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PubMed1997

Obstacle avoidance and a perturbation sensitivity model for motor planning.

A novel obstacle avoidance paradigm was used to investigate the planning of human reaching movements. We explored whether the CNS plans arm movements based entirely on the visual space kinematics of the movements, or whether the planning process incorporates specific details of the biomechanical plant to optimize the trajectory plan. Participants reached around an obstacle, the tip of which remained fixed in space throughout the experiment. When the obstacle and the start and target locations were rotated about the tip of the obstacle, the visually specified task constraints retained a rotational symmetry. If movements are planned in visual space, as indicated from a variety of studies on planar point-to-point movements, the resulting trajectories should also be rotationally symmetric across trials. However, systematic variations in movement path were observed as the orientation of the obstacle was changed. These path asymmetries can be accounted for by a class of models in which the planner reduces the likelihood of collision with the obstacle by taking into account the anisotropic sensitivity of the arm to external perturbations or uncertainty in joint level control or proprioception. The model that best matches the experimental results uses planning criteria based on the inertial properties of the arm.

Arm↗
PubMed2003

The influence of obstacles on the speed of grasping.

The movement time of a reach-to-grasp movement increases when obstacles are placed close to the target object. We investigated whether this increase can best be explained by limits on the grip aperture or by limits on the paths of the individual digits. In our experiment subjects were instructed to pick up an object with their index finger and thumb. There was an obstacle at either side of the object. The increase in movement time when either obstacle was placed closer to the object was best described by a model in which the movement amplitude and the distance between each obstacle and the target object are independent factors. We conclude that the way that obstacles influence the movement time in reach-to-grasp movements is determined by the extent to which they limit the digits' paths.

Efficiency↗
PubMed2003

Locomotor adjustments for circumvention of an obstacle in the travel path.

Independent living requires the navigation of a surrounding environment which is often cluttered with obstacles. When walking around an obstacle in the travel path, safe clearance requires some degree of body-segment reorientation. While body-segmental coordination strategies have been well studied for steering tasks that require moving the body in a new walking direction, it has never been established just what coordination strategies are used in different walking tasks. To address this issue, the current study was designed to investigate the timing of body segment coordination strategies and whole-body anticipatory locomotor adjustments employed when circumventing an obstacle placed in the travel path. Six healthy adults were asked to walk at their natural pace during unobstructed walking, as well as during avoidance to the right or left of a cylindrical obstacle (OBS) located in the travel path. Data analyzed were center of mass (COM) clearance from the OBS, forward velocity, step length and width, yaw angles of the head and trunk, roll angle of the trunk, and medial-lateral COM displacement. Onset of change in these variables from unobstructed walking was calculated as the time from OBS crossing. Avoidance involved two equally used strategies: lead limb close to or away from the OBS during the crossing step. Medial-lateral COM deviations were controlled by changes in step width without changes in trunk roll. There were no differences in the onset times of body segment reorientation for path deviation. These results are in contrast to previous studies on change in travel direction where the head segment initiates the body reorientation. Contrary to a steering task, circumventing an obstacle requires a different coordination for a transient change in COM trajectory with the underlying travel-direction maintained.

Adult↗
PubMed2005

Determinants guiding alternate foot placement selection and the behavioral responses are similar when avoiding a real or a virtual obstacle.

In this study we validate the use of a virtual planar obstacle paradigm to study the avoidance of a real obstacle, such as a hole, during locomotion. Also we further validate the economy determinant implicated with the minimization of foot displacement from its normal landing position during alternate foot placement. Participants were asked to perform two blocks of trials: real (a real hole was embedded in the pathway and participants were requested to avoid stepping into it) and virtual (a virtual planar obstacle was displayed on the screen of a liquid crystal display monitor). Trunk and feet kinematics were monitored, as well as electromyography (EMG) activity of 14 muscles of both lower limbs and trunk. The results of this study showed that the dominant choice for each obstacle investigated was not different between the real and virtual conditions. In addition, dynamic stability, economy and forward progression determinants guiding alternate foot placement were similarly satisfied. Thus the use of virtual planar obstacle in adaptive locomotion study is appropriate. EMG data were used to compute an index relating the changes in muscle activity relative to the normal walking profile. This EMG index was significantly and positively correlated with the amount of foot displacement for the adaptive step. The fact that the dominant choice resulted in minimum foot displacement from its normal landing spot combined with minimal changes in muscle activity validates conclusively the economy determinant.

