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PubMed1997

Minimum energy trajectories of the swing ankle when stepping over obstacles of different heights.

This study was performed to test the hypothesis that the motion of the lower extremities when stepping over obstacles is governed by the criterion of minimum mechanical energy. The trajectories of the swing ankle during level walking and when stepping over obstacles of 51, 102, 153, and 204 mm heights were predicted and measured for eight healthy young adults. The predictions were made with a planar, seven-link linkage model based on the criterion of minimum mechanical energy using the method of dynamic programming. When stepping over obstacles, the predicted trajectories of the swing ankle were just high enough for the swing toe to clear the obstacles. The clearances measured between the obstacle and toe were significantly larger than those predicted. When stepping over obstacles the levels of work required to generate the measured trajectories were significantly larger (p < or = 0.002) than those required to produce the predicted trajectories. The amount of work necessary to generate the measured or predicted trajectories increased linearly (significant at p < or = 0.022) with obstacle height and, except when predicting the trajectory for the lowest obstacle, was significantly greater than that required when walking on level ground (p < 0.02). Thus, conservation of energy was found to become a less dominant criterion for governing the motion of the body when crossing obstacles than when walking on level ground.

Acceleration↗
PubMed1993

Cancer screening and prevention in primary care. Obstacles for physicians.

BACKGROUND: Surveys have demonstrated that primary care physicians are aware of cancer screening and prevention guidelines. However, health primary care providers do not recommend these services for many patients. This introductory discussion describes a new area of clinical study: practice barriers. METHODS: Literature review and the author's synthesis are used to identify major types of obstacles impeding broad implementation of cancer screening and prevention. RESULTS: Practitioners and patients face three types of obstacles: provider-specific obstacles; patient-specific obstacles; and health care delivery system obstacles. Provider-specific obstacles include lack of time, distraction by other health issues, lack of expertise, lack of positive feedback, and disagreement with recommendations. Barriers that chiefly affect screening for the major cancer sites (breast, colon, and cervix) and obstacles affecting preventive counseling also are discussed. Several techniques to help providers overcome obstacles have proven successful in increasing preventive activities. CONCLUSIONS: Efforts to increase cancer screening and prevention must focus on helping providers identify and overcome barriers through acquisition of needed skills, refinement of office time management, implementation of effective reminder systems, and development of appropriate, innovative feedback and reward mechanisms.

Female↗
PubMed2003

Obstacle avoidance during human walking: H-reflex modulation during motor learning.

The goal of this study was to investigate changes of H-reflex amplitudes during a motor learning task. Subjects with reduced vision were instructed to step over an obstacle on a treadmill as low as possible, while the soleus H-reflex was elicited. Acoustic warning and feedback signals about performance were provided. Performance improvement was associated with a decrease of muscle activity, needed to step over the obstacle (rectus femoris, biceps femoris, tibialis anterior and gastrocnemius medialis muscles), and of foot clearance, while joint angle trajectories from knee and ankle became more stable. The experiment consisted of five runs, three with normal treadmill walking and two with randomly stepping over the obstacle (100 times). H-reflexes were elicited at early and late stance phase before stepping over the obstacle. H/M ratio, latency and duration were determined. The values of these measures were calculated for the onset and end of a run and their course over time was evaluated using a correlation coefficient. The largest adaptations with a significant increase of reflex amplitude occurred during the first obstacle run. This increase lasted only briefly and the reflex amplitudes decreased to their previous values. During the later obstacle run, no H-reflex modulation occurred. It is concluded that a motor learning task causes adaptational effects not only on performance, but also on H-reflex responses. The results indicate that most of the modulation of H-reflexes is probably due to supraspinal influences on reflex transmission. The observations made are probably less specific for this motor task (stepping over the obstacle), but rather associated with the increased attention required by the motor learning task during the first obstacle run.

Adult↗
PubMed2004

Obstacle avoidance during locomotion using haptic information in normally sighted humans.

