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PubMed2004

Characteristics of stepping over an obstacle in community dwelling older adults under dual-task conditions.

Previous research suggests that older adults may have difficulty attending to simultaneous tasks. This study was conducted to determine how concurrent performance of a secondary cognitive task influences walking and stepping over an obstacle in community dwelling older adults. Twenty-one men and women with a mean age of 73.4 years (S.D.=5.3) participated in the study. Subjects performed a gait task both alone (single-task condition) and in combination with a cognitive task that involved reciting numbers (dual-task condition). In the gait task, each subject walked at his/her fastest speed along a 10-m walkway and stepped over an obstacle designed to simulate a door threshold. Paired t-tests were used to compare gait parameters (10 m gait speed, gait speed during obstacle approach and negotiation, medial-lateral center of pressure excursion and velocity during obstacle negotiation, foot clearance over the obstacle, step length and foot position relative to the obstacle) and cognitive task performance under single and dual-task conditions. Toe-obstacle distance was greater and obstacle-heel distance was reduced under dual-task conditions. Performance of the remaining gait parameters did not change with the addition of a secondary cognitive task. Cognitive task performance decreased under dual-task conditions. These community dwelling older adults demonstrated minimal or no change in measured gait parameters during simultaneous performance of a cognitive task. The observed decrement in cognitive task performance suggests that subjects may have placed a higher priority on gait performance.

Aged↗
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↗
PubMed2005

Age-dependent differences in the attentional demands of obstacle negotiation.

BACKGROUND: Although the attention directed to gait does increase as an impending obstacle nears, it remains unclear whether the allocation of attentional resources differs between the precrossing phase of obstacle negotiation and the crossing phase of this task. This study compared the attentional demands associated with steady-state walking and the precrossing and crossing phases of an obstacle-negotiation task between young and older adults. METHODS: Fifteen younger and 15 older adults participated in this study. Participants were required to perform a verbal reaction time task during three events: (1) steady-state unobstructed gait, (2) precrossing (the final full stride prior to obstacle crossing), and (3) obstacle crossing. RESULTS: The attention directed during precrossing exceeds that of steady-state walking for both younger and older adults. Younger adults direct more attention to gait during precrossing than they do during crossing. However, precrossing is equally attentionally demanding as crossing for older adults, and both of these events require more attention than does steady-state gait in this age group. CONCLUSIONS: The task of obstacle negotiation, from precrossing through obstacle crossing, is attentionally demanding for elderly persons, and fall risk, due to a compromised availability of attentional resources, does occur prior to obstacle crossing in this age group.

Accidental Falls↗
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↗
PubMed2006

Long-lasting memories of obstacles guide leg movements in the walking cat.

We examined the ways in which memories of previously seen obstacles can alter the stepping of walking cats. Cats were paused after the forelegs, but not the hindlegs, had stepped over an obstacle. Near the beginning of a variable delay period, the obstacle was lowered. On the subsequent step, the path of the hindlegs allowed us to make inferences about whether the memory of the obstacle was influencing leg movements. We present two main findings. First, the memory of the obstacle persisted for the duration that the animal straddled the original location of the obstacle. In one instance, this interval was 10 min. Second, this memory includes information regarding the size and position of the obstacle relative to the animal. This information is used to plan foot placement and to redirect the step in mid-swing to avoid the previous position of the obstacle.

Animals↗
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↗
PubMed2005

Stepping over obstacles of different heights: kinematic and kinetic strategies of leading limb in hemiplegic children.

Twelve hemiplegic children (HC) and five normally developing children (NDC) were instructed to walk barefoot over a level surface and to cross obstacles of various heights (0%, 10%, 15% and 20% of their leg lengths). Kinematic and kinetic strategies of their leading limb were mainly examined. For the starting position of the trials HC was adjusted so that the affected limb was the leading one, while NDC step over the obstacle with their preferred selection of leading and trailing limb. The results demonstrated that the crossing speed was decreased and the crossing swing phase was increased in both groups. The toe vertical clearance augmented with the presence of the obstacle, but it remained constant with obstacle heights. The toe and heel horizontal distances of the leading limb remained constant with all obstacle heights. The toe horizontal distances of the trailing limb in HC increased with obstacle heights outlying a peculiar strategy. A comparison of joint angles and power variations revealed substantial differences in height changes between the two groups: HC exhibited a preferential modulation of pelvis and hip joints and a reduced modulation of knee and ankle joints. The knee flexor limitation in HC was accomplished by knee power variations near the toe-off. HC showed also an increased ankle involvement of the support limb, i.e. the almost normal limb. Collectively, the results provided insights into multijoint variations of locomotor act caused by visible obstacle in HC and indicate that a correct rehabilitation treatment should be focused on the use of dynamic constraints preferentially at the plegic knee.

Analysis of Variance↗
PubMed2006

Pain relief in knee osteoarthritis reduces the propensity to trip on an obstacle.

The pain associated with knee osteoarthritis (OA) has been shown to lead to an increased propensity to trip on an obstacle. Pain-relieving intra-articular injections are widely utilized in the treatment of knee OA. This study examined the effects of pain-relieving intra-articular knee injections on the ability to avoid contacting a suddenly appearing obstacle in patients with knee OA. Obstacle avoidance success rates, pain, body mass index, visual acuity, contrast sensitivity, depth perception, and single-leg stance duration were evaluated in nine patients with painful osteoarthritis of the knee and 14 age-matched healthy control subjects. Obstacle avoidance success rates, pain, and single leg stance duration were tested a second time in the patients with knee OA after they received their injections, which contained a fast-acting local anesthetic to provide rapid pain relief. After receiving the pain-relieving knee injections, patients with knee OA had 48% less pain and were 31% more successful in avoiding stepping on the obstacle. However, after receiving the injection, the obstacle avoidance success rates remained 20% less than those of the healthy controls. The results of this study suggest that knee pain-relief can decrease the propensity of people with painful knee OA to trip and fall over an obstacle. However, pain-relief alone did not return the patients with knee OA in this study to a disease-free risk of tripping.

