2008 ISEK Congress Keynote LectureOccupational spine biomechanics: A journey to the spinal frontier
Introduction
It is well known that spine injuries, most often in the lower back, are prevalent in the workplace. Many researchers in the discipline of occupational biomechanics have dedicated themselves to furthering our knowledge of the mechanical characteristics of the spine and its neural control, so that we might further understand its normal function during manual materials handling (MMH) tasks and potential mechanisms of injury. This paper will provide a very brief overview of the various fields of emphasis in occupational spine biomechanics. While an attempt will be made to provide some historical context to the development of this field, this paper is certainly not a comprehensive history of the vast and impressive variety of research published on this topic. Rather, an effort will be made to introduce the main areas of emphasis, while citing some of the earliest pioneering work. Where relevant, some of our own research will be integrated into this paper. However, this certainly does not presume that they have had the same impact as the landmark studies also cited.
Section snippets
Acute loading
For decades, lumbar intervertebral disc compression force was the main variable of interest when assessing low back injury (LBI) risk in the workplace. NIOSH (1981) integrated biomechanical and epidemiological data and recommended a compression force Action Limit of 3400 N. Jager and Luttmann (1991) and Genaidy et al. (1993) have presented predictive models for further delineating compression force tolerance based on variables like gender, age, percentile, lumbar level etc. While much of the
Direct measures
Nachemson and Morris (1964) inserted a pressure–sensitive needle into L3/4 intervertebral discs to determine the effects of various static loading trials. While later efforts were made to convert these pressures to compression force (Nachemson, 1981), they did not actually represent direct measures. In fact, it is not currently possible to make such direct in vivo measurements of spine tissue loading.
Simple biomechanical models
Given the infeasibility of direct spine load measures, biomechanical models were developed to
Early studies
Some of the earliest trunk loading studies were conducted, first with no hand loads (Floyd and Silver, 1951, Floyd and Silver, 1955) and then while subjects supported external loads (Whitney, 1958, Grieve, 1958, Davis, 1959). Davis (1959) presented one of the first concepts of an internal single equivalent muscle model and Floyd and Silver (1955) published EMG records indicating the flexion–relaxation phenomenon for the first time.
Lifting and lowering
Since the early-1950’s, lifting and lowering has been the
Prolonged or repetitive spine loading
Almost all of the early occupational biomechanics research on MMH was focused on acute loading and tissue damage. Early research related to repetitive load handling was concerned more with physiological cost and fatigue (e.g. Jorgensen and Poulsen, 1974, Legg and Myles, 1981), and not tissue injury implications. One of the first studies of the mechanical consequences of repetitive spine loading was performed by Parnianpour et al. (1988). They had subjects perform repetitive, isodynamic trunk
Ergonomic assessment tools
Some of the earliest work to establish safe limits for manual materials handling was performed at Liberty Mutual Insurance (e.g. Snook and Irvine, 1966, Snook and Irvine, 1967). This large series of studies culminated in the “Liberty Mutual” or “Snook” tables (Snook and Ciriello, 1991). Ayoub and colleagues presented a large number of equations for predicting MMH capacity based on a set of measured task variables (e.g. Ayoub et al., 1978). Garg et al. (1978) presented equations to predict the
Sudden/unexpected loading
Magora (1973) was among the first to demonstrate a relationship between sudden trunk loading and the prevalence of low back pain (LBP). Since that time, a number of researchers have made substantial contributions to our understanding of the response of the spine to sudden loading and unloading, and the potential mechanical contributions this might make to spine tissue injury (see Carlson et al., 1981, Marras et al., 1987, Lavender et al., 1989, Hodges and Richardson, 1996, Cholewicki et al.,
Spine stability
Until the late-1980’s, most attempts to understand the causes of work related low back injuries focused on loads exceeding some tissue tolerance level. However, this did not explain the large number of injuries that were occurring with loads that would not be considered hazardous. This paradox necessitated alternative explanations for occupational spine injuries. In fact, in the absence of muscles, buckling has been shown to occur with loads as low as 19 N on the osteoligamentous thoracolumbar
Future directions
This paper has presented a very brief overview of the progression of research in occupational spine biomechanics. While the many contributions of a vast number of researchers have had a positive impact on the health of workers, much work remains to be done. The following are some suggested areas needing further emphasis: (1) while most of the in vitro tissue testing studies, to date, have concentrated on compression loading, further research is needed to increase our understanding of tissue
Jim Potvin received a B.H.K. in Kinesiology from the University of Windsor (1986) and an M.Sc. (1988) and Ph.D. (1992) in Biomechanics from the University of Waterloo. He is currently an Associate Professor in the Department of Kinesiology at McMaster University. He researches and teaches primarily in the areas of biomechanics and the ergonomics of musculoskeletal injuries. His basic research focuses on the study of spine mechanics during load handling and the quantification of the effects of
References (94)
- et al.