The goal of the study was to examine the accuracy and precision of control of adaptive locomotion using haptic information in normally sighted humans before and after practice. Obstacle avoidance paradigm was used to study adaptive locomotion; individuals were required to approach and step over different sizes of obstacles placed in the travel path under three sensory conditions: full vision (FV); restricted lower visual field (RLVF) using blinders on custom glass frames; and no vision (NV) using haptic information only. In the NV condition, individuals were a given an appropriate-sized cane to guide their locomotion. Footfall patterns were recorded using the GAITRite system, and lead and trail limb trajectories were monitored using the OPTOTRAK system, which tracked infrared diodes placed on the toes and the cane. Approach step lengths were reduced for the haptic condition: this slowed the forward progression and allowed greater time for haptic exploration, which ranged from 2.5 to 4 s and consisted of horizontal cane movements (to detect the width and relative location of the obstacle) and vertical cane movements (to detect the height of the obstacle). Based on feed-forward and on-line sensory (under both vision and haptic conditions) information about location of the obstacle relative to the individual, variability of foot placement reduced as the individual came closer to the obstacle, as has been shown in the literature. The only difference was that the reduction in variability of foot placement under haptic condition occurred in the last step compared with earlier under vision. Considering that the obstacle is detected only when the cane comes in contact, as opposed to vision condition when it is visible earlier, this difference is understandable. Variability and magnitude of lead and trail limb elevation for the haptic condition was higher than the RLVF and FV conditions. In contrast, only the magnitude of lead and trail limb elevation was higher in the RLVF condition when compared with the FV condition. This suggests that it is the inability of the haptic sense to provide accurate information about obstacle characteristics compared with the visual system, and not simple caution that lead to higher limb elevation. In the haptic and RLVF condition when vision was unavailable for on-line monitoring of lead limb elevation, kinesthetic information from lead limb elevation was used to fine-tune trail limb elevation. Both the control of approach phase and limb elevation findings held up even after sufficient practice to learn haptic guidance of adaptive locomotion in the second experiment. These results provide a clear picture of the efficacy of the haptic sensory system to guide locomotion in a cluttered environment.

Adaptation, Psychological↗
PubMed1987

Lateral diffusion in an archipelago. The effect of mobile obstacles.

Lateral diffusion of mobile proteins and lipids (tracers) in a membrane is hindered by the presence of proteins (obstacles) in the membrane. If the obstacles are immobile, their effect may be described by percolation theory, which states that the long-range diffusion constant of the tracers goes to zero when the area fraction of obstacles is greater than the percolation threshold. If the obstacles are themselves mobile, the diffusion constant of the tracers depends on the area fraction of obstacles and the relative jump rate of tracers and obstacles. This paper presents Monte Carlo calculations of diffusion constants on square and triangular lattices as a function of the concentration of obstacles and the relative jump rate. The diffusion constant for particles of various sizes is also obtained. Calculated values of the concentration-dependent diffusion constant are compared with observed values for gramicidin and bacteriorhodopsin. The effect of the proteins as inert obstacles is significant, but other factors, such as protein-protein interactions and perturbation of lipid viscosity by proteins, are of comparable importance. Potential applications include the diffusion of proteins at high concentrations (such as rhodopsin in rod outer segments), the modulation of diffusion by release of membrane proteins from cytoskeletal attachment, and the diffusion of mobile redox carriers in mitochondria, chloroplasts, and endoplasmic reticulum.

Cell Membrane↗
PubMed2001

Motion of the whole body's center of mass when stepping over obstacles of different heights.

