Nondisabled Volunteers Research Articles

Center of Mass Estimation for Impaired Gait Assessment Using Inertial Measurement Units.

Injury or disease often compromise walking dynamics and negatively impact quality of life and independence. Assessing methods to restore or improve pathological gait can be expedited by examining a global parameter that reflects overall musculoskeletal control. Center of mass (CoM) kinematics follow well-defined trajectories during unimpaired gait, and change predictably with various gait pathologies. We propose a method to estimate CoM trajectories from inertial measurement units (IMUs) using a bidirectional Long Short-Term Memory neural network to evaluate rehabilitation interventions and outcomes. Five non-disabled volunteers participated in a single session of various dynamic walking trials with IMUs mounted on various body segments. A neural network trained with data from four of the five volunteers through a leave-one-subject out cross validation estimated the CoM with average root mean square errors (RMSEs) of 1.44cm, 1.15cm, and 0.40cm in the mediolateral (ML), anteroposterior (AP), and inferior/superior (IS) directions respectively. The impact of number and location of IMUs on network prediction accuracy was determined via principal component analysis. Comparing across all configurations, three to five IMUs located on the legs and medial trunk were the most promising reduced sensor sets for achieving CoM estimates suitable for outcome assessment. Lastly, the networks were tested on data from an individual with hemiparesis with the greatest error increase in the ML direction, which could stem from asymmetric gait. These results provide a framework for assessing gait deviations after disease or injury and evaluating rehabilitation interventions intended to normalize gait pathologies.

Validation of wearable inertial sensor-based gait analysis system for measurement of spatiotemporal parameters and lower extremity joint kinematics in sagittal plane.

Wearable inertial sensor-based motion analysis systems are promising alternatives to standard camera-based motion capture systems for the measurement of gait parameters and joint kinematics. These wearable sensors, unlike camera-based gold standard systems, find usefulness in outdoor natural environment along with confined indoor laboratory-based environment due to miniature size and wireless data transmission. This study reports validation of our developed (i-Sens) wearable motion analysis system against standard motion capture system. Gait analysis was performed at self-selected speed on non-disabled volunteers in indoor (n = 15) and outdoor (n = 8) environments. Two i-Sens units were placed at the level of knee and hip along with passive markers (for indoor study only) for simultaneous 3D motion capture using a motion capture system. Mean absolute percentage error (MAPE) was computed for spatiotemporal parameters from the i-Sens system versus the motion capture system as a true reference. Mean and standard deviation of kinematic data for a gait cycle were plotted for both systems against normative data. Joint kinematics data were analyzed to compute the root mean squared error (RMSE) and Pearson's correlation coefficient. Kinematic plots indicate a high degree of accuracy of the i-Sens system with the reference system. Excellent positive correlation was observed between the two systems in terms of hip and knee joint angles (Indoor: hip 3.98° ± 1.03°, knee 6.48° ± 1.91°, Outdoor: hip 3.94° ± 0.78°, knee 5.82° ± 0.99°) with low RMSE. Reliability characteristics (defined using standard statistical thresholds of MAPE) of stride length, cadence, walking speed in both outdoor and indoor environment were well within the "Good" category. The i-Sens system has emerged as a potentially cost-effective, valid, accurate, and reliable alternative to expensive, standard motion capture systems for gait analysis. Further clinical trials using the i-Sens system are warranted on participants across different age groups.

Spatio-temporal parameters and intralimb coordination patterns describing hemiparetic locomotion at controlled speed

BackgroundComparison between healthy and hemiparetic gait is usually carried out while subjects walk overground at preferred speed. This generates bias due to the lack of uniformity across selected speeds because they reflect the great variability of the functional level of post-stroke patients. This study aimed at examining coordinative adaptations during walking in response to unilateral brain damage, while homologous participants walked at two fixed speeds.MethodsFive patients with left and five with right chronic hemiparesis, characterized by similar level of motor functioning, were enrolled. Ten non-disabled volunteers were recruited as matched control group. Spatio-temporal parameters, and intralimb thigh-leg and leg-foot coordination patterns were used to compare groups while walking on a treadmill at 0.4 and 0.6 m/s. The likelihood of Continuous Relative Phase patterns between healthy and hemiparetic subjects was evaluated by means of the root mean square of the difference and the cross correlation coefficient. The effects of the group (i.e., healthy vs. hemiparetics), side (i.e., affected vs.unaffected), and speed (e.g., slow vs. fast) were analyzed on all metrics using the Analysis of Variance.ResultsSpatio-temporal parameters of all hemiparetic subjects did not significantly differ from those of healthy subjects nor showed any asymmetry between affected and unaffected limbs. Conversely, both thigh-leg and foot-leg coordination patterns appeared to account for pathology related modifications.ConclusionComparisons between hemiparetic and healthy gait should be carried out when all participants are asked to seek the same suitable dynamic equilibrium led by the same external (i.e., the speed) and internal (i.e., severity of the pathology) conditions. In this respect, biomechanical adaptations reflecting the pathology can be better highlighted by coordinative patterns of coupled segments within each limb than by the spatio-temporal parameters. Accordingly, a deep analysis of the intralimb coordination may be helpful for clinicians while designing therapeutic treatments.

