Search

Individuals with motor incomplete spinal cord injuries (iSCI) often have impaired abilities to maintain upright balance. For able-bodied (AB) individuals, the ankle and hip joint accelerations are in antiphase to minimize the postural sway during quiet standing. Here we investigated how interjoint coordination between the ankle and hip joints was affected in individuals with iSCI, leading to their larger postural sway during quiet standing. Data from 16 individuals with iSCI, 14 age- and sex-matched AB individuals, and 13 young AB individuals were analyzed. The participants performed quiet standing during which kinematic and kinetic data were recorded. Postural sway was quantified using center-of-pressure velocity and center-of-mass acceleration. Individual ankle and hip joint kinematics were quantified, and the interjoint coordination was assessed using the cancellation index (CI), goal-equivalent variance (GEV), nongoal-equivalent variance (NGEV), and uncontrolled manifold (UCM) ratio. Individuals with iSCI displayed greater postural sway compared with AB individuals. The contribution of ankle angular acceleration toward one's sway was significantly greater for those with iSCI compared with AB groups. CI and the UCM ratios were not statistically different between the groups, while GEV and NGEV were significantly greater for the iSCI group compared with the AB groups. We demonstrated that individuals with iSCI show larger postural sway compared with the AB individuals during quiet standing, primarily due to larger ankle joint acceleration. We also demonstrated that the interjoint coordination between ankle and hip joint is not affected in individuals with iSCI, which is not successfully able to reduce the large COM acceleration.

Background Individuals with incomplete spinal cord injury (iSCI) demonstrate greater postural sway and increased dependency on vision to maintain balance compared to able-bodied individuals. Research on standing balance after iSCI has focused on the joint contribution of the lower limbs; however, inter-limb synchrony in quiet standing is a sensitive measure of individual limb contributions to standing balance control in other neurological populations. It is unknown if and how reduced inter-limb synchrony contributes to the poor standing balance of individuals with iSCI. Research question How does an iSCI affect inter-limb synchrony and weight-bearing symmetry in standing? Methods Eighteen individuals with non-progressive motor iSCI and 15 age- and sex-matched able-bodied individuals (M-AB) were included in the study. Participants stood in a standardized position on two adjacent force plates in eyes open and closed conditions for 70 s per condition. Net centre-of-pressure (COP) root mean square (RMS), net COP velocity, COP inter-limb synchrony (i.e. cross-correlation between left and right COP), and weight-bearing asymmetry (i.e. vertical force from each limb over total vertical force) were calculated. Muscle strength of the lower limbs was assessed with manual muscle testing. Results Individuals with iSCI demonstrated reduced inter-limb synchrony when standing with eyes open and eyes closed, but did not differ to M-AB with respect to weight-bearing asymmetry. They also produced greater net COP RMS and velocity when compared to M-AB. Muscle strength of the two lower limbs demonstrated an overall asymmetry in individuals with iSCI. Significance Individuals with iSCI demonstrated impaired balance control as evidenced by reduced inter-limb synchrony and greater COP RMS and velocity compared to M-AB individuals. This increased understanding of how balance control is impaired following iSCI may inform balance assessment and intervention for this population. Future work examining the association between inter-limb synchrony and the occurrence of falls in iSCI is warranted.

Previous findings indicate that co-contractions of plantarflexors and dorsiflexors during quiet standing increase the ankle mechanical joint stiffness, resulting in increased postural sway. Balance impairments in individuals with incomplete spinal cord injury (iSCI) may be due to co-contractions like in other individuals with reduced balance ability. Here we investigated the effect of co-contraction between plantar- and dorsiflexors on postural balance in individuals with iSCI (iSCI-group) and able-bodied individuals (AB-group). Thirteen able-bodied individuals and 13 individuals with iSCI were asked to perform quiet standing with their eyes open (EO) and eyes closed (EC). Kinetics and electromyograms from the tibialis anterior (TA), soleus and medial gastrocnemius were collected bilaterally. The iSCI-group exhibited more co-contractions than the AB-group (EO: 0.208% vs. 75.163%, p = 0.004; EC: 1.767% vs. 92.373%, p = 0.016). Furthermore, postural sway was larger during co-contractions than during no co-contraction in the iSCI-group (EO: 1.405 cm/s

Transcutaneous neuromuscular electrical stimulation (NMES) can be used to activate the quadriceps femoris muscle to produce knee extension torque via seven distinct motor points, defined as the most sensitive locations on the muscle belly to electrical stimuli. However, it remains unclear how much individual motor points of the quadriceps femoris muscle contribute to the knee joint torque. Here we systematically investigated the contribution of each motor point of the quadriceps femoris muscle to the knee joint torque produced by paired electrical stimuli. Ten able-bodied individuals participated in this study. Paired electrical stimuli was applied by delivering electrical impulses on the motor points in all combinations among seven motor points (i.e., totaling to 127 combinations) at two different stimulation intensities (i.e., 25% and 50% of the maximum) while recording isometric knee joint torque. The contribution of individual motor points was estimated using statistical analyses. We found that a linear addition of twitch torques induced by single motor point stimulus overestimated the twitch torques induced by multiple motor point stimulations, suggesting overlaps in muscle fibres activated by each motor point. Using multiple linear regressions, we identified the average contribution of each motor point to the knee extension torque during paired electrical stimuli and found significant differences between these torque contributions. We demonstrated that seven distinct motor points can be activated for the quadriceps muscle group using paired electrical stimuli and identified the contribution of each motor point to knee extension torque during twitch muscle contraction; these findings provide useful information to design rehabilitation using NMES on quadriceps femoris muscles.

OBJECTIVE The study objective was to assess the feasibility of stimulating the lower trapezius (LT), the upper trapezius (UT) and serratus anterior (SA) muscles along with anterior or middle deltoid, using surface functional electrical stimulation (FES). The secondary aim was to understand the effects of LT, UT, and SA stimulation on maximum arm reach achieved in shoulder flexion and abduction. DESIGN Single arm interventional study. SETTING Inpatient Rehabilitation Hospital. PARTICIPANTS Ten healthy volunteers. INTERVENTION Participants completed 10 trials for each of the 3 conditions in flexion and abduction, i.e. (1) Active voluntary flexion or abduction, (2) FES for anterior deltoid for flexion or middle deltoid for abduction, and (3) FES for LT, UT, and SA along with anterior deltoid for flexion or middle deltoid for abduction. OUTCOME MEASURES Maximum arm reach and percent angle relative to the voluntary movement were computed from motion capture data for each condition. Wilcoxon signed-rank test was used to compare the maximum reach between two FES conditions. RESULTS The study results showed that all three interscapular muscles can be stimulated using surface FES. Maximum reach in abduction was greater for FES of middle deltoid along with the interscapular muscles (51.77° ± 17.54°) compared to FES for middle deltoid alone (43.76° ± 15.32°; Z = -2.701, P = 0.007). Maximum reach in flexion for FES of anterior deltoid, along with interscapular muscles, was similar to that during FES of anterior deltoid alone. CONCLUSION Interscapular muscles can be stimulated using surface FES devices and should be engaged during rehabilitation as appropriate.