Tripping over obstacles and imbalance during gait were reported as two of the most common causes of falls in the elderly. Imbalance of the whole body during obstacle crossing may cause inappropriate movement of the lower extremities and result in foot-obstacle contact. Thus, this study was performed to investigate the effect of obstacle height on the motion of the whole body's center of mass (COM) and its interaction with the center of pressure (COP) of the stance foot while negotiating obstacles. Six healthy young adults were instructed to perform unobstructed level walking and to step over obstacles of heights corresponding to 2.5, 5, 10, and 15% of the subject's height, all at a comfortable self-selected speed while walking barefoot. A 13-link biomechanical model of the human body was used to compute the kinematics of the whole body's COM. Stepping over the higher obstacles resulted in significantly greater ranges of motion of the COM in the anterior-posterior and vertical directions, a greater velocity of the COM in the vertical direction, and a greater anterior-posterior distance between the COM and COP. In contrast, the motion of the COM in the medial-lateral direction was less likely to be affected when negotiating obstacles of different heights.

Accidental Falls↗
PubMed2003

Saccade-stepping interactions revise the motor plan for obstacle avoidance.

The authors used a stimulus-response compatibility paradigm to assess the effect of changing the estimated time to obstacle contact. A limb-selection cue was presented in different phases of gait to young (n = 5) and to older (n = 4) adults while they were moving toward a foam obstacle in the walking path. A downward saccade was initiated after the cue; the saccade typically occurred during the stance phase of the target limb (the foot cued to lead the step over the obstacle). The mean saccade-step latency after the cue was on the order of -500 ms in both young and elderly participants. On reaching the obstacle, both groups generated an upward saccade approximately -300 ms before target footlift in both groups. Saccades following the limb-selection cue appeared to direct the gaze toward footfall targets just beyond the obstacle, whereas saccades generated just before obstacle footlift moved the gaze to the forward-looking direction. The elderly had significantly longer saccade-trailing-footlift latencies and prolonged gaze-fixation times than did the younger adults. Transient disruptions in optical flow appeared to be necessary for successful obstacle-avoidance behavior when there was an unexpected change in the estimated time to obstacle contact.

Adult↗
PubMed1996

Obstacle avoidance during locomotion is unaffected in a patient with visual form agnosia.

A patient (D.F.) who developed visual form agnosia following carbon monoxide-induced anoxia was assessed on three tests designed to measure her sensitivity to obstacle height in a locomotor task. Although her verbal estimates of the height of the obstacles were correlated with their actual height, the slope of the line relating estimated and actual obstacle height was much shallower than for control subjects. Similarly, when asked to estimate the height of the obstacle by raising one leg while standing nearby, the slope of line relating toe elevation and obstacle height was shallower than in control subjects. In contrast, D.F. was able to negotiate the same obstacles during locomotion as well as control subjects: toe elevation increased linearly as a function of obstacle height with similar slopes and correlation for the line relating toe elevation and obstacle height. These results provide additional support for the proposal by Goodale and Milner that the cortical pathways mediating the required transformations for the visual control of skilled actions are separate from those mediating experiential perception of the visual world.

Adult↗
PubMed2002

Foot strike patterns after obstacle clearance during running.

PURPOSE: Running over obstacles of sufficient height requires heel strike (HS) runners to make a transition in landing strategy to a forefoot (FF) strike, resulting in similar ground reaction force patterns to those observed while landing from a jump. Identification of the biomechanical variables that distinguish between the landing strategies may offer some insight into the reasons that the transition occurs. The purpose of this study was to investigate the difference in foot strike patterns and kinetic parameters of heel strike runners between level running and running over obstacles of various heights. METHODS: Ten heel strike subjects ran at their self-selected pace under seven different conditions: unperturbed running (no obstacle) and over obstacles of six different heights (10%, 12.5%, 15%, 17.5%, 20%, and 22.5% of their standing height). The obstacle was placed directly before a Kistler force platform. Repeated measures ANOVAs were performed on the subject means of selected kinetic parameters. RESULTS: The statistical analysis revealed significant differences (P < 0.004) for all of the parameters analyzed. The evaluation of the center of pressure and the ground reaction forces indicated that the foot strike patterns were affected by the increased obstacle height. Between the 12.5% and 15% obstacle conditions, the group response changed from a heel strike to a forefoot strike pattern. CONCLUSIONS: At height > 15%, the pattern was more closely related to the foot strike patterns found in jumping activities. This strategy change may represent a gait transition effected as a mechanism to protect against increased impact forces. Greater involvement of the ankle and the calf muscles could have assisted in attenuating the increased impact forces while maintaining speed after clearing the obstacle.