Accidental Falls↗
PubMed2005

Advancing age progressively affects obstacle avoidance skills in the elderly.

The ability to adequately avoid obstacles while walking is an important skill that allows safe locomotion over uneven terrain. The high proportion of falls in the elderly that is associated to tripping over obstacles potentially illustrates an age-related deterioration of this locomotor skill. Some studies have compared young and old adults, but very little is known about the changes occurring within different age groups of elderly. In the present study, obstacle avoidance performance was studied in 25 young (20-37 years) and 99 older adults (65-88 years). The participants walked on a treadmill at a speed of 3 km/h. An obstacle was dropped 30 times in front of the left foot at various phases in the step cycle. Success rates (successful avoidance) were calculated and related to the time available between obstacle appearance and the estimated instant of foot contact with the obstacle (available response times or ARTs ranging from 200 to more than 350 ms). In addition, latencies of avoidance reactions, the choice of avoidance strategies (long or short step strategy, LSS or SSS), and three spatial parameters related to obstacle avoidance (toe distance, foot clearance, and heel distance) were determined for each participant. Compared to the young, the older adults had lower success rates, especially at short ARTs. Furthermore, they had longer reaction times, more LSS reactions, smaller toe and heel distances, and larger foot clearances. Within the group of elderly, only the 65-69 year olds were not different from young adults with respect to success rate, despite marked changes in the other parameters measured. In particular, even this younger group of elderly showed a dramatic reduction in the amount of SSS trials compared to young adults. Overall, age was a significant predictor of success rates, reaction times, and toe distances. These parameters deteriorated with advancing age. Finally, avoidance success rates at short ARTs were considerably worse in elderly participants who sustained recurrent falls in the six-month period prior to the assessment compared to those who sustained no or only one fall. An exercise program has been shown to improve avoidance success rates, especially at short ARTs, but the training effects on the determinants of success still need to be assessed.

Accidental Falls↗
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↗
PubMed2005

Osteoarthritis of the knees increases the propensity to trip on an obstacle.

Tripping on an object is the most frequent cause of falls. We examined the effects of painful osteoarthritis of the knee on obstacle avoidance success rates in older adults. Obstacle avoidance success rates, pain, body mass index, visual acuity, contrast sensitivity, depth perception, and single-leg stance duration were evaluated in 17 patients with painful osteoarthritis of the knees (age range, 59.6 +/- 8.1 years) and 14 age-matched healthy control subjects (age range, 61.1 +/- 10.0 years). The patients with osteoarthritis of the knees had a 37% lower obstacle avoidance success rate, a 54% lower single-leg stance duration, and a 24% greater body mass index than the control subjects. Age, visual acuity, contrast sensitivity, and depth perception were not different between the two groups. Obstacle avoidance success rates and single-leg stance durations decreased linearly as pain increased in the patients with osteoarthritis of the knees. Obstacle avoidance success rates also decreased linearly as single-leg stance duration decreased in the patients with osteoarthritis of the knees. Osteoarthritis of the knees reduced obstacle avoidance success rates, supporting epidemiologic studies that have found osteoarthritis to be a risk factor for falls. This study showed that pain associated with osteoarthritis of the knees increased the propensity to trip on an obstacle (the greater the pain the greater the propensity to trip and fall) and underscores the importance of treating pain associated with osteoarthritis.

Accidental Falls↗
PubMed2004

Footlift asymmetry during obstacle avoidance in high-risk elderly.

OBJECTIVES: To test the hypothesis that vertical footlift asymmetries and low obstacle clearing distance during obstacle avoidance are characteristics of elderly people classified as high risk for falls. DESIGN: Controlled cross-sectional design with two conditions to cue selection of the foot-for-step initiation: sound cue and visual cue. SETTING: Senior independent living facilities. PARTICIPANTS: Eighteen community-dwelling elderly with a history of falling or prolonged Timed Up and Go score greater than 13.5 seconds, 16 elderly with no fall history and Timed Up & Go score of 13.5 seconds or less, and 15 younger subjects. MEASUREMENTS: Video kinematic analysis of bilateral footlift displacement and velocity using reflective markers as subjects stepped over foam obstacles scaled to a maximum tolerated height. RESULTS: High-risk elders contacted the obstacle more frequently and had significantly greater vertical footlift asymmetries adjusted for obstacle/subject height (mean+/-standard error asymmetry index for sound cue 3.25+/-0.42 cm, for visual cue 2.51+/-0.45 cm) than low-risk and younger subjects (P<.001). In low-risk elderly and younger subjects, the asymmetry index approached 0, which indicated symmetrical lower limb movements when stepping over the obstacles. CONCLUSION: High-risk elderly show a marked asymmetry in foot clearance while stepping over an obstacle, with the lag foot clearing the obstacle at a much lower distance than the lead foot. Possible mechanisms responsible for these findings (limited hip extension and deficits in executive cognitive function) are discussed.

Accidental Falls↗