Previous findings indicate that co-contractions of plantarflexors and dorsiflexors during quiet standing increase the ankle mechanical joint stiffness, resulting in increased postural sway. Balance impairments in individuals with incomplete spinal cord injury (iSCI) may be due to co-contractions like in other individuals with reduced balance ability. Here we investigated the effect of co-contraction between plantar- and dorsiflexors on postural balance in individuals with iSCI (iSCI-group) and able-bodied individuals (AB-group). Thirteen able-bodied individuals and 13 individuals with iSCI were asked to perform quiet standing with their eyes open (EO) and eyes closed (EC). Kinetics and electromyograms from the tibialis anterior (TA), soleus and medial gastrocnemius were collected bilaterally. The iSCI-group exhibited more co-contractions than the AB-group (EO: 0.208% vs. 75.163%, p = 0.004; EC: 1.767% vs. 92.373%, p = 0.016). Furthermore, postural sway was larger during co-contractions than during no co-contraction in the iSCI-group (EO: 1.405 cm/s2 vs. 0.867 cm/s2, p = 0.023; EC: 1.831 cm/s2 vs. 1.179 cm/s2, p = 0.030), but no differences were found for the AB-group (EO: 0.393 cm/s2 vs. 0.499 cm/s2, p = 1.00; EC: 0.686 cm/s2 vs. 0.654 cm/s2, p = 1.00). To investigate the mechanism, we performed a computational simulation study using an inverted pendulum model and linear controllers. An increase of mechanical stiffness in the simulated iSCI-group resulted in increased postural sway (EO: 2.520 cm/s2 vs. 1.174 cm/s2, p 2 vs. 1.836 cm/s2, p 2 vs. 0.658 cm/s2, p = 1.00; EC: 0.943 cm/s2 vs. 0.926 cm/s2, p = 0.190). Thus, we demonstrated that co-contractions may be a compensatory strategy for individuals with iSCI to accommodate for decreased motor function, but co-contractions may result in increased ankle mechanical joint stiffness and consequently postural sway.

Background Slipping is one of the leading causes of falls among older adults. Older adults are considered to walk with a small anteroposterior (AP) component and a large mediolateral (ML) component of the required coefficient of friction (RCOF) owing to a short step length and a wide step width, respectively. However, limited information is available. Research question What are the effects of aging on the resultant RCOF (RCOFres) and its ML (RCOFML) and AP (RCOFAP) components during straight walking? Methods We used the kinetic and kinematic data of 188 participants aged 20–77 years from a publicly available database (National Institute of Advanced Industrial Science and Technology Gait Database 2015). The participants were divided into the following three groups: young group (n = 56; age range, 20–34 years), middle-aged group (n = 50; age range, 35–64 years), and old group (n = 82; age range, 65–77 years). Results The RCOFres and RCOFAP were lower in the old group than in the other groups, indicating a lower slip risk in this group. However, the RCOFML was higher and the step width was greater in the old group than in the other groups. The higher RCOFML and lower RCOFAP in the old group might be associated with slips in a more lateral direction. Significance Our findings suggest that older adults have a high risk of slipping in a more lateral direction. Shoes with high-slip resistance in the lateral direction are recommended to prevent hazardous lateral slips among older adults.

Background: The purpose of this study was to examine the impact of functional electrical stimulation (FES) induced co-activation of trunk muscles during quiet sitting. We hypothesized that FES applied to the trunk muscles will increase trunk stiffness. The objectives of this study were to: 1) compare the center of pressure (COP) fluctuations during unsupported and FES-assisted quiet sitting - an experimental study and; 2) investigate how FES influences sitting balance - an analytical (simulation) study. Methods The experimental study involved 15 able-bodied individuals who were seated on an instrumented chair. During the experiment, COP of the body projected on the seating surface was calculated to compare sitting stability of participants during unsupported and FES-assisted quiet sitting. The analytical (simulation) study examined dynamics of quiet sitting using an inverted pendulum model, representing the body, and a proportional-derivative (PD) controller, representing the central nervous system control. This model was used to analyze the relationship between increased trunk stiffness and COP fluctuations. Results In the experimental study, the COP fluctuations showed that: i) the mean velocity, mean frequency and the power frequency were higher during FES-assisted sitting; ii) the frequency dispersion for anterior-posterior fluctuations was smaller during FES-assisted sitting; and iii) the mean distance, range and centroidal frequency did not change during FES-assisted sitting. The analytical (simulation) study showed that increased mechanical stiffness of the trunk had the same effect on COP fluctuations as the FES. Conclusions The results of this study suggest that FES applied to the key trunk muscles increases the speed of the COP fluctuations by increasing the trunk stiffness during quiet sitting.

Background Individuals with an incomplete spinal cord injury (iSCI) are highly susceptible to falls during periods of walking or standing. We recently reported the findings of a novel intervention combining functional electrical stimulation with visual feedback balance training (FES + VFBT) on standing balance abilities among five individuals with motor iSCI. However, the previous publication did not report the perceived impact of the intervention on the participants’ lives. In this report, the experiences of these five individuals with incomplete spinal cord injury (iSCI) who had recently completed the four-week balance training program are described. Methods Five individuals with a motor iSCI took part in this study. Each individual was at least 12 months post-injury, capable of unassisted standing for 60 s and had a Berg Balance Scale Score Results Three themes were identified from the collected transcripts: (1) Perceived benefits across International Classification of Functioning, Disability and Health levels; (2) Change in perceived fall risk and confidence; (3) Motivation to keep going. Conclusions Participation in the FES + VFBT program resulted in perceived benefits that led to meaningful improvements in activities of daily living. Following completion of the training, individuals felt they still had the capacity to improve. Individuals felt they had increased their balance confidence, while a few participants also reported a decrease in their risk of falling. The inclusion of qualitative inquiry allows for the evaluation of the meaningfulness of an intervention and its perceived impact on the lives of the participants. Trial registration: NCT04262414 (retrospectively registered February 10, 2020)

The nociceptive flexion reflex (NFR) is used in neurophysiological research as an objective measure of nociception. NFR thresholds are reduced in numerous chronic pain pathologies, which are indicative of common central hyperexcitability within conditions. However, variation exists in both the NFR assessment and determinants of NFR threshold among research groups. Our purpose was to provide a review of the recent literature to (a) confirm the NFR threshold’s efficacy in identifying those with chronic pain compared to controls and (b) provide a narrative synthesis on the current methodology used to assess the NFR in clinical populations. We conducted a review of multiple databases (MEDLINE, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Google Scholar and Cochrane Library), including articles that reported controlled clinical studies of humans, in English, comparing NFR thresholds within chronic pain conditions to matched control subjects, published since the last NFR review in 2010. Our search resulted in nine studies included in our narrative synthesis and eight studies included in a meta-analysis. There was a significant pooled standardized mean difference in NFR threshold between chronic pain conditions and controls (−0.94, 95% confidence interval (CI) −1.33 to −0.55, p 2 = 87%, τ2 = 0.41, Q = 76.13, the degrees of freedom (df) = 11, p

Background The nociceptive flexion reflex is a physiological, polysynaptic reflex and refers to the level that an appropriate withdrawal response activates when a painful stimulus is detected. The nociceptive flexion reflex threshold (NFRthr) is defined as the lowest noxious stimulation intensity required to trigger a reflex motor response. Despite wide utilization and reports of the NFRthr, there has been no consensus on a standard and/or best method in assessment of the NFRthr. Objective To systematically review the literature that compared the NFRthr between individuals with fibromyalgia (FM) and healthy controls; and to identify a source of heterogeneity in these trials. Methods Employing the Cochrane methodology, we systematically searched Ovid MEDLINE, Embase, Cochrane Clinical Answers, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and PsycINFO for clinical case-controlled trials assessing the NFRthr in individuals with and without fibromyalgia from inception to July 2019. Selected articles were passed for data extraction and meta-analyses. We utilized the random-effects model for meta-analysis assuming the true effect size may vary between studies. The sample sizes as a possible source of heterogeneity in multiple meta-regressions were investigated. This systematic review and meta-analysis were registered in PROSPERO before data extraction. Results Nine studies met our criteria and were included in the meta-analysis. Methodologies and settings varied between studies, eg, stimulation intensity, duration, and the current increments. Only two articles comprehensively described and reported details about electromyogram amplification, latency, and sampling rate. Evidence from 423 patients with fibromyalgia and 326 healthy individuals suggested that there may not be a meaningful decreased NFRthr in patients (overall mean difference = -3.16; 95% CI:-6.82 to 0.50; Z = 1.69; P=0.09). Published effect sizes were not homogenous (I2 = 0.91, τ2 = 25.04, χ2 = 91.22, df = 8, P < 0.00001). The multiple meta-regression analyses indicated that total and female sample sizes might be the main sources of heterogeneity for the effect sizes SStotal = -0.0570, P = 0.040; SSfemale = -0.0569; P = 0.047. Conclusion Evidence suggests that the nociceptive flexion reflex threshold may not be different between patients with fibromyalgia and healthy controls. A unified and rigorous methodology and sample size calculation (probably sex specific investigation) is required for the assessment of nociceptive flexion reflex threshold in patients with fibromyalgia.