Adolescent↗
PubMed1994

Situational obstacles to dietary adherence for adults with diabetes.

OBJECTIVE: To develop a taxonomy of everyday situations that create obstacles for adherence to dietary management in patients with diabetes. SUBJECTS: Twenty-six adults with diabetes (12 with insulin-dependent diabetes mellitus and 14 with non-insulin-dependent diabetes mellitus) were recruited from an outpatient diabetes clinic. MAIN OUTCOME MEASURES: Subjects were interviewed to identify problem situations that create obstacles for dietary adherence. The resulting 69 situations were judged for the presence or absence of 32 environmental features using a reliable coding system. STATISTICAL ANALYSIS: A hierarchical cluster analysis was used to identify homogeneous groups of dietary adherence obstacles. RESULTS: Twelve types of problem situations were identified: negative emotions, resisting temptation, eating out, feeling deprived, time pressure, tempted to relapse, planning, competing priorities, social events, family support, food refusal, and friends' support. CONCLUSIONS: The resulting taxonomy provides an outline for the detailed assessment of obstacles to dietary adherence. An individual's ability to cope with this array of obstacles to dietary adherence should be assessed so treatment can be individualized.

Adult↗
PubMed2005

Comparisons of the lower limb kinematics between young and older adults when crossing obstacles of different heights.

Fifteen young and 15 older healthy adults walked and crossed obstacles with heights of 10%, 20% and 30% of their leg lengths while their kinematic data were measured with a three-dimensional (3D) motion analysis system. End-point variables together with 3D joint kinematics of both the leading and trailing limbs were obtained. The results showed that the older group adopted a swing hip flexion strategy to achieve a higher leading toe clearance than the young group. With increasing obstacle height, the older group increased linearly the leading toe clearance by changing fewer joint angular components than the young group, allowing the maintenance of the necessary stability of the body with minimum control effort. When the trailing limb was crossing, the older group showed no significant difference in the trailing toe clearance compared to the young group, although different joint kinematic patterns were evident. The older group seemed to use a more conservative strategy for obstacle-crossing. Failure to implement this strategy during obstacle negotiation may increase the risk of falls owing to an inability to recover from unexpected tripping or stumbling. The results of this study suggest that existing knowledge of the kinematic control of obstacle-crossing based on young subjects may serve as a baseline for further studies on older people for a better understanding of the mechanisms and for the prevention of falls in the elderly.

Accidental Falls↗
PubMed2004

Gait adjustments in response to an obstacle are faster than voluntary reactions.

It has been reported that obstacle avoidance reactions during gait have very short latencies. This raises the question whether the cortex can be involved, as it is in voluntary reactions. In this study, latencies of obstacle avoidance (OA) reactions were determined and related to latencies of voluntary stride modifications and simple reaction times (SRT) of hand and foot. Twenty-five healthy young adults participated in this study. While they were walking on the treadmill, an obstacle suddenly fell in front of their left leg. The first reaction to the obstacle was the moment at which the differentiated acceleration curve of the foot deviated from the control signal. Latencies of OA reactions were 122 ms (SD 14 ms) on average. Two very different avoidance reactions (lengthening and shortening of the stride) were noticed, but there was no avoidance strategy effect on OA latencies. OA latencies were significantly shorter as compared to latencies of voluntary stride modifications and simple reaction times of hand and foot. The short OA latencies could not only be explained from the dynamic nature of the task. It is suggested that subcortical pathways might be involved in obstacle avoidance.

