuit was sufficient to facilitate more normal walking in ambulatory individuals after stroke.
“This foundational study shows that soft wearable robots can have significant positive impact on gait functions in patients post-stroke, and it is the result of a translational-focused multidisciplinary team of engineers, designers, biomechanists, physical therapists, and most importantly patients who volunteered for this study and gave valuable feedback that guided our research,” says Wyss Core Faculty member Conor Walsh, who is also the John L. Loeb Associate Professor of Engineering and Applied Sciences at SEAS and the Founder of the Harvard Biodesign Lab, in the release.
ReWalk is working with the Wyss Institute on the development of lightweight designs to complete clinical studies, pursue regulatory approvals, and commercialize the systems on a global scale. The first commercial application will be for stroke survivors, followed by Multiple Sclerosis patients and then additional applications.
“Exoskeletons are now a commercially available, disruptive technology that have changed the lives of many individuals in the paraplegic community,” states ReWalk CEO Larry Jasinski, in the release. “The ongoing research at the Wyss Institute on soft exosuits adds a new dimension to exoskeletons that can potentially meet the needs of individuals that have had a stroke, as well as for those diagnosed with Multiple Sclerosis, Parkinson’s disease or people who have limitations in walking.”
[Source(s): ReWalk Robotics Ltd, PR Newswire, Science Daily]
[ARTICLE] Effects of dual-task and walking speed on gait variability in people with chronic ankle instability: a cross-sectional study – Full Text
Recent evidence suggests that impaired central sensorimotor integration may contribute to deficits in movement control experienced by people with chronic ankle instability (CAI). This study compared the effects of dual-task and walking speed on gait variability in individuals with and without CAI.
Sixteen subjects with CAI and 16 age- and gender-matched, able-bodied controls participated in this study. Stride time variability and stride length variability were measured on a treadmill under four different conditions: self-paced walking, self-paced walking with dual-task, fast walking, and fast walking with dual-task.
Under self-paced walking (without dual-task) there was no difference in stride time variability between CAI and control groups (P = 0.346). In the control group, compared to self-paced walking, stride time variability decreased in all conditions: self-paced walking with dual-task, fast speed, and fast speed with dual-task (P = 0.011, P = 0.016, P = 0.001, respectively). However, in the CAI group, compared to self-paced walking, decreased stride time variability was demonstrated only in the fast speed with dual-task condition (P = 1.000, P = 0.471, P = 0.008; respectively). Stride length variability did not change under any condition in either group.
Subjects with CAI and healthy controls reduced their stride time variability in response to challenging walking conditions; however, the pattern of change was different. A higher level of gait disturbance was required to cause a change in walking in the CAI group compared to healthy individuals, which may indicate lower adaptability of the sensorimotor system. Clinicians may use this information and employ activities to enhance sensorimotor control during gait, when designing intervention programs for people with CAI.
The study was registered with the Clinical Trials network (registration NCT02745834, registration date 15/3/2016).
Recurrent ankle sprains occur in up to 40% of individuals who have previously experienced a lateral ankle sprain [1, 2]. Individuals who report residual symptoms, which include repetitive episodes of ‘giving way’ and subjective feeling of ankle joint instability are termed as having chronic ankle instability (CAI) . The cause of these symptoms and the high frequency of recurrent ankle sprain is not fully understood . It has been suggested that the residual joint instability and the high reoccurrence rates can be attributed to loss of sensory input from articular mechano-receptors, decreased muscle strength, mechanical instability of the ankle joint, and reduced ankle range of motion [5, 6].
Recent evidence suggests that deficits in central neural sensorimotor integration can contribute to impaired movement control in people with CAI [7, 8, 9, 10, 11, 12, 13, 14]. For example, Springer et al.  assessed the correlation between single-limb stance postural control (Overall Stability Index) and shoulder position sense (Absolute Error Score) among people with CAI and healthy controls. Correlations between the lower and upper limbs were observed only in the healthy controls, indicating altered sensorimotor integration in the CAI group. Several studies have observed altered gait mechanism in people with CAI, which was explained by compromised central nervous system (CNS) control [9, 14, 15, 16]. It was shown that people with CAI have a typical gait pattern of increased inversion kinematics and kinetics, lateral shift of body weight, increased hip flexion during terminal swing to mid stance, reduced hip extension and increased knee flexion during terminal stance to initial swing, and slow weight transfer at the beginning and end of the stance [15, 16, 17]. Altered biomechanical strategies during gait initiation and termination tasks (e.g., reduced center of pressure displacement), have also been demonstrated in this population [9, 14]. Studies that assessed movement variability, such as knee and hip joint motions during single leg jump landing, identified differences between individuals with and without CAI, which may also indicate central motor programming deficits [10, 11, 12, 13]. Hence, further investigation of motor control adaptations may contribute to understanding the underlying neurophysiologic mechanisms of CAI.