Objective: To evaluate test-retest reliability, agreement, and convergent validity of the Lean-and-Release test for the assessment of reactive stepping among individuals with incomplete spinal cord injury or disease (iSCI/D). Design: Multi-center cross-sectional multiple test design. Setting: SCI/D rehabilitation hospital and biomechanics laboratory. Participants: Individuals with motor incomplete SCI/D (iSCI/D). Interventions: None. Outcome Measures: Twenty-six participants attended two sessions to complete the Lean-and-Release test and a battery of clinical tests. Behavioral (i.e. one-step, multi-step, loss of balance) and temporal (i.e. timing of foot off, foot contact, swing of reactive step) parameters were measured. Test-retest reliability was determined with intraclass correlation coefficients, and agreement was evaluated with Bland–Altman plots. Convergent validity was assessed through correlations with clinical tests. Results: The behavioral responses were reliable for the Lean-and-Release test (ICC = 0.76), but foot contact was the only reliable temporal parameter using data from a single site (ICC = 0.79). All variables showed agreement according to the Bland–Altman plots. The behavioral responses correlated with scores of lower extremity strength (0.54, P

Background Myofascial pain syndrome (MPS) is a prevalent chronic pain disorder primarily characterized by myofascial trigger points (MTrPs). There is limited knowledge on the pathophysiology and mechanisms underlying MTrP and its development. Research has previously demonstrated the identification of MTrPs using ultrasound and vibration sonoelastography, although there is some contradictory evidence regarding if MTrPs present as hyper or hypoechoic regions. Electromyography (EMG) investigations of MTrP have demonstrated that MTrPs are usually located proximal to innervation zones where the peak surface EMG signals are obtained from. Central sensitization has been proposed as the primary mechanism underlying MTrP development. Central sensitization is associated with hyperexcitability of neuronal responses to normal or noxious stimuli. There is a need for a study that measures ultrasound image textural changes and motor unit activity responses in the muscle following sensitization. The purpose of this study is to determine whether sensitizing healthy muscle using capsaicin induces a regional change in image texture variables within the specific and surrounding muscles, as well as the motor unit frequency and amplitude changes that accompany them. This is an exploratory trial that aims to provide preliminary evidence on whether central sensitization is a direct cause of taut band and MTrP development. Methods Ethical approval was obtained from the University Health Network (UHN) Research Ethics Board. This proposed study is a single centered, factorial, randomized placebo-controlled trial with two independent variables, depth of capsaicin application and dose of capsaicin, for a total of six treatment arms and three control treatment groups. Discussion This will be the first study that assesses the B-mode ultrasound image texture of induced sensitized muscles and will provide more evidence on muscle motor unit activity and regional changes of central sensitization. Findings from this study may support one of few hypotheses proposed delineating the involvement of central sensitization in the development of trigger points. Trial registration National Institutes of Health ClinicalTrials.gov NCT03944889. Registered on May 07, 2019

BACKGROUND The nociceptive flexion reflex is a physiological, polysynaptic reflex triggered by a nociceptive stimulus activating a withdrawal response. In chronic musculoskeletal-related pain conditions, a decreased nociceptive flexion reflex threshold has been suggested as a possible recognition evidence for central sensitization that may cause alteration of central nervous system processing. OBJECTIVE The aim of the study was to systematically review reported comparisons of the nociceptive flexion reflex threshold in chronic pain patients and healthy individuals. METHODS Electronic databases covering studies published between January 1990 and December 2019 were systematically searched. After application of exclusion criteria, 20 studies including 28 trials were included in this review. For meta-analysis, we used a random-effects model and funnel plot for publication bias. This research was registered at PROSPERO (CRD42019140354). RESULTS Compared with healthy controls, standardized mean differences in nociceptive flexion reflex threshold were significantly lower in the total sample of chronic pain patients. Subgroup analysis indicated a homogenous decreased nociceptive flexion reflex threshold in studies reporting fibromyalgia, chronic pain, and joint pain while heterogeneity existed in other included pain conditions. CONCLUSIONS A lower nociceptive flexion reflex threshold in patients experiencing chronic pain conditions may imply hyperexcitability in central nervous system processing. As a preliminary study, the findings would act as a basis for developing a methodology assisting current clinical practices.

Gait disturbances are common in individuals with Parkinson's disease (PD). Although the basic patterns of walking are thought to be controlled by the brainstem and spinal networks, recent studies have found significant corticomuscular coherence in healthy individuals during walking. However, it still remains unknown how PD affects the cortical control of muscles during walking. As PD typically develops in older adults, it is important to investigate the effects of both aging and PD when examining disorders in patients with PD. Here, we assessed the effects of PD and aging on corticomuscular communication during walking by investigating corticomuscular coherence. We recorded electroencephalographic and electromyographic signals in 10 individuals with PD, 9 healthy older individuals, and 15 healthy young individuals. We assessed the corticomuscular coherence between the motor cortex and two lower leg muscles, tibialis anterior (TA) and medial gastrocnemius, during walking. Older and young groups showed sharp peaks in muscle activation patterns at specific gait phases, whereas the PD group showed prolonged patterns. Smaller corticomuscular coherence was found in the PD group compared with the healthy older group in the α band (8-12 Hz) for both muscles, and in the β band (16-32 Hz) for TA. Older and young groups did not differ in the magnitude of corticomuscular coherence. Our results indicated that PD decreased the corticomuscular coherence during walking, whereas it was not affected by aging. This lower corticomuscular coherence in PD may indicate lower-than-normal corticomuscular communication, although direct or indirect communication is unknown, and may cause impaired muscle control during walking.NEW & NOTEWORTHY Mechanisms behind how Parkinson's disease (PD) affects cortical control of muscles during walking remain unclear. As PD typically develops in the elderly, investigation of aging effects is important to examine deficits regarding PD. Here, we demonstrated that PD causes weak corticomuscular synchronization during walking, but aging does not. This lower-than-normal corticomuscular communication may cause impaired muscle control during walking.

Individuals with an incomplete spinal cord injury (iSCI) are highly susceptible to falls during walking or standing. Our objective was to evaluate a therapeutic tool for standing balance that combined functional electrical stimulation, applied bilaterally to the plantarflexors and dorsiflexors, with visual feedback balance training (FES+VFBT). Five adults with iSCI completed 12 FES+VFBT sessions over 4 weeks. During the training sessions, participants completed each of the four balance exercises twice. Visual feedback of the center-of-pressure (COP) location was provided as participants completed the balance exercises and received FES to assist with performance of the exercises. A closed-loop FES system was used in which the COP was continually monitored and the level of electrical current administered was automatically adjusted. Balance abilities were assessed pre- and post- training using clinical balance scales (i.e., Berg Balance Scale, Mini-Balance Evaluation Systems Test, and Activities-specific Balance Confidence Scale) and biomechanical assessments (i.e., postural sway measures and limits of stability test during standing). User acceptability was explored through semi-structured interviews. Improvements were seen for four of the five participants on at least one of the clinical scales following completion of the training intervention. All participants showed greater maximal COP excursion area during the limits of stability test after the training intervention, whereas only one participant demonstrated a reduction in postural sway. Specific components of FES+VFBT, including the ability to safely practice challenging balance exercises, were deemed important by the participants. These results suggest that FES+VFBT has potential as an intervention for standing balance after iSCI.

