Postural effects on biomechanical and psychophysical weight-lifting limits.

Many believe that biomechanical models and data are not sufficiently refined and validated to be used as the basis for setting 'safe' population load lifting limits. Rather, they advocate that such limits should be based on what a sample of the population demonstrate to be 'maximum acceptable weight limits' (MAWL) resulting from psychophysical tests performed with different populations. Yet, biomechanical models are becoming more robust and valid. Computerized versions of these models are readily available, and these models now can provide a more complete understanding of the pathophysiology of a person's spinal column and supporting structures, thereby providing a means to predict the risk of tissue trauma in given lifting situations for large size populations. NIOSH has recognized the validity of both biomechanics and psychophysics for establishing a Recommended Weight Limit (RWL) in the United States. The implications of using both types of methods and data are explored in this paper. Three case studies are presented that involve infrequent lifting of varied size boxes from near floor level to explore how MAWL and biomechanically determined limits differ. The cases include symmetric, sagittal plane lifting using a freestyle posture, a similar lift but with freestyle and squat lift postures, and an asymmetric load lifting task. In all three case comparisons it is shown that a recommended load to be lifted based solely on a spinal disc compression force tolerance of 3400 N would be much lower than published MAWL values representing 75% or even 90% of young males under 40 years old (i.e. MAWL values may not be protective of some young males). It also is shown that MAWL values do not have as much population variance as the spinal motion segment failure values. Hence, many younger males would be expected to have spinal columns that can tolerate the highest published MAWL values. Several mitigating factors, including load lifting trajectories, lifting dynamics, and biomechanical modeling limitations are discussed, as well as differences in compressive force tolerances and MAWLs associated with age and gender.

[1]  A Schultz,et al.  Use of lumbar trunk muscles in isometric performance of mechanically complex standing tasks , 1983, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[2]  R W Norman,et al.  Dynamically and statically determined low back moments during lifting. , 1985, Journal of biomechanics.

[3]  F. Gamberale.  Perceived exertion, heart rate, oxygen uptake and blood lactate in different work operations. , 1972, Ergonomics.

[4]  Stover H. Snook,et al.  The Ergonomics Society The Society's Lecture 1978. THE DESIGN OF MANUAL HANDLING TASKS , 1978 .

[5]  T P Andriacchi,et al.  Influence of dynamic factors on the lumbar spine moment in lifting. , 1988, Ergonomics.

[6]  T P Leskinen,et al.  Comparison of static and dynamic biomechanical models. , 1985, Ergonomics.

[7]  A. Garg,et al.  Maximum acceptable weights and maximum voluntary isometric strengths for asymmetric lifting. , 1986, Ergonomics.

[8]  M M Ayoub,et al.  Manual materials handling capabilities in non-standard postures. , 1992, Ergonomics.

[9]  D. Chaffin,et al.  Biomechanical Stresses as Related to Motion Trajectory of Lifting , 1983, Human factors.

[10]  A. S. Nicholson,et al.  Limitations in the application of materials handling guidelines , 1992 .

[11]  W S Marras,et al.  Quantification of back motion during asymmetric lifting. , 1992, Ergonomics.

[12]  M E Danz,et al.  The effects of speed, frequency, and load on measured hand forces for a floor to knuckle lifting task. , 1992, Ergonomics.

[13]  Hong-ki Kim.  Development of a model for combined ergonomic approaches in manual materials handling tasks , 1990 .

[14]  Maury A. Nussbaum,et al.  A geometric model of the human torso , 1991 .

[15]  D B Chaffin,et al.  A biomechanical evaluation of five lifting techniques. , 1986, Applied ergonomics.

[16]  S H Snook,et al.  The design of manual handling tasks: revised tables of maximum acceptable weights and forces. , 1991, Ergonomics.

[17]  Richard Evan Hughes,et al.  Empirical evaluation of optimization-based lumbar muscle force prediction models. , 1991 .

[18]  A Luttmann,et al.  The load on the lumbar spine during asymmetrical bi-manual materials handling. , 1992, Ergonomics.

[19]  Park KyungS.,et al.  A Biomechanical Evaluation of Two Methods of Manual Load Lifting , 1974 .

[20]  W Karwowski,et al.  Reliability of the psychophysical approach to manual lifting of liquids by females. , 1986, Ergonomics.

[21]  A Garg,et al.  An evaluation of the NIOSH guidelines for manual lifting, with special reference to horizontal distance. , 1989, American Industrial Hygiene Association journal.

[22]  F Aghazadeh,et al.  Evaluating lifting tasks using subjective and biomechanical estimates of stress at the lower back. , 1991, Ergonomics.

[23]  S H Snook,et al.  Maximum weights and work loads acceptable to male industrial workers. A study of lifting, lowering, pushing, pulling, carrying, and walking tasks. , 1970, American Industrial Hygiene Association journal.

[24]  W Karwowski,et al.  Psychophysical acceptability and perception of load heaviness by females. , 1991, Ergonomics.

[25]  G. Andersson,et al.  Electromyographic studies of the lumbar trunk musculature during the development of axial torques , 1986, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[26]  Don B. Chaffin,et al.  Shear force considerations in predicting torso muscle antagonism , 1987 .

[27]  Anil Mital,et al.  Development of Strength and Capacity Norms for Manual Materials Handling Activities: The State of the Art , 1980 .

[28]  A B Schultz,et al.  A model for semi-quantitative studies of muscle actions. , 1979, Journal of biomechanics.

[29]  S. Snook,et al.  Maximum acceptable weight of lift. , 1967, American Industrial Hygiene Association journal.

[30]  A. S. Nicholson,et al.  A comparative study of methods for establishing load handling capabilities. , 1989, Ergonomics.

[31]  P. Brinckmann,et al.  Fatigue fracture of human lumbar vertebrae. , 1988, Clinical biomechanics.

[32]  M. M. Ayoub,et al.  Problems and solutions in manual materials handling: the state of the art , 1992 .

[33]  A. Mital.  Maximum weights of lift acceptable to male and female industrial workers for extended work shifts. , 1984, Ergonomics.

[34]  William S. Marras.  Trunk motion during lifting: Temporal relations among loading factors , 1987 .

[35]  R W Norman,et al.  Measurement of the trunk musculature of active males using CT scan radiography: implications for force and moment generating capacity about the L4/L5 joint. , 1988, Journal of biomechanics.

[36]  T Belytschko,et al.  A model for studies of mechanical interactions between the human spine and rib cage. , 1974, Journal of biomechanics.

[37]  M. Adams,et al.  Can the Lumbar Spine Be Crushed in Heavy Lifting? , 1982, Spine.

[38]  L. S. Matthews,et al.  A biomechanical model of the lumbosacral joint during lifting activities. , 1985, Journal of biomechanics.

[39]  Don B. Chaffin,et al.  BIOMECHANICAL COMPUTERIZED SIMULATION OF HUMAN STRENGTH. , 1974 .

[40]  D B Chaffin,et al.  A dynamic biomechanical evaluation of lifting maximum acceptable loads. , 1984, Journal of biomechanics.

[41]  E N Corlett,et al.  A technique for assessing postural discomfort. , 1976, Ergonomics.

[42]  A B Schultz,et al.  Biomechanical model calculation of muscle contraction forces: a double linear programming method. , 1988, Journal of biomechanics.

[43]  A Mital,et al.  Margin of safety for the human back: a probable consensus based on published studies. , 1992, Ergonomics.