In vivo trial results of a novel ultrasonic cough stimulator

The aims of these double-blind in-vivo trials of a prototype ultrasonic cough stimulator (CoughStim™) were to establish (1) whether ultrasound (US) stimulation can be safely used to stimulate a cough, (2) the most efficient US frequency and power parameters to reliably stimulate a cough, (3) whether single- or dual-sided stimulation is more effective, and (4) whether a cough can be stimulated in adults unable to cough on demand. Fifteen nondisabled volunteers (18-59 yr) and seven volunteers unable to cough on demand (85-102 yr) were recruited. Stimulation was applied to the neck unilaterally at eight frequencies and two power levels and bilaterally at two frequencies and three power levels. Vital signs were monitored during testing with no adverse responses. CoughStim stimulated a cough in all nondisabled subjects, 80% of subjects at 0.58 MHz and 9 W unilaterally and 75% of subjects at 0.58 MHz and 6 W bilaterally. Of the subjects unable to cough, 71 percent responded to bilateral stimuli (0.54 MHz and 6 W) with a strong cough. The CoughStim regularly and safely produced a moderately strong cough response in subjects with or without ability to cough and produced this effect without causing undue discomfort.

An objective method for selecting command sources for myoelectrically triggered lower-limb neuroprostheses

Functional electrical stimulation (FES) facilitates ambulatory function after paralysis of persons with spinal cord injury (SCI) by exciting the peripheral motor nerves to activate the muscles of the lower limbs. This study identified a process for selecting command sources for triggering FES with the surface electromyogram (EMG) from muscles partially paralyzed by incomplete SCI, given its high degree of intersubject variability. We found Discriminability Index (DI) to be a good metric to evaluate the potential of controlling FES-assisted ambulation in four nondisabled volunteers and two participants with incomplete paralysis. The left erector spinae (ES) (mean DI = 0.87) for triggering the left step and the right ES (mean DI = 0.83) for triggering the right step were the best command sources for participant 1. The left ES (mean DI = 0.93) for triggering the left step and the right medial gastrocnemius (mean DI = 0.88) for triggering the right step were the best command sources for participant 2. Our results showed that command sources can be selected objectively from surface EMG before a fully implantable EMG-triggered FES system for walking is implemented.

Rectification of legibility distance in a driving simulator

Visual differences lead to differences in the legibility distances of traffic signs between driving simulators and real road environments. To ensure that the legibility distance in a simulator is similar to that in the real world, this study proposes a theoretical equation for predicting legibility distance and a simple algorithm for determining the magnifying power of a traffic sign for a display system in a simulator. Experiments of traffic sign recognition using a simulator were conducted under quasi-static and dynamic driving conditions. On-road tests were also carried out under quasi-static and dynamic driving conditions. Thirty healthy and non-disabled volunteers were recruited. The experimental results showed that the proposed theoretical equation for predicting legibility distance and the simple algorithm for determining the magnifying power of traffic signs reduced the difference in legibility distances between the simulator and real road environment under quasi-static and dynamic driving conditions.