Adult↗
PubMed2000

Stepping performance during obstacle clearance in women: age differences and the association with lower extremity strength in older women.

OBJECTIVE: To compare stepping performance during obstacle clearance in younger and older women, and to examine the relationship between lower extremity strength and stepping performance during obstacle clearance in older women. DESIGN: Correlational study. SETTING: A small community. PARTICIPANTS: Twenty-four older women (mean age = 74.4), and 16 younger women (mean age = 20.7). The older participants lived independently in the community and were able to walk unaided. MEASUREMENTS: Lower extremity muscle strength, measures of stepping performance including reaction time, movement time, extent of obstacle clearance, time to clear obstacle, among others. MAIN RESULTS: The older women were far slower in stepping than the younger women. Toe trajectories differed between older and younger women during the initial portion of the step. The younger women tended to lift the toe straight up, whereas the older women tended to move the toe backward, away from the obstacle, passing farther from the obstacle when the toe cleared the obstacle height. There was little, if any, association between relative lower extremity strength and stepping performance during obstacle clearance in older women. CONCLUSIONS: Dramatic differences in the speed of volitional stepping performance were found between younger and older women. Among the older women, lower extremity strength was not related to volitional stepping performance.

Adult↗
PubMedDate not supplied

Modifying a functional obstacle course to test balance and mobility in the community.

A previously reported functional obstacle course (FOC) developed to assess elderly persons with and without balance and mobility impairment was used in a hospital-based study of 237 participants. A new modified version of the FOC was developed for use in a community-based study, by placing some obstacles next to walls instead of between parallel bars. These modifications eliminate the need for parallel bars or for extra personnel to interchange the obstacles. We were concerned that the modifications could affect performance scores, because touching or holding onto the now eliminated parallel bars could influence FOC scores under the original scoring system. To determine the effect of these modifications on FOC performance, we tested 36 volunteers, (18 fallers [falls within last year] and 18 non-fallers), on the modified parts of the old and new versions of the FOC. Random testing order and inter-trial rests were used. For both the old and new FOC versions, we summed quality and task completion time scores from the six modified obstacles (artificial turf, carpet, pine bark, sand, up ramp and down ramp) to create scores for quality and time. Our hypothesis was that there would be no performance difference between the original and modified obstacle course. Using a two-factor repeated-measures analysis of variance, we found no difference in quality scores between the two FOC versions and no effect of an interaction between faller status and the course versions. We did find that the time was approximately 2 seconds longer for the new version; however, the time increase was the same for fallers and non-fallers. These data show that fallers and non-fallers have comparable performance on both versions of the FOC; however, to compare the two obstacle courses we recommend an adjustment of 2 seconds in time scores. The obstacle course modifications will facilitate more extensive and efficient use of the obstacle course as a research tool to assess balance and mobility.

Accidental Falls↗
PubMed2002

The effect of obstacle conductivity and electric field on effective mobility and dispersion in electrophoretic transport: a volume averaging approach.

The method of volume averaging has been used to determine the effective electrophoretic mobility and dispersion coefficients for molecular transport of point-like solutes in a two-phase porous medium where the electrical conductivity and the diffusion and mobility coefficients may vary in both phases. The formal theory, derived in previous work, is numerically evaluated for cases where the obstacle phase has a large or small conductivity relative to the fluid phase and where the diffusion coefficient of the solute in the obstacle phase can be large or small relative to that in the fluid phase. In agreement with previous Monte Carlo methods, the effective electrophoretic mobility is not a function of media conductivity or electric field when the obstacles are impermeable to solute transport or have small diffusion solute diffusion coefficients. However, the dispersion coefficient is a strong function of electric field and varies with obstacle conductivity when diffusive transport is small in the obstacles relative to the fluid. In contrast, the effective electrophoretic mobility is a function of electric field when conductivity of the obstacles is much larger than the fluid and when the obstacles are very permeable to solute but have low electrical conductivity.