Recent work suggests that functional electrical stimulation can be used to enhance dynamic trunk stability following spinal cord injury. In this context, knowledge of the relation between trunk kinematics and muscle activation in non-disabled individuals may assist in developing kinematics-based neuroprostheses. Our objective was therefore to predict the activation profiles of the major trunk muscles from trunk kinematics following multi-directional perturbations during sitting. Trunk motion and electromyograms (EMG) from ten major trunk muscles were acquired in twelve non-disabled, seated individuals who experienced a force of approximately 200 N applied to the trunk in eight horizontal directions. A linear, time-invariant model with feedback gains on angular trunk displacement, velocity, and acceleration was optimized to predict the EMG from trunk kinematics. For each muscle, only the three directions that produced the largest EMG response were considered. Our results indicate that the time course of the processed EMG was similar across muscles and directions and that the model accounted for 68–92% of the EMG variance. A combination of neural and biomechanical mechanisms associated with trunk control can explain the obtained model parameters. Future work will apply the gained insights in the design of movement-controlled neuroprostheses for facilitating trunk stability following spinal cord injury.

STUDY DESIGN Retrospective analysis. OBJECTIVE To describe the dynamic fluctuation of truncal shift parameters during quiet standing in healthy young individuals using biomechanical analyses. SUMMARY OF BACKGROUND DATA Coronal decompensation (CD) and sagittal vertical axis (SVA) are the key radiographic parameters to assess static truncal stability, with the known cut-off value of 4 cm for SVA in determining severity of spinal deformity. These values are obtained at a specific moment during quiet standing, when the posture innately changes. Thus, unassessed truncal sway could potentially compromise the reliability of these measurements. METHODS Previously obtained biomechanical data with 11 male, healthy participants aged 16 to 29 were used to quantify the dynamic sway of standing posture. The participants were instructed to quietly stand with surface reflective markers for 130 seconds. The midpoint of bilateral acromia was used as a surrogate for C7 vertebral body. The time series of coronal and sagittal shifts of C7 to sacrum were measured as quasi-coronal decompensation (CD) and quasi-sagittal vertical axis (SVA) to simulate CD and SVA on radiographs. A force platform was also used to measure the center of pressure (COP) displacement. RESULTS The group averages of the dynamic sway range were 20.2 ± 4.1 mm (range: 15.1-28.6) in the sagittal plane (quasi-SVA) and 9.8 ± 3.2 mm (range: 5.5-15.2) in the coronal plane (quasi-CD). There were significant correlations between quasi-CD sway and medial-lateral COP velocity (Pearson r = 0.65, P = 0.03), as well as between quasi-SVA sway and COP sway area (r = 0.65, P = 0.03). CONCLUSION Given the considerable fluctuation of quasi-SVA and quasi-CD during quiet standing, the reliability of radiographic measurement using CD and SVA at a specific moment can be substantially compromised. The assessment based on the currently proposed cut-off values should be interpreted with caution, and repeat examinations are warranted. LEVEL OF EVIDENCE 4.

Spinal cord injury (SCI) can result in paralysis of trunk muscles, which can affect sitting balance. The objective of this study was to analyze trunk muscle coordination of individuals with thoracic SCI and compare it to able-body individuals. A total of 27 individuals were recruited and subdivided into: (a) high thoracic SCI; (b) low thoracic SCI; and (c) able-body groups. Participants were seated and asked to lean their trunk in eight directions while trunk muscle activity was recorded. Muscle coordination was assessed using the non-negative matrix factorization (NMF) method to extract muscle modules, which are the synergistic trunk muscle activations, and their directional activation patterns. Our results showed that individuals with SCI used less muscle modules, more co-contractions, and less directional tuning, compared to able-bodied people. These results suggest impaired and simplified muscle coordination due to the loss of supraspinal input after SCI. Observed variability in muscle coordination within SCI groups also suggests that other mechanisms such as spasticity and muscle stretch reflexes or individual factors such as experience and training contributed to the postural muscle synergies. Overall, muscle coordination deficits revealed impaired neuromuscular strategies which provide implications for rehabilitation of trunk muscles during sitting balance after SCI.

Balance training in the aquatic environment is often used in rehabilitation practice to improve static and dynamic balance. Although aquatic therapy is widely used in clinical practice, we still lack evidence on how immersion in water actually impacts postural control. We examined how postural sway measured using centre of pressure and trunk acceleration parameters are influenced by the aquatic environment along with the effects of visual information. Our results suggest that the aquatic environment increases postural instability, measured by the centre of pressure parameters in the time-domain. The mean velocity and area were more significantly affected when individuals stood with eyes closed in the aquatic environment. In addition, a more forward posture was assumed in water with eyes closed in comparison to standing on land. In water, the low frequencies of sway were more dominant compared to standing on dry land. Trunk acceleration differed in water and dry land only for the larger upper trunk acceleration in mediolateral direction during standing in water. This finding shows that the study participants potentially resorted to using their upper trunk to compensate for postural instability in mediolateral direction. Only the lower trunk seemed to change acceleration pattern in anteroposterior and mediolateral directions when the eyes were closed, and it did so depending on the environment conditions. The increased postural instability and the change in postural control strategies that the aquatic environment offers may be a beneficial stimulus for improving balance control.

Introduction Transcutaneous neuromuscular electrical stimulation (NMES) can generate muscle contractions for rehabilitation and exercise. However, NMES-evoked contractions are limited by fatigue when they are delivered "conventionally" (CONV) using a single active electrode. Researchers have developed "sequential" (SEQ) stimulation, involving rotation of pulses between multiple "aggregated" (AGGR-SEQ) or "distributed" (DISTR-SEQ) active electrodes, to reduce fatigue (torque-decline) by reducing motor unit discharge rates. The primary objective was to compare fatigue-related outcomes, "potentiation," "variability," and "efficiency" between CONV, AGGR-SEQ, and DISTR-SEQ stimulation of knee extensors in healthy participants. Methods Torque and current were recorded during testing with fatiguing trains using each NMES type under isometric and isokinetic (180°/s) conditions. Results Compared with CONV stimulation, SEQ techniques reduced fatigue-related outcomes, increased potentiation, did not affect variability, and reduced efficiency. Conclusions SEQ techniques hold promise for reducing fatigue during NMES-based rehabilitation and exercise; however, optimization is required to improve efficiency. Muscle Nerve 56: 271-281, 2017.

Many individuals with lower limb amputations or neuromuscular impairments face mobility challenges attributable to suboptimal assistive device design. Forward dynamic modeling and simulation of human walking using conventional biomechanical gait models offer an alternative to intuition-based assistive device design, providing insight into the biomechanics underlying pathological gait. Musculoskeletal models enable better understanding of prosthesis and/or exoskeleton contributions to the human musculoskeletal system, and device and user contributions to both body support and propulsion during gait. This paper reviews current literature that have used forward dynamic simulation of clinical population musculoskeletal models to perform assistive device design optimization using optimal control, optimal tracking, computed muscle control (CMC) and reflex-based control. Musculoskeletal model complexity and assumptions inhibit forward dynamic musculoskeletal modeling in its current state, hindering computational assistive device design optimization. Future recommendations include validating musculoskeletal models and resultant assistive device designs, developing less computationally expensive forward dynamic musculoskeletal modeling methods, and developing more efficient patient-specific musculoskeletal model generation methods to enable personalized assistive device optimization.

