M.J.M. Hoozemans

Stoop or squat: a review of biomechanical studies on lifting technique

OBJECTIVE To assess the biomechanical evidence in support of advocating the squat lifting technique as an administrative control to prevent low back pain. BACKGROUND Instruction with respect to lifting technique is commonly employed to prevent low back pain. The squat technique is the most widely advised lifting technique. Intervention studies failed to show health effects of this approach and consequently the rationale behind the advised lifting techniques has been questioned. METHODS Biomechanical studies comparing the stoop and squat technique were systematically reviewed. The dependent variables used in these studies and the methods by which these were measured or estimated were ranked for validity as indicators of low back load. RESULTS Spinal compression as indicated by intra-discal pressure and spinal shrinkage appeared not significantly different between both lifting techniques. Net moments and compression forces based on model estimates were found to be equal or somewhat higher in squat than in stoop lifting. Only when the load could be lifted from a position in between the feet did squat lifting cause lower net moments, although the studies reporting this finding had a marginal validity. Shear force and bending moments acting on the spine appeared lower in squat lifting. Net moments and compression forces during lifting reach magnitudes, that can probably cause injury, whereas shear forces and bending moments remained below injury threshold in both techniques. CONCLUSION The biomechanical literature does not provide support for advocating the squat technique as a means of preventing low back pain. RELEVANCE Training in lifting technique is widely used in primary and secondary prevention of low back pain, though health effects have not been proven. The present review assesses the biomechanical evidence supporting the most widely advocated lifting technique.

Local dynamic stability and variability of gait are associated with fall history in elderly subjects

Gait parameters that can be measured with simple instrumentation may hold promise for identifying individuals at risk of falling. Increased variability of gait is associated with increased risk of falling, but research on additional parameters indicates that local dynamic stability (LDS) of gait may also be a predictor of fall risk. The objective of the present study was to assess the association between gait variability, LDS of gait and fall history in a large sample of elderly subjects. Subjects were recruited and tested at a large national fair. One hundred and thirty four elderly, aged 50-75, who were able to walk without aids on a treadmill, agreed to participate. After subjects walked on a treadmill, LDS (higher values indicate more instability) and variability parameters were calculated from accelerometer signals (trunk worn). Fall history was obtained by self-report of falls in the past 12 months. Gait variability and short-term LDS were, individually and combined, positively associated with fall history. In conclusion, both increased gait variability and increased short-term LDS are possible risk factors for falling in the elderly.

The relationship between overweight and obesity, and sick leave: a systematic review

Objective:To investigate the relationship between overweight and obesity and sick leave.Design:Systematic, qualitative review.Literature search:A search in diverse databases was performed. Studies were considered as relevant if they were longitudinal in design and investigated the relationship between overweight and obesity and sick leave.Data extraction:The methodological quality of the studies was evaluated with a quality criteria list. To draw conclusions, a best-evidence synthesis was applied.Results:Thirteen studies were included. Four out of seven found overweight to be a predictor of long-term sick leave, whereas the remaining three showed a positive trend, but did not observe significance. Of the five studies investigating the relationship between overweight and short-term sick leave, inconsistent results were shown. Seven out of eight studies investigating the relationship with long-term sick leave found obesity as a significant predictor of long-term sick leave. In contrast, there were inconsistent results between the five studies examining the relationship between obesity and short spells of sick leave.Conclusions:Although this review found inconclusive evidence for a relationship between overweight and sick leave, a clear trend was discerned in that overweight was a predictor of especially long spells (>7 days) of sick leave. As regards obesity, there was strong evidence for a positive relationship with sick leave because of the consistent finding that obesity was a significant predictor of long-term sick leave.