Cues↗
PubMed2004

The effects of walking speed on obstacle crossing in healthy young and healthy older adults.

The effects of walking speed and age on the peak external moments generated about the joints of the trailing limb during stance just prior to stepping over an obstacle and on the kinematics of the trailing limb when crossing the obstacle were investigated in 10 healthy young adults (YA) and 10 healthy older adults (OA). The peak hip and knee adduction moments in OA were 21-43% greater than those in YA (p<or= 0.046). The angular velocity of hip flexion from toe-off to when the toe was over the obstacle in OA was 20% less than that in YA (p=0.048). Eight external peak moments about the hip, knee, or ankle increased significantly with speed in both groups (p<or=0.01); the largest in the sagittal plane was 62% for knee flexion (p<or=0.0001). Toe-obstacle clearance was not affected. Trailing foot placement was affected by speed, but not by age. Speed produced a small change ( approximately 1 degrees ) in knee abduction-adduction, the only joint angle affected (p=0.022). The greater magnitudes of hip and ankle adduction moments occurring in the trailing limb of OA place larger demands on the hip and ankle abductors of the trailing limb to maintain dynamic balance when stepping over the obstacle with the leading limb.

Adult↗
PubMed2006

Emergency nurses' perceptions of obstacles and supportive behaviors in end-of-life care.

INTRODUCTION: Little is known about emergency nurses' perceptions of either obstacles or supportive behaviors for providing end-of life (EOL) care to dying patients. The purpose of this study was to determine the perceived obstacles and supportive behaviors in providing EOL care to dying patients in emergency departments. METHODS: In this survey research, a 73-item questionnaire regarding EOL care was mailed to a geographically dispersed national random sample of 300 members of the Emergency Nurses Association. Descriptive statistics were calculated for the 54 Likert-type items and demographic items. Two open-ended questions were analyzed using content analysis. RESULTS: Returns after 3 mailings yielded 169 usable questionnaires from 284 eligible respondents for a return rate of 59.5%. The greatest obstacles were: (1) emergency nurses having too great a work load to care for dying patients; (2) emergency nurses having to deal with angry family members; and (3) the poor design of emergency departments that do not allow for privacy of dying patients or grieving family members. The most supportive behaviors were: (1) good communication between the physician and RN caring for the dying patient; (2) physicians meeting in person with the family after the patient's death; and (3) an emergency department designed so that the family has a place to grieve in private. DISCUSSION: Having a better understanding of emergency nurses' perceptions of obstacles and supportive behaviors in providing end-of-life care could help decrease the stress of caring for dying patients. Actions could be taken to decrease the highest rated obstacles and increase the ratings of supportive behaviors that may ultimately result in better end-of-life care for dying patients and their families in the emergency setting.

Communication↗
PubMed2006

Any way you look at it, successful obstacle negotiation needs visually guided on-line foot placement regulation during the approach phase.

In the two experiments discussed in this paper we quantified obstacle avoidance performance characteristics carried out open loop (without vision) but with different initial visual sampling conditions and compared it to the full vision condition. The initial visual sampling conditions included: static vision (SV), vision during forward walking for three steps and stopping (FW), vision during forward walking for three steps and not stopping (FW-NS), and vision during backward walking for three steps and stopping (BW). In experiment 1, we compared performance during SV, FW and BW with full vision condition, while in the second experiment we compared performance during FW and FW-NS conditions. The questions we wanted to address are: Is ecologically valid dynamic visual sampling of the environment superior to static visual sampling for open loop obstacle avoidance task? What are the reasons for failure in performing open loop obstacle avoidance task? The results showed that irrespective of the initial visual sampling condition when open loop control is initiated from a standing posture, the success rate was only approximately 50%. The main reason for the high failure rates was not inappropriate limb elevation, but incorrect foot placement before the obstacle. The second experiment showed that it is not the nature of visual sampling per se that influences success rate, but the fact that the open loop obstacle avoidance task is initiated from a standing posture. The results of these two experiments clearly demonstrate the importance of on-line visual information for adaptive human locomotion.