Context/Objective: Incomplete spinal cord injury (iSCI) causes deficits in balance control. The Mini-Balance Evaluation Systems Test (mini-BESTest) is a comprehensive measure; however, further testing of its psychometric properties among the iSCI population is needed. We evaluated the mini-BESTest’s test-retest reliability, and concurrent and convergent validity among individuals living with iSCI for more than one year. Design: Cross-sectional study. Setting: Rehabilitation hospital. Participants: Twenty-one individuals with chronic motor iSCI (14 females, mean age 56.8 ± 14.0 years). Interventions: None. Outcome Measures: Participants completed the mini-BESTest at two sessions spaced two weeks apart. At the second session, participants performed tests of lower extremity muscle strength and quiet standing on a force platform with eyes opened (EO) and eyes closed (EC). Intraclass correlation coefficients (ICC) evaluated test-retest reliability. To evaluate concurrent and convergent validity, Pearson’s correlation coefficient (r) quantified relationships between mini-BESTest scores and measures of center of pressure (COP) velocity during EO and EC standing, and lower extremity muscle strength, respectively. Results: Test-retest reliability of the mini-BESTest total score and sub-scale scores were high (ICC = 0.94–0.98). Mini-BESTest scores were inversely correlated with COP velocity when standing with EO (r = 0.54–0.71, P

Neuromuscular electrical stimulation is conventionally applied through a single pair of electrodes over the muscle belly, denominated single electrode stimulation (SES). SES is limited by discomfort and incomplete motor-unit recruitment, restricting electrically-evoked torque and promoting premature fatigue-induced torque-decline. Sequential stimulation involving rotation of pulses between multiple pairs of electrodes has been proposed as an alternative, denominated spatially distributed sequential stimulation (SDSS). The present aim was to compare discomfort, maximal-tolerated torque, and fatigue-related outcomes between SES and SDSS of tibialis anterior. Ten healthy participants completed two experimental sessions. The self-reported discomfort at sub-maximal torque, the maximal-tolerated torque, fatigue-induced torque-decline during, and doublet-twitch torque at 10- and 100-Hz before and after, 300 intermittent (0.6-s-ON-0.6-s-OFF) isokinetic contractions were compared between SES and SDSS. SDSS stimulation improved fatigue-related outcomes, whereas increased discomfort and reduced maximal-tolerated torque. SDSS holds promise for reducing fatigue. However, limited torque production and associated discomfort may limit its utility for rehabilitation/training.

STUDY DESIGN: Case series. OBJECTIVES: This case series describes how the aquatic environment influences gait initiation in terms of the center of pressure (COP) excursion, impulses, trunk acceleration, and perceptions of participants with incomplete spinal cord injury (iSCI). SETTING: Tertiary Rehabilitation Hospital, Ontario, Canada. METHODS: Five individuals with iSCI (four cervical injuries/one thoracic injury, AIS D) participated in the study. Baseline clinical balance was evaluated by Berg Balance Scale and Mini-Balance Evaluation System Test. Participants initiated gait on a waterproof force plate and walked ~4 steps, in water and on land. COP trajectories during anticipatory and execution phases, impulses, and trunk acceleration parameters were investigated. Perceptions of walking in both environments were obtained using an interview. RESULTS: COP trajectory was prominently longer when individuals stepped forward. A decrease in velocity of COP was observed predominantly in the AP direction during stepping. Non-normalized vertical impulses decreased as the AP impulses increased, in water compared to land. Upper to lower trunk acceleration ratios showed how water resistance influenced the lower trunk acceleration. Most of participants reported that walking in water was challenging, but safer than on land. CONCLUSIONS: Participants with higher balance function seemed to have more pronounced changes in anticipatory and execution phases’ duration, length and velocity of COP. A faster anticipatory phase and a slower execution phase were observed in water than on land. Participants walked in water using a different trunk control strategy than on land and reported no fear of falling when walking in water versus land.

Cross sectional. To compare the reactive stepping ability of individuals living with incomplete spinal cord injury or disease (SCI/D) to that of sex- and age-matched able-bodied adults. A tertiary SCI/D rehabilitation center in Canada. Thirty-three individuals (20 with incomplete SCI/D) participated. Participants assumed a forward lean position in standing whilst 8–12% of their body weight was supported by a horizontal cable at waist height affixed to a rigid structure. The cable was released unexpectedly, simulating a forward fall and eliciting one or more reactive steps. Behavioral responses (i.e., single step versus non-single step) were compared using a Chi-square test. The following temporal parameters of reactive stepping were compared using t-tests: the onset of muscle activation in 12 lower extremity muscles (six per limb) and step-off, step contact and swing time of the stepping leg. Behavioral responses were significantly different between groups (χ2 = 13.9 and p

Made available in DSpace on 2022-04-30T20:25:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-01 Ontario Neurotrauma Foundation Natural Sciences and Engineering Research Council of Canada Canadian Institutes of Health Research Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung Study design: This work is a case series. Objectives: We assessed the influence of the aquatic environment on quasi-static posture by measuring center of pressure (COP) sway and trunk acceleration parameters after incomplete spinal cord injury (iSCI) in water and on land. Setting: Tertiary Rehabilitation Hospital, Ontario, Canada. Methods: Six adult participants with iSCI (4 cervical/2 thoracic injuries, AIS D) were enrolled. Baseline balance was assessed by the Berg Balance Scale and Mini-Balance Evaluation System Test. Participants stood on a waterproof force plate for one minute per trial on land and in water; participants completed testing with their eyes open or closed in random order over 10 trials. Individuals’ perceptions of their standing balance were obtained. COP and trunk acceleration parameters were analyzed in the time-domain. Results: COP sway and upper to lower trunk acceleration ratios in the AP direction increased in water, which was in contrast to standing on land in both visual conditions for 5/6 participants. Three participants (P1, P3 & P4) with greater sensorimotor deficits had larger COP sway in water with the eyes closed. Two (P1 & P4) of six participants reported more discomfort standing in water than standing on land. Conclusions: Increased COP sway seemed to reflect the balance and sensorimotor impairments of the participants, especially when standing with eyes closed in water. Although most participants (4/6) perceived that they swayed more in water in contrast to on land, 5 out of 6 participants reported that water felt like a safer environment in which to stand. Toronto Rehabilitation Institute – University Health Network Rehabilitation Sciences Institute – University of Toronto Department of Mechanical Engineering University of Alberta Department of Medicine Rehabilitation Sciences Institute – University of Toronto Institute of Biomaterials and Biomedical Engineering University of Toronto Institute of Biosciences – Sao Paulo State University Institute of Biomaterials and Biomedical Engineering Rehabilitation Sciences Institute – University of Toronto Department of Physical Therapy Rehabilitation Sciences Institute Institute of Medical Science University of Toronto Institute of Biosciences – Sao Paulo State University Natural Sciences and Engineering Research Council of Canada: 249669 Canadian Institutes of Health Research: 95662 Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung: P300P2-147865

Trunk muscles are responsible for maintaining trunk stability during sitting. However, the effects of anticipation of perturbation on trunk muscle responses are not well understood. The objectives of this study were to identify the responses of trunk muscles to sudden support surface translations and quantify the effects of anticipation of direction and time of perturbation on the trunk neuromuscular responses. Twelve able-bodied individuals participated in the study. Participants were seated on a kneeling chair and support surface translations were applied in the forward and backward directions with and without direction and time of perturbation cues. The trunk started moving on average approximately 40ms after the perturbation. During unanticipated perturbations, average latencies of the trunk muscle contractions were in the range between 103.4 and 117.4ms. When participants anticipated the perturbations, trunk muscle latencies were reduced by 16.8±10.0ms and the time it took the trunk to reach maximum velocity was also reduced, suggesting a biomechanical advantage caused by faster muscle responses. These results suggested that trunk muscles have medium latency responses and use reflexive mechanisms. Moreover, anticipation of perturbation decreased trunk muscles latencies, suggesting that the central nervous system modulated readiness of the trunk based on anticipatory information.