Mechanical loading of the low back and shoulders during pushing and pulling activities

The objective of this study was to quantify the mechanical load on the low back and shoulders during pushing and pulling in combination with three task constraints: the use of one or two hands, three cart weights, and two handle heights. The second objective was to explore the relation between the initial and sustained exerted forces and the mechanical load on the low back and shoulders. Detailed biomechanical models of the low back and shoulder joint were used to estimate mechanical loading. Using generalized estimating equations (GEE) the effects were quantified for exerted push/pull forces, net moments at the low back and shoulders, compressive and shear forces at the low back, and compressive forces at the glenohumeral joint. The results of this study appeared to be useful to estimate ergonomics consequences of interventions in the working constraints during pushing and pulling. Cart weight as well as handle height had a considerable effect on the mechanical load and it is recommended to maintain low cart weights and to push or pull at shoulder height. Initial and sustained exerted forces were not highly correlated with the mechanical load at the low back and shoulders within the studied range of the exerted forces.

Pushing and pulling in association with low back and shoulder complaints

Aims: To examine the association between exposure to pushing/pulling at work and low back and shoulder complaints. Methods: A cross sectional questionnaire survey was carried out among 434 workers from several companies with mainly pushing/pulling tasks. From the same companies 188 workers without physically demanding tasks served as reference. The questionnaire was used to assess the exposure to pushing/pulling and other physical risk factors for low back and shoulder complaints. Mean scores at company level were used to classify groups into medium and high exposed to pushing/pulling and a reference group. Psychosocial factors at work were also assessed. Several pain related questionnaires were used to assess the 12 month prevalence of low back and shoulder complaints in three dimensions: trouble (ache, pain, discomfort), pain intensity, and disability. Prevalence rate ratios (PRs) were calculated using Cox’s proportional hazards regression analysis. Results: The 12 month prevalence of low back complaints was almost equal for all three groups. The prevalence of shoulder complaints increased with an increase in exposure level. Adjusted PRs showed that the high exposed group had an increased risk for low back complaints compared to the reference group. For all dimensions of shoulder complaints a clear tendency towards a dose–response relation was observed. The high exposed group had significant PRs for shoulder complaints, ranging from 2.09 to 6.37. Generally, psychosocial factors had a confounding effect for pain intensity and disability, but not for trouble. Conclusions: For shoulder complaints a dose–response relation was observed for exposure to pushing/pulling. Low back complaints were less consistently associated with pushing/pulling. Stronger associations were observed for more severe cases of low back and shoulder complaints. It is hypothesised that work related psychosocial factors affect these associations.

Assessment of exposure to pushing and pulling in epidemiological field studies: an overview of methods, exposure measures, and measurement strategies

Abstract Although pushing and pulling is very common in occupational settings, this type of manual materials handling is less well studied than lifting and carrying. Several issues should be considered when obtaining exposure measures in epidemiological field studies on pushing and pulling. The purpose of this article is threefold: (i) to critically evaluate different methods to assess push and pull forces, (ii) to describe measures of exposure to pushing and pulling, and (iii) to consider measurement strategies for assessment of exposure to pushing and pulling. Firstly, information on the level of exerted forces with the accuracy needed for epidemiology can only be obtained from direct measurement methods. These methods are particularly required when push and pull tasks are biomechanically analysed, implying that also force direction and point of application relative to the worker have to be assessed. Secondly, to obtain a limited number of external exposure measures that reflect exposure to pushing and pulling over time, aggregation of various force measurements is suggested. Internal exposure measures and parameters corresponding to guidelines are also described. Thirdly, for truck drivers and refuse collectors a strategy of approximately five repeated measurements for each representative working situation is advised to obtain a reliable estimate of an individuals exposure to pushing and pulling. Relevance to industry An overview is given of methods to assess forces accompanying pushing and pulling, which are very common activities in industry. Examples of exposure measures and measurement strategies in studies on adverse health effects of pushing and pulling are presented. Such studies should eventually stimulate prevention of work-related musculoskeletal disorders.

Gender differences in exerted forces and physiological load during pushing and pulling of wheeled cages by postal workers.