Adolescent↗
PubMed2003

The effects of improved strength on obstacle negotiation in community-living older adults.

Poor mobility has been associated with age-related deterioration in muscle strength. While previous work has examined the effects of improved strength on level walking, we have quantified the effects of a resistance-training program on obstructed gait tasks using biomechanical-dependent measures. Forty-five community-dwelling participants aged 62 years or older were randomised to either a control (n=16) or experimental group (n=29). The experimental subjects exercised for 24 weeks on a progressive resistance-training program designed to improve lower body strength. Dynamic strength was assessed at weeks 0 and 24 as well as specific laboratory gait kinetics and kinematics during stepping over an obstacle and negotiation of a raised surface set at 10, 20 and 30% of each subject's leg length. Significant strength improvements (P<0.05), ranging between 197 and 285%, were recorded in the experimental group. The strength gains in the experimental group were accompanied by significant increases in obstacle-crossing stride velocity (range 5.5-15.5%) due to increases in stride length and decreases in stride duration for both gait tasks. Significant changes in the peak vertical and anterior-posterior ground reaction forces as well as in kinematic variables associated with a safe obstacle traverse such as vertical obstacle heel clearance, limb flexion at obstacle crossing, horizontal foot placement and vertical landing velocity resulted in an improved crossing strategy in the experimental subjects. These findings provide evidence of significant improvements in obstructed gait function of community-living older adults associated with a systematic resistance-training program.

Age Factors↗
PubMed2004

Obstacle negotiation kinematics: age-dependent effects of postural threat.

This study investigated whether obstacle negotiation kinematics among younger (YA) and older adults (OA) are influenced by postural threat. Obstacle negotiation kinematics among YA and OA were examined under four conditions of postural threat. Seventeen older and 15 YA negotiated a fixed virtual obstacle while walking at a self-determined velocity along a 7.2 m walkway. Postural threat was manipulated by varying the width (0.60 vs. 0.15 m) and height (0.00 vs. 0.60 m) of the walkway. Increasing postural threat resulted in elevated levels of physiological arousal and altered crossing kinematics for all subjects. Specifically, crossing step length, lead limb velocity, trail limb velocity, and whole body center of mass (COM) velocity decreased and lead limb crossing height increased in the condition of greatest postural threat compared with the condition of least postural threat. Although both YA and OA altered obstacle negotiation kinematics under conditions of postural threat, the changes observed among older adults were considerably different from those of YA. In particular, OA demonstrated more marked reductions in the crossing velocity of the lead limb, trail limb, and COM than YA between the condition of least postural threat and the condition of greatest postural threat. The results of this study reveal that postural threat influences negotiation kinematics among YA and OA and illustrate that age-dependent differences exist for obstacle negotiation kinematics when postural threat increases. These findings may imply a beneficial effect of fear of falling on reducing fall probability among healthy OA.

Accidental Falls↗
PubMed1998

Learning a motor task involving obstacles by a multi-joint, redundant limb: two synergies within one movement.

In this study, we investigated the hypothesis that the problem of motor redundancy could be solved using synergies representing rules for relative joint involvement to ensure a desired endpoint trajectory which may be context-dependent and may change with practice. Subjects practised a planar movement 'as fast as possible' from an initial to a final position, avoiding three round obstacles. The improvement in motor performance included a decrease in movement time and in the error scores. It was accompanied by the emergence of two distinct synergies. The first one involved elbow and shoulder movements and was used to move from the initial position to the first obstacle, and from obstacle to obstacle, whereas the second, involving the wrist, was used while going around the obstacles. The first synergy was seen before practice and showed an increase in joint coupling with practice. The second synergy was not seen prior to practice; it could not be explained by the pseudo-inverse transformation. We concluded that the central nervous system (CNS) has options for solving the redundancy problem, and that the solutions may be chosen based on such considerations as accuracy requirements, inertial properties of segments, and efficacy of particular joints to move the endpoint along a desired trajectory.