We investigated age-related differences in the required coefficient of friction (RCOF) during 90° turning, the difference of RCOF during step and spin turn, and how affects observed differences. Sixteen healthy young and healthy older adults (eight men and eight women in each group) participated. Participants performed 90° step and spin turns to the right at a self-selected normal speed. Older adults turned with lower RCOF than the young adults during both step and spin turns. This was associated with reduced mediolateral (ML) RCOF component (RCOFML) for the older adults. Reduced RCOFML in older adults was associated with reductions in the ML component of the lean angle of the body during turning. This age-related gait changes during turning can be compensatory mechanisms that allowed older adults to turn while reducing the risk of slipping. Spin turns exhibited lower RCOF, resulting from significantly lower RCOFML, than step turns in young and older adults; thus, spin turning is a safer turning strategy for preventing lateral slips. This may suggest that, in older adults, slip prevention may take precedence over balance recovery after slips sustained during turning. These results illustrate a turning gait mechanism that helps prevent slips and falls, and how age affects this mechanism.

Background Individuals with cervical spinal cord injury usually sustain impairments to the trunk and upper and lower limbs, resulting in compromised sitting balance. The objectives of this study were to: 1) compare postural control of individuals with cervical spinal cord injury and able-bodied individuals; and 2) investigate the effects of foot support and trunk fluctuations on postural control during sitting balance. Methods Ten able-bodied individuals and six individuals with cervical spinal cord injury were asked to sit quietly during two 60 s trials. The forces exerted on the seat and the foot support surfaces were measured separately using two force plates. The global centre of pressure sway was obtained from the measurements on the two force plates, and the sway for each force plate was calculated individually. Findings Individuals with spinal cord injury had at least twice as large global and seat sways compared to able-bodied individuals, while foot support sway was not significantly different between the two groups. Comparison between global and seat sways showed that anterior–posterior velocity of global sway was larger compared to the seat sway in both groups. Interpretation Postural control of individuals with cervical spinal cord injury was worse than that of able-bodied individuals. The trunk swayed more in individuals with spinal cord injury, while the stabilization effect of the feet did not differ between the groups. Foot support affected anterior–posterior fluctuations in both groups equally. Thus, trunk control is the dominant mechanism contributing to sitting balance in both able-bodied and spinal cord injury individuals.

Increased variability of spatio-temporal features while walking is related to increased risk of falls. It is thought that variability in foot placement and timing reflects responses to mechanical instability while walking. The purpose of this study was to determine whether ‘extreme’ values of step length, width and time follow transient periods of low mechanical stability during the single support phase of gait in healthy young adults. We conducted secondary analysis of a portion of an existing dataset. Eleven healthy adults walked on an instrumented treadmill. Participants were outfitted with reflective markers and completed two 1-minute periods of walking at each of 3 speeds (0.8 m/s, 1.2 m/s, and 1.6 m/s). Margins of stability were calculated relative to the anterior, posterior, lateral, and medial boundaries of the base of support, and the value at heel strike and the minimum value during the first half of each single-support phase were extracted. Step length, swing time, and step width were calculated from motion capture and ground reaction force data. Extreme values for consecutive steps were identified using Poincaré plots, and margins of stability in each direction were compared between ‘normal’ and ‘extreme’ steps. Margins of stability in both the anterior and medial direction were lower prior to long and wide steps, respectively. Margins of stability in the anterior and medial directions were lower prior to quick steps, and margins of stability in the posterior and lateral directions were lower prior to slow steps. There were either no significant differences in margin of stability between ‘normal’ and ‘extreme’ steps at heel strike, or the direction of the relationship was reversed to that observed during single support. These data suggest that spatio-temporal variability may reflect adjustments in step placement and timing to compensate for transient periods of low mechanical stability when walking.

The precise role of the human primary motor cortex in walking is unknown. Our previous study showed that the primary motor cortex may contribute to specific requirements of walking (i.e., maintaining a constant movement frequency and bilaterally coordinating the feet). Because aging can impair (i) the ability to fulfill the aforementioned requirements and (ii) corticomuscular communication, we hypothesized that aging would impair the motoneuronal recruitment by the primary motor cortex during bilateral cyclical movements. Here, we used corticomuscular coherence (i.e., coherence between the primary motor cortex and the active muscles) to examine whether corticomuscular communication is affected in older individuals during cyclical movements that shared some functional requirements with walking. Fifteen young men and 9 older men performed cyclical, anti-phasic dorsiflexion and plantarflexion of the feet while seated. Coherence between the midline primary motor cortex and contracting leg muscles cyclically increased in both age groups. However, the coherence of older participants was characterized by (i) lower magnitude and (ii) mediolaterally broader and more rostrally centered cortical distributions. These characteristics suggest that aging changes how the primary motor cortex participates in the cyclical movements, and such change may extend to walking.

Multi-channel surface functional electrical stimulation (FES) for walking has been used to improve voluntary walking and balance in individuals with spinal cord injury (SCI).To investigate short- and long-term benefits of 16 weeks of thrice-weekly FES-assisted walking program, while ambulating on a body weight support treadmill and harness system, versus a non-FES exercise program, on improvements in gait and balance in individuals with chronic incomplete traumatic SCI, in a randomized controlled trial design.Individuals with traumatic and chronic (≥18 months) motor incomplete SCI (level C2 to T12, American Spinal Cord Injury Association Impairment Scale C or D) were recruited from an outpatient SCI rehabilitation hospital, and randomized to FES-assisted walking therapy (intervention group) or aerobic and resistance training program (control group). Outcomes were assessed at baseline, and after 4, 6, and 12 months. Gait, balance, spasticity, and functional measures were collected.Spinal cord independence measure (SCIM) mobility sub-score improved over time in the intervention group compared with the control group (baseline/12 months: 17.27/21.33 vs. 19.09/17.36, respectively). On all other outcome measures the intervention and control groups had similar improvements. Irrespective of group allocation walking speed, endurance, and balance during ambulation all improved upon completion of therapy, and majority of participants retained these gains at long-term follow-ups.Task-oriented training improves walking ability in individuals with incomplete SCI, even in the chronic stage. Further randomized controlled trials, involving a large number of participants are needed, to verify if FES-assisted treadmill training is superior to aerobic and strength training.

Traumatic spinal cord injury (SCI) results in substantial reductions in lower extremity muscle mass and bone mineral density below the level of the lesion. Whole-body vibration (WBV) has been proposed as a means of counteracting or treating musculoskeletal degradation after chronic motor complete SCI. To ascertain how WBV might be used to augment muscle and bone mass, we investigated whether WBV could evoke lower extremity electromyography (EMG) activity in able-bodied individuals and individuals with SCI, and which vibration parameters produced the largest magnitude of effect.Ten male subjects participated in the study, six able-bodied and four with chronic SCI. Two different manufacturers' vibration platforms (WAVE(®) and Juvent™) were evaluated. The effects of vibration amplitude (0.2, 0.6 or 1.2 mm), vibration frequency (25, 35, or 45 Hz), and subject posture (knee angle of 140°, 160°, or 180°) on lower extremity EMG activation were determined (not all combinations of parameters were possible on both platforms). A novel signal processing technique was proposed to estimate the power of the EMG waveform while minimizing interference and artifacts from the plate vibration.WBV can elicit EMG activity among subjects with chronic SCI, if appropriate vibration parameters are employed. The amplitude of vibration had the greatest influence on EMG activation, while the frequency of vibration had lesser but statistically significant impact on the measured lower extremity EMG activity.These findings suggest that WBV with appropriate parameters may constitute a promising intervention to treat musculoskeletal degradation after chronic SCI.