The aim was to determine gender differences regarding exerted forces and physiological load during push/pull tasks simulating the daily working practice of postal workers. Eight female and four male workers handled four-wheeled cages under eight conditions corresponding to the cage weight (130, 250, 400, 550 kg) and the direction of force exertion (pushing, pulling). For each of the five dependent variables, average force, initial force, ending force, oxygen uptake and heart rate, two analyses of variance with repeated measurements were performed, i.e. with and without correction for the workers body weight, body height and maximum capacity regarding the dependent variable. Exerted forces and physiological load were high for the cages weighing 400 and 550 kg. Gender differences were significant for all dependent variables (p=0.030-0.000). When the personal factors were included in the model, male workers exerted significantly higher average forces and ending forces than their females, while differences regarding initial forces and physiological load were not significant. However, none of the personal factors were significantly related to any of the dependent variables. It is concluded that gender differences in exerted forces were not caused by differences in anthropometry and maximum capacity, but due to application of different work methods by women in order to balance work demands and work ability.

Effect of lifting height and load mass on low back loading

The objective of this study was to quantify the effect of lifting height and mass lifted on the peak low back load in terms of net moments, compression forces and anterior–posterior shear forces. Ten participants had to lift a box using four handle heights. Low back loading was quantified using a dynamic 3-D linked segment model and a detailed electromyographic driven model of the trunk musculature. The effects of lifting height and lifting mass were quantified using a regression technique (GEE) for correlated data. Results indicate that an increase in lifting height and a decrease in lifting mass were related to a decrease in low back load. It is argued that trunk flexion is a major contributor to low back load. For ergonomic interventions it can be advised to prioritise optimisation of the vertical location of the load to be lifted rather than decreasing the mass of the load for handle heights between 32 cm and 155 cm, and for load masses between 7.5 and 15 kg. Lifting height and load mass are important determinants of low back load during manual materials handling. This paper provides the quantitative effect of lifting height and mass lifted, the results of which can be used by ergonomists at the workplace to evaluate interventions regarding lifting height and load mass.

Optimizing the determination of the body center of mass.

The position or trajectory of the body center of mass (COM) is often a parameter of interest when studying posture or movement. For instance, in balance control studies the body COM can be related to the ground reaction force or to the base of support. Since small displacements of the body COM are important in balance control studies, it is essential to obtain valid estimates of the body COM. The main source of error in the determination of the body COM is the estimation of the masses and centers of mass of the body segments. Especially the determination of the trunk COM is prone to error. In the current study five subjects maintained three postures, differing in trunk angle, during a few seconds. The relation between the center of pressure of the ground reaction force and the vertical projection of the body COM during the postures was used to optimize the trunk COM position. Additionally the subjects performed two lifting movements. The validity of the body COM trajectory estimation during the lifting movements, both with and without optimized trunk COM, was checked by relating the external moment of the ground reaction force with respect to the body COM to the rate of change of the angular momentum of the whole body. It was shown that the correspondence between the external moment and the rate of change of the angular momentum improved after optimization of the trunk COM. This suggests that the body COM trajectory estimation can be improved by the proposed optimization procedure.

Effectiveness of a Multidisciplinary Occupational Training Program for Chronic Low Back Pain

Koopman FS, Edelaar M, Slikker R, Reynders K, van der Woude LHV, Hoozemans MJM: Effectiveness of a multidisciplinary occupational training program for chronic low back pain: A prospective cohort study. Am J Phys Med Rehabil 2004;83:94–103. ObjectiveTo evaluate the effectiveness of a 12-wk multidisciplinary occupational training program for patients with chronic low back pain and to identify prognostic factors for treatment success. DesignA total of 51 participants were evaluated at baseline, at discharge, and at 1 yr after conclusion of the program. The evaluation included a physical examination and assessment of functional disability, psychological factors, and coping styles. The main target of the program is full work resumption. The central outcome measures therefore are three variables on return to work. ResultsAnalysis of variance for repeated measures revealed significant beneficial changes during the program for all measures except for several coping-style variables. The acquired level of maximum oxygen uptake, trunk flexibility, functional disability, and catastrophizing were maintained at 1-yr follow-up. At 1-yr follow-up, >60% of the participants had fully returned to work, which is an increase of >40% compared with baseline. Regression analyses showed that sex, age, the baseline values of reinterpretation of pain sensations, and functional disability and changes in trunk flexibility scores during the program are important prognostic factors for complete return to work. ConclusionsBased on the current findings, the program seems to be efficacious in the short term. Future attention must be directed toward maintaining these results, although work resumption rates improved considerably 1 yr after conclusion of the program.