Mechanisms for age-related changes of fingertip forces during precision gripping and lifting in adults.
We investigated changes across the adult life span of the fingertip forces used to grip and lift objects and their possible causes. Grip force, relative safety margin (grip force exceeding the minimum to avoid slip, as a fraction of slip force), and skin slipperiness increased beginning at age 50 years. Skin slipperiness explained relative safety margin increases until age 60 years. Hence, after age 60 years, additional factors must elevate grip force. We argue that one factor is impaired cutaneous afferent encoding of skin-object frictional properties on the basis of three findings. First, only subjects 60 years and older increased their relative safety margins when the friction of the gripped surfaces was varied randomly versus experiments that varied only object weight. Skin slipperiness did not account for this behavior. Second, these older subjects scaled the initial portion of their force trajectories for the slippery surface during experiments when friction was varied. Third, their grip force adjustments to new surfaces were delayed approximately 100 msec as compared with young subjects. Previous research has demonstrated that friction is signaled locally by fast-adapting afferents (FA I afferents), which decrease in number during old age. By contrast, adjustments triggered by object set-down, an event encoded by FA II afferents throughout the hand and wrist, were not delayed in our old subjects. Other findings included that anticipatory control of fingertip forces using memory of object weight was unimpaired in old age. Finally, old and young adults modulated their fingertip forces with equal smoothness and with similar relative intertrial variability. (+info)
Is there a rational basis for post-surgical lifting restrictions? 1. Current understanding.
Lifting restrictions postoperatively are quite common, but there appears to be little scientific basis for them. Lifting restrictions are inhibitory in terms of return to work and may be a factor in chronicity. The mean functional spinal motion unit stiffness changes with in vitro or computer-simulated discectomies, facetectomies and laminectomies were reviewed from the literature. We modified the NIOSH lifting equation to include another multiplier related to stiffness change post surgery. The new recommended lifts were computed for different lifting conditions seen in industry. The reduction of rotational stiffness ranged from 21% to 41% for a discectomy, 1% to 59% for a facetectomy and 4% to 16% for a partial laminectomy. The recommended lifts based on our modified equation were adjusted accordingly. There is no rational basis for current lifting restrictions. The risk to the spine is a function of many other variables as well as weight (i.e., distance of weight from body). The adjusted NIOSH guidelines provide a reasonable way to estimate weight restrictions and accommodations such as lifting aids. Such restrictions should be as liberal as possible so as to facilitate, not prevent, return to work. Patients need more advice regarding lifting activities and clinicians should be more knowledgeable about the working conditions and constraints of a given workplace to effectively match the solution to the patient's condition. (+info)
Is there a rational basis for post-surgical lifting restrictions? 2. Possible scientific approach.
Lifting restrictions postoperatively are quite common but there appears to be little scientific basis for them. Lifting restricitions are inhibitory in terms of return to work and may be a factor in chronicity. The mean changes in functional spinal motion unit (FSU) stiffness with in vitro or computer-simulated discectomies, facetectomies and laminectomies were reviewed from the literature. We modified the NIOSH lifting equation to include another multiplier related to stiffness change post surgery. The new recommended lifts were computed for different lifting conditions seen in industry. The reduction of rotational stiffness ranged from 21% to 41% for a discectomy, 1% to 59% for a facetectomy and 4% to 16% for a partial laminectomy. The recommended lifts based on our modified equation were adjusted accordingly. There is no rational basis for current lifting resctrictions. The risk to the spine is a function of many other variables as well as weight (i.e., distance of weight from body). The adjusted NIOSH guidelines provide a reasonable way to estimate weight restrictions and accomodations such as lifting aids. Such resitrictions should be as liberal as possible so as to facilitate, not prevent, return to work. Patients need more advice regarding lifting activities and clinicians should be more knowledgeable about the working conditions and constraints of a given workplace to effectively match the solution to the patient's condition. (+info)
Association of low back pain with self-reported risk factors among patients seeking physical therapy services.
BACKGROUND AND PURPOSE: This study investigated the magnitude of association between low back pain (LBP) and self-reported factors thought to increase the risk of LBP. SUBJECTS AND METHODS: Questionnaires were completed by 150 patients who were receiving physical therapy for LBP and by 138 patients who were being treated for other reasons. The solicited information was used to estimate odds ratios and 95% confidence intervals for the LBP-risk factor association. RESULTS: Low back pain was positively associated with smoking status, pregnancy, industrial vibration exposure, and time spent in a car (odds ratios > or = 2.21). Daily lifting, body mass index, activity level, and time sitting or standing showed at most a weak positive association with LBP. Comparisons with estimated associations from other studies were made. CONCLUSION AND DISCUSSION: Data from this study support a statistically significant association between LBP and some factors found in other research to increase the risk of LBP. Study findings may have implications for targeting at-risk groups for back care education or intervention programs. (+info)
Smoking, heavy physical work and low back pain: a four-year prospective study.