Trunk instability during sitting is a major problem following neuromuscular injuries such as stroke and spinal cord injury. In order to develop new strategies for alleviating this problem, a better understanding of the intrinsic contributions of the healthy trunk to sitting control is needed. As such, this study set out to propose and validate a novel methodology for determining multidirectional trunk stiffness during sitting using randomized transient perturbations. Fifteen healthy individuals sitting naturally on a custom-made seat were randomly perturbed in eight horizontal directions. Trunk stiffness and damping were quantified using force and trunk kinematics in combination with translational and torsional models of a mass-spring-damper system. The results indicate that stiffness and damping of the healthy trunk are roughly symmetrical between the two body sides. Moreover, both quantities are smallest in the anterior and largest in the lateral directions. In conclusion, a novel protocol for identifying intrinsic trunk stiffness and damping has been developed, eliminating anticipation effects with respect to perturbation timing and direction. Subsequent studies will use these findings as a reference not only for quantifying trunk stiffness and damping in individuals with various neuromuscular disorders, but also for assessing whether neuroprostheses could increase upper body stiffness and, hence, stability.

In this pilot study, we examined how effectively functional electrical stimulation (FES) and passive stepping mitigated orthostatic hypotension in participants with chronic spinal cord injury (SCI). While being tilted head-up to 70 (°) from the supine position, the participants underwent four 10-min conditions in a random sequence: 1) no intervention, 2) passive stepping, 3) isometric FES of leg muscles, and 4) FES of leg muscles combined with passive stepping. We found that FES and passive stepping independently mitigated a decrease in stroke volume and helped to maintain the mean blood pressure. The effects of FES on stroke volume and mean blood pressure were greater than those of passive stepping. When combined, FES and passive stepping did not interfere with each other, but they also did not synergistically increase stroke volume or mean blood pressure. Thus, the present study suggests that FES delivered to lower limbs can be used in individuals with SCI to help them withstand orthostatic stress. Additional studies are needed to confirm whether this use of FES is applicable to a larger population of individuals with SCI.

Gait initiation is defined as the transition from stationary standing to steady-state walking. Despite the frequent use of therapy pools for training walking in early stages of rehabilitation, none have been reported on the effects of immersion on gait initiation. We aimed to analyze the center of pressure (COP) trajectories, the vertical and anteroposterior impulses and upper and lower trunk accelerations during anticipatory (APA) and execution phases of gait initiation. In the COP trajectory, the execution (EXE) phase was further subdivided in two phases: predominantly mediolateral (EXE1), and predominantly anteroposterior (EXE2). Able-bodied participants initiated gait while standing on a force plate and walked approximately 4 steps following a visual cue. The participants were wearing three inertial sensors placed on the lower and upper trunk, and on the stance shank. Individuals performed 10 trials each on land and in water, in two consecutive days. The lengths and velocities of COP trajectories increased in water compared to land during APA, while the COP length increased and the COP velocity reduced in water during EXE2. The anteroposterior impulses increased in water during EXE. Lower trunk acceleration was smaller in water while the upper trunk acceleration did not differ, resulting in the larger ratio of upper to lower trunk acceleration in water during EXE. Overall, immersion in water increases COP length during gait initiation, and reduces COP velocity during EXE2, indicating a new postural strategy in water. The aquatic medium may be favorable for individuals who need weight support, gradual resistance and a longer time to execute gait initiation.

It has been reported that the elderly use co-contraction of the tibialis anterior (TA) and plantarflexor muscles for longer duration during quiet standing than the young. However, the particular role of ankle muscle co-contractions in the elderly during quiet standing remains unclear. Therefore, the objective of this study was to investigate the association between ankle muscle co-contractions and postural steadiness during standing in the elderly. Twenty-seven young (27.2±4.5yrs) and twenty-three elderly (66.2±5.0yrs) subjects were asked to stand quietly on a force plate for five trials. The center of pressure (COP) trajectory and its velocity (COPv) as well as the center of mass (COM) trajectory and its velocity (COMv) and acceleration (ACC) were calculated using the force plate outputs. Electromyograms were obtained from the right TA, soleus (SOL), and medial gastrocnemius (MG) muscles. Periods of TA activity (TAon) and inactivity (TAoff) were determined using an EMG threshold based on TA resting level. Our results indicate that, in the elderly, the COPv, COMv, and ACC variability were significantly larger during TAon periods compared to TAoff periods. However, in the young, no significant association between respective variability and TA activity was found. We conclude that ankle muscle co-contractions in the elderly are not associated with an increase, but a decrease in postural steadiness. Future studies are needed to clarify the causal relationship between (1) ankle muscle co-contractions and (2) joint stiffness and multi-segmental actions during standing as well as their changes with aging.

Background To date, few pharmacologic or rehabilitation interventions for sublesional osteoporosis (SLOP) or low bone mass of the hip and knee regions after spinal cord injury (SCI) have produced significant or sustained increases in lower extremity bone mineral density. Whole body vibration (WBV) is a potential intervention for the prevention and/or treatment of SLOP. Objective To identify the optimal WBV conditions (ie, plate, frequency, amplitude, and subject posture) among men with chronic SCI during passive standing and facilitate the implementation and future evaluation of the efficacy of WBV and passive standing for prevention and treatment of SLOP in men with SCI. Design This phase 0 device development study assessed the lower extremity propagation characteristics of WBV in men with and without SCI by using a variety of a priori specified plates, frequencies, amplitudes, and postures that facilitate lower extremity vibration absorption while minimizing vibration propagation to the head. Setting A tertiary SCI rehabilitation center in Toronto, Canada. Participants Healthy men with chronic paraplegia (n = 5) and those without SCI (n = 7), ages 20-50 years, weight 68-113 kg, and height 168-188 cm. Interventions An EasyStand standing frame (Altimate Medical Inc, Morton, MN) was fitted onto 2 commercially available vibration platforms: WAVE (WAVE Manufacturing Inc, Windsor, Ontario, Canada) and Juvent (Juvent Medical Inc, Somerset, NJ). Accelerometers were attached to the participants' forehead, hip, knee, and ankle to measure vibration propagation. Vibration parameters evaluated were posture (knee angles of 140°, 160°, and 180° [180° for Juvent only]), vibration frequency (25 Hz, 35 Hz, and 45 Hz), and vibration amplitude (0.6 mm and 1.2 mm [WAVE only]). The subjects were exposed to all combinations of posture, frequencies, and amplitudes during the experiments (total parameter combinations: 12 WAVE and 9 Juvent). Main Outcome Measurements Peak-to-peak vibration and transmissibility of vibration were recorded and computed for each accelerometer at the tested locations. Results Variations in frequency generated the most noticeable changes in propagation characteristics, followed by variations in knee angle and amplitude. Conclusions WBV therapy delivered with use of the WAVE platform with a knee angle of 140°, plate frequency of 45 Hz, and amplitude of 1.2 mm met our a priori criteria for the "optimal WBV condition." Future studies should evaluate the therapeutic efficacy of the WAVE platform by using these parameters to maintain or augment bone mass among persons with SCI and SLOP.