Posture and the compressive strength of the lumbar spine
Clin Biomech
(1994) - et al.
A biomechanical model of the lumbosacral joint during lifting activities
J Biomech
(1985) - et al.
A biomechanical model calculation of muscle contraction forces: a double linear programming method
J Biomech
(1988) - et al.
Constraining spine stability levels in an optimization model leads to the prediction of trunk muscle co-activity and improved predictions of spine compression
J Biomech
(2005) - et al.
Exploring the geometric and mechanical characteristics of the spine musculature to provide rotational stiffness to two spine joints in the neutral posture
Hum Movement Sci
(2007) - et al.
The responses of leg and trunk muscles to sudden unloading of the hands: implications for balance and spine stability
Clin Biomech
(2003) Computerized biomechanical models–Development of and use in studying gross body actions
J Biomech
(1969)- et al.
Mechanical stability of the in vivo lumbar spine: implications for injury and chronic low back pain
Clin Biomech
(1996) - et al.
Euler stability of the human ligamentous lumbar spine: Part II experiment
Clin Biomech
(1992) - et al.
Repeated spinal flexion modulates the flexion–relaxation phenomenon
Clin Biomech
(2003)
Repetitive lifting tasks fatigue the back muscles and increase the bending moment acting on the lumbar spine
J Biomech
Function of erectores spinae in flexion of the trunk
Lancet
Response of trunk muscle coactivation in protecting against changes in spinal stability
J Biomech
Musculoskeletal load of push-pull tasks
Int J Ind Ergonom
The in vivo dynamic response of the human spine to flexion perturbations: Effects of pre-load and step input magnitude
Clin Biomech
The strength of the neural arch and the etiology of spondylolysis
Orthop Clin North Am
Effects of a simulated industrial bin on lifting and lowering mechanics
Int J Ind Ergonom
A comparison of peak vs cumulative physical work exposure risk factors for the reporting of low back pain in the automotive industry
Clin Biomech
Fatigue related responses of trunk muscles to a prolonged, isometric twist exertion
Clin Biomech
Ultimate strength of the lumbar spine in flexion: an in vitro study
J Biomech
An equation to calculate individual muscle contributions to joint stability
J Biomech
Reduction in anterior shear forces on the L4/L5 disc by the lumbar musculature
Clin Biomech
Flexion–relaxation response to static lumbar flexion in males and females
Clin Biomech
Stoop or squat: a review of biomechanical studies on lifting technique
Clin Biomech
Are recruitment patterns of the trunk musculature compatible with a synergy based on the maximization of endurance?