Data from a community-based four-year prospective study were used to test the hypothesis that heavy physical work is a stronger predictor of low back pain in smokers than in non-smokers. Of 708 working responders without low back pain during the entire year prior to 1990, 562 (79%) completed a questionnaire four years later in 1994. A job involving heavy lifting and much standing in 1990 was a strong predictor of low back pain in smokers four years later [odds ratio (OR) = 5.53, 95% confidence interval (CI) = 1.93-15.84, p < 0.01) after having adjusted for other job characteristics, demographic factors, emotional symptoms, physical exercise and musculoskeletal pain elsewhere. In non-smokers, having a job with heavy lifting and much standing was not associated with low back pain. One explanation may be that smoking leads to reduced perfusion and malnutrition of tissues in or around the spine and causes these tissues to respond inefficiently to mechanical stress. (+info)
Risk factors for back injury in 31,076 retail merchandise store workers.
Risk factors for work-associated strain or sprain back injuries were investigated in a cohort of 31,076 material handlers from 260 retail merchandise stores in the United States. The workers studied were those with significant material-handling responsibilities--daily lifting and movement of merchandise. Workers in jobs with the greatest physical work requirements had an injury rate of 3.64 per 100 person-years versus 1.82 in workers with lesser work requirements. The unadjusted injury rate for males was 3.67 per 100 person-years compared with 2.34 per 100 person-years for females, but the excess for males was confounded by higher physical work requirements for men in the stocker/receiver job category. The injury rate ratio for short versus long duration of employment was 3.53 (95% confidence interval: 2.90, 4.30); for medium versus long duration of employment, it was 1.38 (95% confidence interval: 1.18, 1.62). The elevated rate ratios were maintained when the data were stratified by subsets with different rates of turnover. The results suggest that workers with the greatest physical work requirements and those with the shortest duration of employment are at the highest risk of back injuries. However, selection forces causing worker turnover within this cohort of active workers are not well characterized and have the potential to bias the measures for time-related factors such as duration of employment. (+info)
Comparison of four peak spinal loading exposure measurement methods and their association with low-back pain.
OBJECTIVES: This paper examines the performance of 4 different methods of estimating peak spinal loading and their relationship with the reporting of low-back pain. METHODS: The data used for this comparison was a subset of subjects from a case-referent study of low-back-pain reporting in the automotive industry, in which 130 random referents and 105 cases (or job-matched proxies) were studied. The peak load on the lumbar spine was determined using a biomechanical model with model inputs coming from a detailed self-report questionnaire, a task-based check list, a video digitization method, and a posture and load sampling technique. RESULTS: The methods were directly comparable through a common metric of newtons or newton meters of spinal loading in compression, shear, or moment modes. All the methods showed significant and substantial associations with low-back pain in all modes (odds ratios 1.6-2.3). The intraclass correlation coefficients (ICC) showed strong similarities between the checklist and video digitized techniques (ICC 0.84-0.91), moderate similarities between these techniques and the work sampling method (ICC 0.49-0.52), and poor correlations (ICC 0.16-0.40) between the self-report questionnaire and the observer recorded measures. CONCLUSIONS: While all the methods detected significant odds ratios, they cannot all be used interchangeably for risk assessment at the individual level. Peak spinal compression, moment, and shear are important risk factors for low-back pain reporting, no matter which measurement method is used. Questionnaires can be used for large-scale studies. At the individual level a task-based checklist provides biomechanical model inputs at lower cost and equal performance compared with the criterion video digitization system. (+info)
Retrospective versus original information on physical and psychosocial exposure at work.
OBJECTIVES: Retrospective exposure assessments are often performed in epidemiologic studies. The presence of an eventual misclassification, both nondifferential and differential, is debated but can rarely be investigated. The aim of this study was to compare self-reported information on the same physical and psychosocial work exposures with 25 years' difference. METHODS: In 1969-1970 a survey of randomly chosen men and women in Stockholm county, concerning, among other things, work exposures, was undertaken. During 1993-1994, 280 subjects participated in a reexamination, regarding psychosocial and physical factors at work and musculoskeletal disorders. The questions were all formulated in the same way as in 1969-1970. RESULTS: When self-reported information on work exposures, collected with a 25-year interval, was compared, acceptable, although not high, agreement was found for 3 out of 4 physical factors and for 4 out of 10 physical environmental factors. Questions measuring psychosocial load had somewhat lower agreement. Current exposure status influenced the memory of past exposures. Study subjects who reported low-back disorders at the reexamination tended to show a better agreement in their assessments of retrospective exposures than those without current symptoms. When relative risks from original and retrospective data were calculated, hardly any influence on the estimates due to that differential misclassification could be found. For persons with and without neck or shoulder symptoms no apparent differences in assessments were found. CONCLUSIONS: Retrospective assessments of exposures at the workplace showed misclassifications to a certain degree. However, the influence of the misclassifications on the risk estimates was limited. (+info)