Gait speed and other spatio-temporal parameters during daily activities should reflect behavioral goals and environmental conditions . Studies revealed that walking speed has a significant effect on joint coordination pattern and gait variability [18, 19, 20]. Therefore, assessing gait variability under challenging situations such as walking at different speeds might test CNS flexibility in controlling gait [19, 20]. Moreover, based on the understanding that for many daily activities even a fully intact motor control system requires attention and cognitive resources , the dual-task paradigm has been used to provide insight into the demands of postural control and gait on attention. Performance of a cognitive task has been shown to decrease postural control in participants with CAI as compared to healthy controls [7, 22]. However, no previous study examined the impact of cognitive task and walking speed on gait performance in subjects with CAI.
Balance during walking is reflected by precise spatial and temporal control of foot placement. Stride to stride fluctuations in time and length are related to control of the rhythmic walking mechanism. Thus, previous research has suggested that studying gait variability is a reliable way to quantify locomotion . The mechanism of adjusting movement variability is considered beneficial for coping with changes, maintaining stability, preventing injury, and attaining higher motor skills . Performing a cognitive task while walking or while altering self-paced walking speed has been related to changes in gait variability in populations with neurological and musculoskeletal pathologies, as well in healthy young individuals [25, 26, 27, 28]. Yet, there is no consensus in the literature as to how to interpret these changes. Decreased variability while performing demanding gait tasks may reflect voluntary gait adaptation toward a more conservative gait pattern . Alternatively, it has been suggested that increased variability may indicate CNS flexibility and adaptability to changes in task demands . A possible central sensorimotor control deficit in people with CAI may constrain the ability of the CNS to adjust to different task demands; thus, affecting central control over gait variability and reducing the ability to cope with varied tasks. Consequently, testing the mechanism of adjusting gait variability as a response to complex walking conditions in people with CAI compared to healthy controls may provide more information on sensorimotor control in this population.
The present study was designed to compare the effects of dual-task and walking speed on gait variability in individuals with and without CAI. Previous reports, including a meta-analysis, indicated that simple postural tasks do not always discriminate between participants with CAI and those without [6, 8, 30]. Consequently, we hypothesized that gait variability among individuals with and without CAI will be similar during “normal” self-paced walking, whereas gait will vary under complex walking conditions.[…]
Walking is a complex motor behavior with a special relevance in clinical neurology. Many neurological diseases, such as Parkinson’s disease and stroke, are characterized by gait disorders whose neurofunctional correlates are poorly investigated. Indeed, the analysis of real walking with the standard neuroimaging techniques poses strong challenges, and only a few studies on motor imagery or walking observation have been performed so far. Functional near-infrared spectroscopy (fNIRS) is becoming an important research tool to assess functional activity in neurological populations or for special tasks, such as walking, because it allows investigating brain hemodynamic activity in an ecological setting, without strong immobility constraints. A systematic review following PRISMA guidelines was conducted on the fNIRS-based examination of gait disorders. Twelve of the initial yield of 489 articles have been included in this review. The lesson learnt from these studies suggest that oxy-hemoglobin levels within the prefrontal and premotor cortices are more sensitive to compensation strategies reflecting postural control and restoration of gait disorders. Although this field of study is in its relative infancy, the evidence provided encourages the translation of fNIRS in clinical practice, as it offers a unique opportunity to explore in depth the activity of the cortical motor system during real walking in neurological patients. We also discuss to what extent fNIRS may be applied for assessing the effectiveness of rehabilitation programs.
Walking is one of the most fundamental motor functions in humans,1–3 often impaired in some focal neurological conditions (ie, stroke), or neurodegenerative diseases, such as Parkinson’s disease (PD).4 Worldwide almost two thirds of people over 70 years old suffer from gait disorders, and because of the progressively ageing population, an increasing pressure on health care systems is expected in the coming years.5
Although the physiological basis of walking is well understood, pathophysiological mechanisms in neurological patients have been poorly described. This is caused by the difficulty to assess in vivo neuronal processes during overt movements.
During the past 20 years, functional magnetic resonance imaging (fMRI) has been the preferred instrument to investigate mechanisms underlying movement control6 as well as movement disorders.7 fMRI allows measuring the blood oxygenation level-dependent (BOLD) signal that, relying on variations in deoxy-hemoglobin (deoxyHb) concentrations, provides an indirect measure of functional activity of the human brain.8 Patterns of activation/deactivation and connectivity across brain regions can be detected with a very high spatial resolution for both cortical and subcortical structures. This technique, however, is characterized by severe limitations and constraints about motion artifacts and only small movements are allowed inside the scanner. This entails dramatic compromises on the experimental design and on the inclusion/exclusion criteria. Multiple solutions have been attempted to overcome such limitations. For instance, many neuroimaging studies have been performed on the motor imagery,9,10 but imaging can be different from subject to subject,11 and imagined walking and actual walking engage different brain networks.12 Other authors have suggested the application of virtual reality,13 and there have been a few attempts to allow an almost real-walking sequence while scanning with fMRI.14,15Additional opportunities to investigate the mechanisms sustaining walking control include the use of surrogate tasks in the scanner as proxy of walking tasks,16 or to “freeze” brain activations during walking using positron emission tomography (PET) radiotracers, which allow the retrospective identification of activation patterns, albeit with some uncertainties and low spatial and temporal resolution.12
Therefore, until now there has not been an ecological way to noninvasively assess neurophysiological correlates of walking processes in gait disorders.