Electric Conductivity↗
PubMedDate not supplied

The reliability and validity of an obstacle course as a measure of gait and balance in older adults.

The use of an obstacle course to quantify gait, balance and functional mobility in elderly persons, particularly to assess objectively changes following exercise and rehabilitation interventions, has not been extensively developed or tested. In this study, we describe an 18-item obstacle course developed as an outcome measure for an exercise intervention among fall-prone elderly men. Reliability and validity of the obstacle course was tested in a group of 58 community-living elderly men (mean age = 75 years). Each subject's performance was videotaped and timed. The videotapes were scored by a physical therapist and a physician. Inter-rater reliability between the raters was high (Kappa = 0.96, p < 0.0001). Both the obstacle course score and time correlated significantly with gait velocity, a 6-minute walk test, and a performance-oriented instrument of gait and balance. Obstacle course scores showed significant improvement among the most impaired subjects, but not among higher functioning subjects following a 3-month exercise intervention. These results suggest that an obstacle course may be a useful and valid method for measuring outcomes related to mobility tasks in selected elderly populations. Further work is needed to determine in which populations, and for which outcomes, an obstacle course is better than simpler performance-based measures.

Aged↗
PubMed2000

Obstacle-induced transition from ventricular fibrillation to tachycardia in isolated swine right ventricles: insights into the transition dynamics and implications for the critical mass.

OBJECTIVES: The study was done to test the hypothesis that an artificial anatomical obstacle prevents the maintenance of ventricular fibrillation (VF) by stabilizing reentrant wavefronts (RWF) and increases the critical mass (CM) of myocardium required to sustain VF. BACKGROUND: Artificial obstacles can anchor RWF in simulated models of VF. Whether an artificial obstacle affects multiple-wavelet VF in real tissue is unclear. METHODS: The endocardial surfaces of seven isolated, perfused swine right ventricles were mapped using a plaque of 477 bipolar electrodes with 1.6-mm resolution. An 8-mm hole was punched in the tissue. The CM was reached by tissue mass reductions, at which VF converted to periodic activity (ventricular tachycardia, VT). RESULTS: After the creation of the obstacle, the VF cycle length increased from 71.6+/-18.4 ms to 87.5+/-13.0 ms (p<0.05). The obstacle, together with the papillary muscle, facilitated the transition from VF to VT by serving as attachment sites for the RWF. When one RWF attaches to the obstacle and another attaches to the papillary muscle, it may result in stable VT with figure-eight patterns. The CM for VF in the presence of an 8-mm hole (28.7+/-3.8 g) was higher than in the control group (swine right ventricles without holes, 24.0+/-3.4 g, p<0.05). CONCLUSIONS: An artificial anatomical obstacle induces slowing and regularization of VF, impairs the persistence of VF as judged by an increase of the CM, and can convert VF to VT by serving as an attachment site to reentrant excitation.

Animals↗
PubMed1996

Locomotor Patterns of the Leading and the Trailing Limbs as Solid and Fragile Obstacles Are Stepped Over: Some Insights Into the Role of Vision During Locomotion.