Seated postural stability has not been studied extensively in individuals with spinal cord injury (SCI). The main purpose of this study was to compare the effects of upper limb (U/L) positions and U/L weight support roles on quasi-static postural stability between individuals with SCI and healthy controls. Fourteen individuals with SCI and 14 healthy controls sat on an instrumented seat with their feet resting on force plates and randomly maintained five short-sitting positions for 60s with or without hand support. Center-of-pressure (COP) measures based on displacement and frequency series were computed. Individuals with SCI exhibited greater mean COP displacement and velocity measures compared to healthy controls, as well as lower COP frequency measures, irrespective of the U/L positions and weight support roles, confirming reduced stability and a difference in preferential postural regulation strategies. The use of U/L support is a compensatory strategy that influences seated stability in individuals with SCI.

Purpose. To determine the feasibility of increasing the cardiopulmonary exercise intensity during walking with gait-patterned functional electrical stimulation (GP-FES) among individuals with motor incomplete SCI. Methods. Two men with motor-incomplete SCI (Subjects A and B, age 45 and 50 years; Level of Injury: C4 and T10; AIS score: D and D, resp.) performed a three sequential four-minute continuous walking sessions [(1) regular gait (non-GP-FES-1); (2) gait with GP-FES (GP-FES); (3) regular gait (non-GP-FES-2)]. Oxygen consumption (Vo2) was measured continuously during trials. Results. Vo2 was higher during GP-FES (Subjects A and B; 14.5 and 19.1 mL/kg/min, resp.) as compared to regular gait (Non-GP-FES-1: Subjects A and B; 13.4 and 17.0: mL/kg/min, resp.; non-GP-FES-2: Subjects A and B; 13.1 and 17.5: mL/kg/min, resp.). Conclusion. The exercise intensity of GP-FES walking was higher than that of regular walking among individuals with motor incomplete SCI. Further investigations are required to determine the clinical relevance of the exercise.

Purpose: It has been generally assumed that muscle volume is not a limiting factor of balance for young populations. To verify this assumption, this study investigated the relationship between postural stability and muscle volume of the plantar flexors, which have been regarded as the major agonist muscles for postural control, of healthy young male individuals. Methods: Forty-five healthy young males were requested to maintain quiet standing on a force platform for 60 s in eyes-open and eyes-closed conditions. Various time and frequency domain measures of the center of pressure were calculated. Muscle volume of the plantar flexors was estimated from muscle thickness in the lateral gastrocnemius and soleus muscles measured by ultrasonography and was divided by body mass to yield the normalized muscle volume. Results: Many time domain center of pressure measures such as mean distance, root mean square, and mean velocity were negatively correlated to normalized muscle volume (P < 0.05). Conclusions: It is suggested that, even among the young males, the muscle volume of their plantar flexors can act as a limiting factor for postural stability

Functional electrical stimulation (FES) is limited by the rapid onset of muscle fatigue caused by localized nerve excitation repeatedly activating only a subset of motor units. The purpose of this study was to investigate reducing fatigue by sequentially changing, pulse by pulse, the area of stimulation using multiple surface electrodes that cover the same area as one electrode during conventional stimulation. Paralyzed triceps surae muscles of an individual with complete spinal cord injury were stimulated, via the tibial nerve, through four active electrodes using spatially distributed sequential stimulation (SDSS) that was delivered by sending a stimulation pulse to each electrode one after another with 90° phase shift between successive electrodes. For comparison, single electrode stimulation was delivered through one active electrode. For both modes of stimulation, the resultant frequency to the muscle as a whole was 40 Hz. Isometric ankle torque was measured during fatiguing stimulations lasting 2 min. Each mode of stimulation was delivered a total of six times over 12 separate days. Three fatigue measures were used for comparison: fatigue index (final torque normalized to maximum torque), fatigue time (time for torque to drop by 3 dB), and torque-time integral (over the entire trial). The measures were all higher during SDSS (P < 0.001), by 234, 280, and 171%, respectively. The results are an encouraging first step toward addressing muscle fatigue, which is one of the greatest problems for FES.

Whole-body vibration (WBV) is being used to enhance neuromuscular performance including muscle strength, power, and endurance in many settings among diverse patient groups including elite athletes. However, the mechanisms underlying the observed neuromuscular effects of WBV have not been established. The extent to which WBV will produce similar neuromuscular effects among patients with neurological impairments unable to voluntarily contract their lower extremity muscles is unknown. We hypothesized that modulation of spinal motorneuronal excitability during WBV may be achieved without voluntary contraction. The purpose of our study was to describe and compare the acute effects of WBV during passive standing in a standing frame on the soleus H-reflex among men with and without spinal cord injury (SCI). In spinal cord intact participants, WBV caused significant inhibition of the H-reflex as early as 6s after vibration onset (9.0+/-3.9%) (p0.001). The magnitude of the H-reflex gradually recovered after WBV, but remained significantly below initial values until 36s post-WBV (57.5+/-22.0%) (p=0.01). Among participants with SCI, H-reflex inhibition was less pronounced with onset 24 s following WBV (54.2+/-18.7%) (p=0.03). The magnitude of the H-reflex fully recovered after 60s of WBV exposure. These results concur with prior reports of inhibitory effects of local vibration application on the H-reflex. Our results suggest that acute modulation of spinal motoneuronal excitability during WBV can be achieved in the absence of voluntary leg muscle contractions. Nonetheless, WBV has implications for rehabilitation service delivery through modulation of spinal motoneuronal excitability in individuals with SCI.

Body fluctuations during both quiet standing and walking exhibit temporal correlations that reflect mechanisms of balance control. However, knowledge about the relationship between the temporal structures observed during standing and walking is limited. The goal of the present study was (1) to investigate temporal correlations in the fluctuations of the center of body mass acceleration (ACC) in standing and walking, and (2) to test the hypothesis that the degree of the temporal correlation for the two tasks is similar and correlated across participants. Seventeen young, healthy participants stood and walked for 10 min on a treadmill equipped with two force platforms. The temporal correlations of the ACC in the anteroposterior (ACC(AP)), mediolateral (ACC(ML)), and two-dimensional (ACC(2D)) directions were evaluated using the scaling index (alpha) as calculated with Detrended Fluctuation Analysis. The scaling indices of ACC fluctuations during standing and walking were categorized as stationary signals which are temporally correlated (0.5

Parkinson's disease (PD) is known to increase asymmetry and variability of bilateral movements. However, the mechanisms of such abnormalities are not fully understood. Here, we aimed to investigate whether kinematic abnormalities are related to cortical participation during bilateral, cyclical ankle movements, which required i) maintenance of a specific frequency and ii) bilateral coordination of the lower limbs in an anti-phasic manner. We analyzed electroencephalographic and electromyographic signals from nine men with PD and nine aged-matched healthy men while they sat and cyclically dorsi- and plantarflexed their feet. This movement was performed at a similar cadence to normal walking under two conditions: i) self-paced and ii) externally paced by a metronome. Participants with PD exhibited reduced range of motion and more variable bilateral coordination. However, participants with and without PD did not differ in the magnitude of corticomuscular coherence between the midline cortical areas and tibialis anterior and medial gastrocnemius muscles. This finding suggests that either the kinematic abnormalities were related to processes outside linear corticomuscular communication or PD-related changes in neural correlates maintained corticomuscular communication but not motor performance.

The majority of individuals with a spinal cord injury experience sensory and motor trunk impairments. The severity of these impairments, along with their side effects on postural stability and upper limb strengthgenerating capability, may reduce these individuals’ capacity to efficiently propel their manual wheelchair and perform other wheelchair-related activities. This article presents a brief overview of the relevant literature focusing on potential effects of trunk impairments on manual wheelchair propulsion and explores a few future research challenges. There is a need to develop quantitative sensorimotor trunk assessment and to develop innovative therapeutic approaches.