Disturbances of grip force behaviour in focal hand dystonia: evidence for a generalised impairment of sensory-motor integration? (73/202)

BACKGROUND: Focal task specific dystonia occurs preferentially during performance of a specific task. There may be an inefficiently high grip force when doing manipulative tasks other than the trigger task, possibly reflecting a generalised impairment of sensory-motor integration. OBJECTIVE: To examine how well subjects with writer's cramp (n = 4) or musician's cramp (n = 5) adapted their grip force when lifting a new object or catching a weight. METHODS: Nine patients with focal hand dystonia and 10 controls were studied. Experiments addressed different motor behaviours: (A) lifting and holding an object; (B) adjusting grip force in anticipation of or in reaction to a change in load force by catching a small weight dropped expectedly or unexpectedly into a hand held receptacle. RESULTS: In (A), patients produced a grip force overshoot during the initial lifts; force overflow was most pronounced in those with writer's cramp. Patients and controls adjusted their grip force to object weight within one or two lifts, though patients settled to a steady force level above normal. In (B), patients with focal hand dystonia and normal controls showed similar predictive grip force adjustments to expected changes in object load, suggesting that this aspect of sensory-motor integration was normal. Patients had a shorter latency of grip force response than controls after an unexpected load increase, reflecting either a greater level of preparatory motor activity or a disinhibited spinal reflex response. CONCLUSIONS: The overall increased grip force in patients with focal hand dystonia is likely to be a prelearned phenomenon rather than a primary disorder of sensory-motor integration.  (+info)

Kinematic cues in perceptual weight judgement and their origins in box lifting. (74/202)

When accepting a parcel from another person, we are able to use information about that person's movement to estimate in advance the weight of the parcel, that is, to judge its weight from observed action. Perceptual weight judgment provides a powerful method to study our interpretation of other people's actions, but it is not known what sources of information are used in judging weight. We have manipulated full form videos to obtain precise control of the perceived kinematics of a box lifting action, and use this technique to explore the kinematic cues that affect weight judgment. We find that observers rely most on the duration of the lifting movement to judge weight, and make less use of the durations of the grasp phase, when the box is first gripped, or the place phase, when the box is put down. These findings can be compared to the kinematics of natural box lifting behaviour, where we find that the duration of the grasp component is the best predictor of true box weight. The lack of accord between the optimal cues predicted by the natural behaviour and the cues actually used in the perceptual task has implications for our understanding of action observation in terms of a motor simulation. The differences between perceptual and motor behaviour are evidence against a strong version of the motor simulation hypothesis.  (+info)

Role of intra-abdominal pressure in the unloading and stabilization of the human spine during static lifting tasks. (75/202)

The role of intra-abdominal pressure (IAP) in unloading the spine has remained controversial. In the current study, a novel kinematics-based approach along with a nonlinear finite-element model were iteratively used to calculate muscle forces, spinal loads, and stability margin under prescribed postures and loads measured in in vivo studies. Four coactivity levels (none, low, moderate, and high) of abdominal muscles (rectus abdominis, external oblique, and internal oblique) were considered concurrently with a raise in IAP from 0 to 4 kPa when lifting a load of 180 N in upright standing posture and to 9 kPa when lifting the same load in forward trunk flexions of 40 degrees and 65 degrees. For comparison, reference cases with neither abdominal coactivity nor IAP were investigated as well. A raise in IAP unloaded and stabilized the spine when no coactivity was considered in the foregoing abdominal muscles for all lifting tasks regardless of the posture considered. In the upright standing posture, the unloading action of IAP faded away even in the presence of low level of abdominal coactivity while its stabilizing action continued to improve as abdominal coactivity increased to moderate and high levels. For lifting in forward-flexed postures, the unloading action of IAP disappeared only with high level of abdominal coactivities while its stabilizing action deteriorated as abdominal coactivities increased. The unloading and stabilizing actions of IAP, hence, appear to be posture and task specific.  (+info)

The role of physical workload and pain related fear in the development of low back pain in young workers: evidence from the BelCoBack Study; results after one year of follow up. (76/202)

AIMS: To study the influence of work related physical and psychosocial factors and individual characteristics on the occurrence of low back pain among young and pain free workers. METHODS: The Belgian Cohort Back Study was designed as a prospective cohort study. The study population of this paper consisted of 716 young healthcare or distribution workers without low back pain lasting seven or more consecutive days during the year before inclusion. The median age was 26 years with an interquartile range between 24 and 29 years. At baseline, these workers filled in a questionnaire with physical exposures, work related psychosocial factors and individual characteristics. One year later, the occurrence of low back pain lasting seven or more consecutive days and some of its characteristics were registered by means of a questionnaire. To assess the respective role of predictors at baseline on the occurrence of low back pain in the following year, Cox regression with a constant risk period for all subjects was applied. RESULTS: After one year of follow up, 12.6% (95% CI 10.1 to 15.0) of the 716 workers had developed low back pain lasting seven or more consecutive days. An increased risk was observed for working with the trunk in a bent and twisted position for more than two hours a day (RR 2.2, 95% CI 1.2 to 4.1), inability to change posture regularly (RR 2.1, 95% CI 1.3 to 3.5), back complaints in the year before inclusion (RR 1.7, 95% CI 1.1 to 2.8), and high scores of pain related fear (RR 1.8, 95% CI 1.0 to 3.1). Work related psychosocial factors and physical factors during leisure time were not predictive. CONCLUSION: This study highlighted the importance of physical work factors and revealed the importance of high scores of pain related fear in the development of low back pain among young workers.  (+info)