The issues explored in this article are the role of exproprioceptive input and the nature of exteroceptive input provided by the visual system in the control of limb elevation as obstacles are stepped over during locomotion. In the first experiment, the differences in limb trajectory of movements over solid and fragile obstacles of similar dimensions were examined. Subjects increased their toe clearance, vertical position of the hip, and the hip vertical velocity when going over a fragile obstacle with the leading limb. This suggests that in addition to visually observable properties of obstacles such as height or width, other properties, such as rigidity or fragility, which may be classified as visually inferred, also influence the limb trajectory. Part of the first and the second experiment was focused on understanding differences in leading limb and trailing limb trajectory over obstacles. The toe clearance of the trailing limb was lower for smaller obstacles. There was no consistent correlation between the toe clearance values of the leading and trailing limbs. The variability in toe clearance was higher for the trailing limb, which is attributable to lack of visual exproprioceptive input about trailing limb movements and to the shorter time available following toe-off to fine-tune the trailing limb trajectory. Because the body center of mass is moving toward the supporting foot when the trailing limb goes over obstacles and the trailing limb foot is moving up, the chances of a trip are minimized and recovery from an unexpected trip are more likely. These results highlight the role of exproprioceptive input provided by the visual system and possible cognitive influences on the limb trajectory as one travels over uneven terrains.

Journal Article↗
PubMedDate not supplied

Use of an obstacle course to assess balance and mobility in the elderly. A validation study.

An obstacle course, consisting of a series of 12 simulated functional tasks, has been developed to aid in the evaluation of rehabilitation interventions for elderly individuals with balance and mobility dysfunction. The validity of the obstacle course as a measure of balance and functional mobility was tested by comparing obstacle course performance scores of a sample of 237 community-dwelling veterans, aged 67 to 93 yr, with clinical indicators of balance and mobility including age, history of falls, symptoms of balance dysfunction, medication use, orthostatic blood pressure changes, neurologic examination abnormalities, muscle strength, joint range of motion, self-reported activity level, and functional status. Significant correlations were found between obstacle course scores and all clinical indicators except blood pressure changes and age. Multiple regression analysis of selected variables showed that activity level and neurologic abnormalities best determined both qualitative and quantitative obstacle course performance. Non-fallers performed significantly better on the obstacle course than fallers. These results suggest that the obstacle course is valid and has potential as a useful tool in the evaluation of older persons with balance and mobility impairment.

Aged↗
PubMed1993

Obstacles to and motivation for successful breast-feeding.

This study determined obstetric physiotherapists' perceptions about major obstacles to and methods of motivation for successful breast-feeding by means of the Friedman non-parametric procedure for the two-way analysis of variance. Three categories of obstacles were identified: maternal obstacles, health professionals and society. Maternal obstacles mentioned most were insufficient motivation (25%) and knowledge (24%), anxiety (14%), fatigue (14%), and employment (14%). Obstacles related to health professionals included lack of support for mothers (20%), inappropriate lactation management (19%), lack of knowledge (15%), negative attitudes (5%), and staff shortages (5%). With regard to society, lack of support (27%) and life-styles (29%) were identified as significant obstacles. The two most significantly important methods of motivation were information and education (53%) and contact with other breast-feeders (27%). It is concluded that breast-feeding education efforts can be improved by identifying obstacles to breast-feeding and methods of motivation and that the Friedman test may be a statistical procedure to consider for determining priorities.

Adult↗
PubMed1995

Computer simulation of the directional displacement of rod-shaped, arc-shaped, and circular objects in an array of obstacles, representing a simple model for the gel electrophoresis of small DNA.

The gel electrophoresis of DNA of identical length but various static conformations was simulated using a two-dimensional model of the movement of rod-shaped, arc-shaped, and circular objects through random arrays of disk-shaped obstacles. At low obstacle density, the displacement rate of these objects decreases from the rod-shaped to the circular to the arc-shaped objects. At high obstacle densities, the displacement rate of circular objects approaches zero. The alignment of the arc-shaped objects along the axis of the directional movement of the objects were retarded in their movement by collisions with the obstacles; the number of collisions of the former, in view of their greater ability to align, was less than that of the latter. Circular objects were exclusively retarded by collisions, while the arc-shaped objects exhibited an additional retarding mechanism, viz. the suspension ("hanging") on the obstacles. When the rigid objects were made flexible, their displacement increased. The increase was most pronounced with the circular objects, allowing them to penetrate at obstacle densities from which the rigid objects were excluded.

Computer Simulation↗