J Biomech
The relevance of torsion to the mechanical derangement of the lumbar spine
Spine
Effects of operator stance on pushing and pulling tasks
IEEE Trans
Stability of the lumbar spine: a study in mechanical engineering
Acta Orthop Scand Suppl
Fatigue fractures of human lumbar vertebrae
Clin Biomech
An evaluation of predictive methods for estimating cumulative spinal loading
Ergonomics
Motor responses in the human trunk due to load perturbations
Acta Physiol Scand
Prolonged activity of lumbar erectores spinae: an electromyographic and dynamometric study of the effect of training
Ann Phys Med
The in vivo dynamic response of the human spine to rapid lateral bend perturbations: Effects of pre-load and step input magnitude
Spine
Lumbar spine stability can be augmented with an abdominal belt and/or increased intra-abdominal pressure
Eur Spine J
Spondylolytic fractures
J Bone Joint Surg Br
Posture of the trunk during the lifting of weights
Brit Med J
Pressures in the trunk cavities when pulling, pushing and lifting
Ergonomics
The function of the erectores spinae muscles in certain movements and postures in man
J Physiol
Role of muscles in lumbar spine stability in maximum extension efforts
J Orthop Res
Prediction of metabolic rates for manual materials handling jobs
Am Ind Hyg Assoc J
Stoop or squat: a biomechanical and metabolic evaluation
IIE Trans
Spinal compression tolerance limits for the design of manual material handling operations in the workplace
Ergonomics
A combined finite element and optimization investigation of lumbar spine mechanics with and without muscles
Spine
Stability of dynamic trunk movement
Spine
Manual lifting and handling
Physiotherapy
Cited by (26)
Effects of load mass and position on the dynamic loading of the knees, shoulders and lumbar spine during lifting: a musculoskeletal modelling approach
2021, Applied ErgonomicsCitation Excerpt :For example, studies by Garg et al. (1982), McGill and Norman (1985) and de Looze et al. (1994) all showed that either the compressive forces or joint moments in the lumbar spine were significantly higher when employing 2-D dynamic models, even without the representation of trunk muscles. In 1986, McGill and Norman (1986) made a major advancement with the publication of a 3-D EMG-driven dynamic model with representations of 7 ligaments and 48 muscles (Potvin, 2008). Since then, several other detailed 3-D dynamic models have been published, e.g. by Granata and Marras (1995) and Kingma et al. (1996).
Relationship between leg and back strength with inter-joint coordination of females during lifting
2016, International Journal of Industrial ErgonomicsImage driven subject-specific finite element models of spinal biomechanics
2016, Journal of BiomechanicsCitation Excerpt :Establishing the loads present in the human spine and its associated tissues is of significant importance for understanding normal spinal function and problems such as degeneration (Adams, 2012), functional instability (Mulholland, 2008), manual handling injury (Potvin, 2008), and back pain (Yang et al., 2011) and for designing successful regenerative therapies and implants for degenerative disc disease (Weber et al., 2015).
Towards establishing an occupational threshold for cumulative shear force in the vertebral joint - An in vitro evaluation of a risk factor for spondylolytic fractures using porcine specimens
2013, Clinical BiomechanicsCitation Excerpt :To enhance spondylolytic injury models and lay the groundwork for additional threshold limit values that consider cumulative shear load exposure, it is appropriate to evaluate the influence that the magnitude of repetitively applied sub-maximal shear force has on fatigue of the vertebral joint, and in particular the PI. In response to a call put forward by Potvin (2008), quantifying the relationship between the magnitude of repetitively applied forces and the vertebral joint's shear fatigue life will provide a basis to establish appropriate cumulative threshold values. Controlled in vitro studies have the capability to isolate specific injury mechanisms and quantify tissue damage thresholds that can be used for assessments of injury risk.
Musculoskeletal disorder risk during automotive assembly: Current vs. seated
2012, Applied ErgonomicsCitation Excerpt :Skeletal muscle can generate large internal forces on the joints, tendons and nerve during movement that may lead to MSDs (Cutlip et al., 2009). Surface electromyography (EMG) and EMG-assisted spine loading models have been used to assess internal forces acting on the spine and the risk of low back disorders (Kim and Marras, 1987; Marras and Sommerich, 1991a; McGill and Norman, 1986; Garnder-Morse et al., 1995; Potvin, 2008). Furthermore, EMG of the shoulder muscles has also been used to assess exposure to physical demands in the workplace and subsequent risk of shoulder injury (Lee et al., 1997; Southard et al., 2007; Bao et al., 2009; Porter et al., 2010).
Jim Potvin received a B.H.K. in Kinesiology from the University of Windsor (1986) and an M.Sc. (1988) and Ph.D. (1992) in Biomechanics from the University of Waterloo. He is currently an Associate Professor in the Department of Kinesiology at McMaster University. He researches and teaches primarily in the areas of biomechanics and the ergonomics of musculoskeletal injuries. His basic research focuses on the study of spine mechanics during load handling and the quantification of the effects of muscle fatigue during repetitive or prolonged tasks. He also conducts applied research with a focus on developing valid ergonomic methods to quantify injury risk in the workplace; including the assessment of manual materials handling tasks and the evaluation of upper limb disorders.