Correlates of return to work for breast cancer survivors. (77/202)

PURPOSE: To identify correlates of return to work for employed breast cancer survivors. PATIENTS AND METHODS: Patients included 416 employed women with newly diagnosed breast cancer identified from the Metropolitan Detroit Cancer Surveillance System. Patients were interviewed by telephone 12 and 18 months after diagnosis. Correlates of return to work at 12 and 18 months were identified using multivariate logistic regression. RESULTS: More than 80% of patients returned to work during the study period, and 87% reported that their employer was accommodating to their cancer illness and treatment. After adjusting for demographic characteristics, health status, cancer stage, treatment, and job type, heavy lifting on the job (odds ratio = 0.42; 95% CI, 0.18 to 0.99), perceived employer accommodation for cancer illness and treatment (odds ratio = 2.2; 95% CI, 1.03 to 4.8), and perceived employer discrimination because of a cancer diagnosis (odds ratio = 0.27; 95% CI, 0.10 to 0.71) were independently associated with return to work at 12 months after breast cancer diagnosis, and perceived employer accommodation (odds ratio = 2.3; 95% CI, 1.06 to 5.1) was independently associated with return to work at 18 months after breast cancer diagnosis. CONCLUSION: A high percentage of employed breast cancer patients returned to work after treatment, and workplace accommodations played an important role in their return. In addition, perceived employer discrimination because of cancer was negatively associated with return to work for breast cancer survivors. Employers seem to have a pivotal role in breast cancer patients' successful return to work.  (+info)

Reproducibility and validity of workers' self-reports of physical work demands. (78/202)

The objective of this paper is to provide a systematic review of the reproducibility and validity of self-report questions concerning physical work demands. After a bibliographic search of Medline and Ergonomic Abstracts for 1980-2003, 15 articles meeting the eligibility criteria were reviewed for methodological quality; 82 formulations of questions on physical work demands were evaluated for reproducibility and 83 for validity. Questions evaluated for both reproducibility and validity that performed well in both sets of studies included those on duration or presence of sitting and standing posture, the presence of walking, kneeling or squatting postures, duration or frequency of hands above shoulders, manual handling of more than or less than 10 kg, general level of physical effort, presence and duration of whole-body vibration, and duration of the use of visual display terminals. Suggestions for improving the design of reproducibility and validity studies and directions for future research in physical workload measurement are proposed.  (+info)

Physical work environment risk factors for long term sickness absence: prospective findings among a cohort of 5357 employees in Denmark. (79/202)

OBJECTIVES: To examine the effects of physical work environment on long term sickness absence and to investigate interaction between physical and psychosocial risk factors. DESIGN AND SETTING: Prospective cohort study of long term sickness absence among employees in Denmark. PARTICIPANTS: 5357 employees interviewed in 2000 about their physical work environment, and various covariates were followed for 18 months in a national sickness absence register. Outcome measurements Cox regression analysis was performed to assess risk estimates for physical risk factors in the work environment and onset of long term sickness absence, defined as receiving sickness absence compensation for eight consecutive weeks or more. RESULTS: 348 participants (6.9%) developed long term sickness absence during follow-up. Of these, 194 (55.7%) were women and 154 (44.3%) were men. For both female and male employees, risk of onset of long term sickness absence was increased by extreme bending or twisting of the neck or back, working mainly standing or squatting, lifting or carrying loads, and pushing or pulling loads. Significant interactions were found for three combinations of physical and psychosocial work environment risk factors among female employees (P<0.05). CONCLUSION: Uncomfortable working positions, lifting or carrying loads, and pushing or pulling loads increased the risk of onset of long term sickness absence. The study shows a potential for reducing long term sickness absence through modifying work postures straining the neck and back, reducing the risk of work done standing or walking, and reducing the risk associated with handling loads. Dealing with psychosocial stressors simultaneously may improve physical intervention efforts further for female employees.  (+info)

Interface stability influences torso muscle recruitment and spinal load during pushing tasks. (80/202)

Handle or interface design can influence torso muscle recruitment and spinal load during pushing tasks. The objective of the study was to provide insight into the role of interface stability with regard to torso muscle recruitment and biomechanical loads on the spine. Fourteen subjects generated voluntary isometric trunk flexion force against a rigid interface and similar flexion exertions against an unstable interface, which simulated handle design in a cart pushing task. Normalized electromyographic (EMG) activity in the rectus abdominus, external oblique and internal oblique muscles increased with exertion effort. When using the unstable interface, EMG activity in the internal and external oblique muscle groups was greater than when using the rigid interface. Results agreed with trends from a biomechanical model implemented to predict the muscle activation necessary to generate isometric pushing forces and maintain spinal stability when using the two different interface designs. The co-contraction contributed to increased spinal load when using the unstable interface. It was concluded that handle or interface design and stability may influence spinal load and associated risk of musculoskeletal injury during manual materials tasks that involve pushing exertions.  (+info)