Functional near-infrared spectroscopy (fNIRS) is becoming an important research tool to assess functional activity in special populations (neurological and psychiatric patients)17 or for special tasks.18–21 fNIRS is a noninvasive optical imaging technique that, similarly to fMRI, measures the hemodynamic response to infer the underlying neural activity. Optical imaging is based on near-infrared (650-1000 nm) light propagation into scattering tissues and its absorption by 2 major chromophores in the brain, oxy-hemoglobin (oxyHb) and deoxyHb, which show specific absorption spectra depending on the wavelength of the photons.22 Typically, an fNIRS apparatus is composed of a light source that is coupled to the participant’s head via either light-emitting diodes (LEDs) or through fiber-optical bundles with a detector that receives the light after it has been scattered through the tissue. A variation of the optical density of the photons measured by detectors depends on the absorption of the biological tissues (Figure 1A). Using more than one wavelength and applying the modified Beer-Lambert law, it is possible to infer on the changes of oxyHb and deoxyHb concentrations.23 fNIRS has a number of definite advantages compared to fMRI, its major competitor: (a) it does not pose immobility constrains,25 (b) is portable,26 (c) allows recording during real walking,27 (d) allows long-lasting recordings, (e) it does not produce any noise, (f) it makes possible the investigation of brain activity during sleep,28 (f) it allows to obtain a richer picture of the neurovascular coupling as it measures changes in both oxyHb and deoxyHb concentration with high temporal resolution (up to milliseconds). High temporal resolution is usually not mandatory for the investigation of the hemodynamic response whose dynamic takes at least 3 to 5 seconds, but it can be useful for the study of transient hemodynamic activity like the initial dip29 or to detect subtle temporal variations in the latency of the hemodynamic response across different experimental conditions.19,21,30 The major drawback of fNIRS in comparison to fMRI is its lower spatial resolution (few centimeters under the skull) and its lack of sensitivity to subcortical regions.18,19 However, this might be considered a minor limitation, as there is a large body of evidence suggesting that (a) cortical mechanisms take place in walking,31 (b) the organization of the motor system is distributed along large brain regions,32and (c) the function of subcortical structures is mirrored in the cerebral cortex.33
74 for the considered source-detector pair to the head/brain structures. (A, B, and C) Lower row: Examples of fNIRS experimental device used for assessing brain activity during real walking tasks. These fNIRS approaches included either commercial device, such as (A) wireless portable fNIRS system (NIRx; Germany) or support systems for treadmill walking activity with body weight support24 (B) or with free movement range (C).Illustration of penetration depth of near-infrared light into the tissue in a probe configuration used to investigate motor performances during walking task (upper row). The picture shows brain reconstruction from a high-resolution anatomical MRI. The spheres placed over the skull correspond to vitamin E capsules employed during the MRI to mark the positions of the optodes and to allow the coregistration of the individual anatomy together with the optode position. In this illustration, only the photons propagation from one source (S) to one detector (D) have been simulated. The yellow-red scale indicates the degree of sensitivity
[Abstract] Changes in lower limb muscle activity after walking on a split-belt treadmill in individuals post-stroke
Background: There is growing evidence that stroke survivors can adapt and improve step length symmetry in the context of split-belt treadmill (SBT) walking. However, less knowledge exists about the strategies involved for such adaptations. This study analyzed lower limb muscle activity in individuals post-stroke related to SBT-induced changes in step length.
Methods: Step length and surface EMG activity of six lower limb muscles were evaluated in individuals post-stroke (n=16) during (adaptation) and after (after-effects) walking at unequal belt speeds.
Results: During adaptation, significant increases in EMG activity were mainly found in proximal muscles (p⩽0.023), whereas after-effects were observed particularly in the distal muscles. The plantarflexor EMG increased after walking on the slow belt (p⩽0.023) and the dorsiflexors predominantly after walking on the fast belt (p⩽0.017) for both, nonparetic and paretic-fast conditions. Correlation analysis revealed that after-effects in step length were mainly associated with changes in distal paretic muscle activity (0.522⩽ r ⩽0.663) but not with functional deficits. Based on our results, SBT walking could be relevant for training individuals post-stroke who present shorter paretic step length combined with dorsiflexor weakness, or individuals with shorter nonparetic step length and plantarflexor weakness.