Acceleration↗
PubMed2002

Heart failure in primary care: qualitative study of current management and perceived obstacles to evidence-based diagnosis and management by general practitioners.

BACKGROUND: Chronic heart failure is a common clinical condition with high morbidity and mortality. Despite the evidence that appropriate treatment with angiotensin-converting enzyme inhibitors can improve morbidity, primary care studies show that patients with heart failure are incorrectly diagnosed and inadequately treated. AIM: To explore general practitioners' accounts of their management of patients with heart failure and identify the perceived obstacles to diagnosis and management. METHODS: We conducted this qualitative study using semi-structured interviews in 18 general practices. The practices were stratified on the basis of size, location, and the level of practice development. The interviews were based on a schedule of open questions based on the literature on diagnosis and management of patients with heart failure. Transcriptions of the audiotaped interviews were independently analysed by two researchers and analysis was based on open coding using a constant comparative approach. Categories were reduced to major themes. RESULTS: General practitioners suspect heart failure when patients present with breathlessness or ankle oedema. Many general practitioners reported that they would diagnose heart failure after respiratory examination and a positive finding of basal crepitations. Many general practitioners arrange a chest X-ray to establish the diagnosis and some arrange an electrocardiogram. A few general practitioners mentioned that they diagnosed heart failure with a trial of diuretics. Obstacles to diagnosis were mentioned by most general practitioners and included lack of facilities for appropriate investigations (especially echocardiography) and lack of time and expertise. Obstacles to management included lack of time, high cost of drugs, difficulty with diagnosis, selection bias towards younger patients and not having the confidence to initiate angiotensin-converting enzyme inhibitors. Many general practitioners were unaware of the impact angiotensin-converting enzyme inhibitors can have on morbidity and mortality. CONCLUSIONS: Although symptoms of heart failure are not sufficiently specific for diagnosing patients with heart failure, many general practitioners in European countries treat people with suspected heart failure on the basis of symptoms and signs alone. This study has identified many obstacles to the diagnosis and management of heart failure that may explain why patients are inadequately managed in primary care. Specific implementation strategies need to be tailored to overcome these obstacles.

Aged↗
PubMed2005

Gait adaptation of children with cerebral palsy compared with control children when stepping over an obstacle.

This study investigated the adaptive gait pattern in obstacle clearance in 12 normally developing (ND) children (six males, six females; mean age 10y 2mo, SD 10mo) and 12 children who had spastic diplegic cerebral palsy (CP) and who were independent ambulators (10 males, two females; mean age 13y 5mo, SD 2y 7mo). Children in both groups had 8 to 12 years of walking experience. They walked up to and crossed over obstacles of a height of 0%, 10%, and 20% of their leg length. Kinematic aspects of the three-dimensional leg movements were captured with the Vicon system and analyzed with one-way analysis of variance with repeated measure. Both groups increased foot clearance for higher obstacles. Children with CP were slower in approach and crossing speed, and used a wider base of support than the ND children when the obstacle height was increased. Results suggest that motor problems in obstacle clearance in children with CP lie in the implicit process of motor control, i.e. torque dynamics, not the explicit process, i.e. movement-match with the environmental constraints.

Adolescent↗
PubMed2004

Integration of the recommendations of the Canadian Task Force on Preventive Health Care: obstacles perceived by a group of family physicians.