Effect of temperature on electrophysiological parameters of swallowing

The effect of three different temperature ranges on the triggering of voluntary-induced swallowing and on the duration of the pharyngeal phase of oropharyngeal swallowing was studied electrophysiologically. The relationship between volume and temperature of liquids swallowed was also explored. This study included 40 nondisabled volunteers (23 male and 17 female). Laryngeal vertical movements and submental electromyographic activity were recorded as each subject swallowed water at three different temperature ranges: normal (23-25 degrees C), cold (8-10 degrees C), and hot (58-60 degrees C). The time for triggering of the pharyngeal phase of swallowing was found to be shorter for cold and hot water than for normal temperature water (p < 0.01). The duration of the pharyngeal phase of oropharyngeal swallowing was also shorter for cold and hot water than for normal temperature water (p < 0.05). The maximum capacity of a single bolus (dysphagia limit) was >20 mL of water in all nondisabled subjects for different temperatures. However, the capacity was significantly less for hot water relative to normal temperature water and cold water (p < 0.05). In conclusion, the temperature ranges used in this study were found to be effective in triggering voluntary-induced swallowing.

Pressure changes under the ischial tuberosities of seated individuals during sacral nerve root stimulation

Neuromuscular stimulation via the sacral nerve roots is proposed for prevention of ischial pressure ulcers following a spinal cord injury (SCI). Acute effects of sacral functional magnetic stimulation (FMS) on seat interface pressure changes were investigated in five nondisabled volunteers. Similar effects were demonstrated with functional electrical stimulation in people with SCI who used a sacral anterior root stimulator implant. The results indicated that sacral nerve root stimulation, either by FMS or implanted electrical stimulation, induced gluteus maximus contraction and mild pelvic tilt sufficient for clinically significant reductions in ischial pressures during sitting.

Temporospatial and kinematic gait alterations during treadmill walking with body weight suspension.

Our purpose was to analyze the effects of selected levels of body weight support (BWS) on lower extremity kinematics of normal subjects at a predetermined treadmill speed. Seventeen non-disabled volunteers walked on a treadmill at 1.25 ms(-1). Temporospatial and kinematic data were collected while various support levels were applied (Minimal, 10, 30, 50 and 70% BWS). Compared to 10% BWS, significant temporospatial and kinematic changes were induced by 50 and 70% BWS. Fewer differences were induced by 30% BWS compared to 10% BWS. We concluded that gait patterns of unimpaired subjects are significantly changed by 50 and 70% BWS.

Frontal plane dynamic stability and coordination in subjects with cerebellar degeneration.

Objective attempts to characterize postural control in subjects with cerebellar (Cb) pathology have focused primarily on sagittal plane responses to static standing, semi-dynamic standing, and platform perturbation. Repeated, dynamic, functional movement may provide a better opportunity to study the effects of ataxia on frontal plane postural stability. The purpose of this investigation was to quantify lateral stability using center of gravity (CG) and center of pressure (CP) movement analysis, and to examine motor responses necessary to complete a repetitive stepping task. Whole body kinematic and kinetic data were collected as patients with Cb degeneration and non-disabled volunteers repeatedly ascended forward and descended backward from a 7.6-cm step to the beat of a metronome. Cb subjects demonstrated significantly greater lateral CG instability, consistent with increased CG velocity and displacement variability in the frontal plane compared to non-disabled subjects. Significantly greater lateral CP displacement was found in subjects with Cb degeneration. Phase plot patterns from patients with Cb degeneration showed poor movement quality, indicated by abruptly changing CG phase plot patterns and abnormal CG acceleration and deceleration phases. Ataxic postural reactions were observed consistently during lateral weight shifting phases toward the stance limb. We hypothesized that lateral postural instability in Cb subjects stems from altered lower extremity intersegmental coordination and inadequate lateral CG velocity control. Frontal plane CG instability may necessitate a wide-based gait. Despite the varied neuroanatomic sites of degenerative Cb pathology, subjects with Cb pathology demonstrated similar CG movement patterns and altered motor strategies to avoid destabilization. Dynamic assessment provides important information regarding frontal plane instability not revealed by static assessment methods. These findings suggest that a dynamic, constrained stepping task effectively differentiates Cb and non-disabled volunteers, contributing to our knowledge of the effect of ataxic movement disturbances on frontal plane postural stability and lower limb coordination.

Control accuracy and response time in multiple-state myoelectric control of upper-limb prostheses. Initial results in nondisabled volunteers.

In myoelectrically operated prosthetic systems control performance decreases with an increasing number of possible movements. A test has been designed that allows quantification of two related qualities of performance. A predefined amount of training was given to 40 nondisabled volunteers without previous prosthetic experience. After training they attempted the test. The two parameters measured were the response time and the control accuracy corresponding to the different movements. It is concluded that even with a very limited amount of training fairly complex control systems can be operated with acceptable performance.