BACKGROUND: Surveys conducted in North America and in several European countries show that the preventive activities recommended by some groups of experts are difficult to integrate into medical practice. Interventions to correct this problem have produced mitigated results. OBJECTIVES: Our aim was to gain a better understanding of the obstacles perceived by a group of family physicians concerning the integration of prevention into their routine practices. METHODS: A qualitative design was selected to facilitate the exploration of that topic. Seven focus groups with 35 physicians practising in the Montreal area were conducted. Questions regarding their perception of, and obstacles to, the integration of prevention in their daily work were explored. The text of these interviews was analysed following the content analysis method. Codification of the important themes that were identified was done by two of the researchers. RESULTS: We met with 35 family physicians in two regions in Montreal, Quebec. The lack of motivation on the part of users and the lack of value placed on continuity of care appear to be the main obstacles in the eyes of the physicians, followed by a lack of financial incentives, work overload, and contradictions among the recommendations. In addition, other obstacles were observed by the researchers: limited intervention strategies on the part of physicians to support behaviour modification among patients, non-recognition of the importance of the organization of practice and inability to acknowledge the obstacles that can be ascribed to their own beliefs. CONCLUSION: The family physicians we met identified several barriers to the integration of prevention in their practices. The interventions proposed to date do not address the barriers perceived by the physicians in our study. Continuing medical education activities focus on knowledge, while the difficulties expressed relate more to communication skills coupled with a feeling of powerlessness. The physicians we met with do not seem to consider recall systems and looking at their organization of practice as possible solutions. The physicians seem to 'cave in' under the weight of the responsibilities that have been assigned to them in terms of health promotion. There may be room for proposing a more realistic menu. This study identifies a need for much more specific and concrete training on communication and counselling skills.

Adult↗
PubMed2006

Comparison of health care professionals' and surveyors' opinions on problems and obstacles in implementing quality management system in Thailand: A national survey.

OBJECTIVE: To explore problems and obstacles of hospitals in Thailand implementing quality management systems according to the hospital accreditation (HA) standards. DESIGN: Questionnaire survey. SETTING: Thirty-nine hospitals in all 13 regions of Thailand. PARTICIPANTS: A total of 728 health care professionals and 41 surveyors of the national accreditation program. MAIN OUTCOME MEASURES: Health care professionals' and surveyors' opinions on problems and obstacles in 24 items representing Thailand HA standards. RESULTS: The response rates were 94.9 and 73.2% in health care professionals and surveyors, respectively. More than 90% of both groups thought that there had been problems in the items such as 'quality improvement (QI) activities' and 'integration and utilization of information'. The items considered by health care professionals as major obstacles included 'adequacy of staff' (34.6%) and 'integration and utilization of information' (26.6%), for example. For surveyors, 'integration and utilization of information' was ranked highest as presenting a major obstacle (43.9%), followed by 'discharge and referral process' (31.7%) and 'medical recording process' (29.3%). The rank orders for the 24 items as problems and major obstacles were similar in both groups (Spearman's rank correlation 0.436, P = 0.033 and 0.583, P = 0.003, respectively). Surveyors had a higher degree of concern and paid more attention to care-related items than health care professionals. CONCLUSIONS: Health care professionals have been facing many problems with multidisciplinary process-related issues of the accreditation standard, whereas surveyors might have had some difficulties in conveying the core QI concepts to them. The findings might be explained by the effects of health care reform on the underlying accreditation principles. One of the strategies to respond to the situation was presented.

Diffusion of Innovation↗
PubMed2004

Avoidance of obstacles in the absence of visual awareness.

The spatial character of our reaching movements is extremely sensitive to potential obstacles in the workspace. We recently found that this sensitivity was retained by most patients with left visual neglect when reaching between two objects, despite the fact that they tended to ignore the leftward object when asked to bisect the space between them. This raises the possibility that obstacle avoidance does not require a conscious awareness of the obstacle avoided. We have now tested this hypothesis in a patient with visual extinction following right temporoparietal damage. Extinction is an attentional disorder in which patients fail to report stimuli on the side of space opposite a brain lesion under conditions of bilateral stimulation. Our patient avoided obstacles during reaching, to exactly the same degree, regardless of whether he was able to report their presence. This implicit processing of object location, which may depend on spared superior parietal-lobe pathways, demonstrates that conscious awareness is not necessary for normal obstacle avoidance.

Brain Injuries↗