Study Examines Relationship Between Lifting and Low Back Pain
In manufacturing and other industries where lifting is part of the job, disorders that affect the muscles and bones are a common problem. In fact, musculoskeletal disorders cause one-third of work-related injuries resulting in missed workdays, costing about $45 to $54 billion annually in lost productivity and treatment, according to estimates from the National Research Council and the Institute of Medicine.
At the National Institute for Occupational Safety and Health (NIOSH), scientists study the causes and prevention of these prevalent disorders, including low back pain. Unlike some exposures, however, exposures related to low back pain may be more difficult to measure. In a study published in the journal Safety and Health at Work, NIOSH scientists adapted risk assessment methods typically used in chemical risk assessment to assess workers’ accounts and the revised NIOSH Lifting Equation to identify specific factors related to low back pain among a group of manufacturing workers. This equation calculates a composite lifting index, which is the ratio of the load lifted to the recommended weight limit for multiple lifting tasks performed consecutively.
The study participants included 138 manufacturing workers. Most were male, their average age was 38 years, and all reported that they were free of low back pain at the beginning of the study. Follow-up was 1 year. Statistical analysis showed that workers in this study who reported more lifts per work shift were more likely to report instances of low back pain than other workers.
Factors associated with fewer instances of self-reported low back pain in this study were non-work-related activities involving bending and twisting of the back, more overtime-work hours, and more years of overall employment. It is important to note that this study only identifies a relationship and does not prove that more lifts per work shift cause low back pain.
Similarly, it does not prove that bending and twisting of the back and the other factors examined were unrelated to low back pain. Further development of these risk assessment methods and research is necessary to confirm the study’s results and their possible application to identifying the causes of other work-related musculoskeletal disorders.
More information is available:
Non-chemical Risk Assessment for Lifting and Low Back Pain Based on Bayesian Threshold Models
NIOSH Ergonomics and Musculoskeletal Disorders
NIOSH Education and Information Division
Musculoskeletal Disorders (MSDs) are a common and costly problem for people and companies across the United States.
- MSDs are the single largest category of workplace injuries and are responsible for almost 30% of all worker’s compensation costs. (source: BLS)
- U.S. companies spent 50 billion dollars on direct costs of MSDs in 2011. (source: CDC)
- Indirect costs can be up to five times the direct costs of MSDs. (source: OSHA)
- The average MSD comes with a direct cost of almost $15,000. (source: BLS)
To lay the foundation for an MSD prevention strategy, it’s important to understand what MSDs are and what causes them. With this knowledge, you’ll be able to allocate your time, attention and resources most effectively to prevent MSDs.
Definition of Musculoskeletal DisorderSo what is a musculoskeletal disorder?
Musculoskeletal Disorders or MSDs are injuries and disorders that affect the human body’s movement or musculoskeletal system (i.e. muscles, tendons, ligaments, nerves, discs, blood vessels, etc.).
Common MSDs include:
- Carpal Tunnel Syndrome
- Muscle / Tendon strain
- Ligament Sprain
- Tension Neck Syndrome
- Thoracic Outlet Compression
- Rotator Cuff Tendonitis
- Radial Tunnel Syndrome
- Digital Neuritis
- Trigger Finger / Thumb
- DeQuervain’s Syndrome
- Mechanical Back Syndrome
- Degenerative Disc Disease
- Ruptured / Herniated Disc,
- and many more.
Other common names for MSDs are “repetitive motion injury”, “repetitive stress injury”, “overuse injury” and many more. The problem with using that kind of terminology is that it implicates a singular cause for damage to the musculoskeletal system – repetition and stress. This is limiting because more and more research is pointing to multiple causative risk factors leading to MSDs.
The Cause of Musculoskeletal Disorders – Exposure to Risk FactorsWhen a worker is exposed to MSD risk factors, they begin to fatigue. When fatigue outruns their body’s recovery system, they develop a musculoskeletal imbalance. Over time, as fatigue continues to outrun recovery and the musculoskeletal imbalance persists, a musculoskeletal disorder develops.
These risk factors can be broken up into two categories: work-related (ergonomic) risk factors and individual-related risk factors.
Work-related Risk FactorsWorkplace design plays a crucial role in the development of an MSD.
When a worker is asked to do work that is outside his body’s capabilities and limitations, he is being asked to put his musculoskeletal system at risk. In these situations, an objective evaluation of the workstation design tells us the worker’s recovery system will not be able to keep up with the fatigue that will be caused by performing the job. The evaluation will tell us that ergonomic risk factors are present, the worker is at risk of developing a musculoskeletal imbalance and a musculoskeletal disorder is an imminent reality.
There are three primary ergonomic risk factors.
- High task repetition. Many work tasks and cycles are repetitive in nature, and are frequently controlled by hourly or daily production targets and work processes. High task repetition, when combined with other risks factors such high force and/or awkward postures, can contribute to the formation of MSD. A job is considered highly repetitive if the cycle time is 30 seconds or less.
- Forceful exertions. Many work tasks require high force loads on the human body. Muscle effort increases in response to high force requirements, increasing associated fatigue which can lead to MSD.
- Repetitive or sustained awkward postures. Awkward postures place excessive force on joints and overload the muscles and tendons around the effected joint. Joints of the body are most efficient when they operate closest to the mid-range motion of the joint. Risk of MSD is increased when joints are worked outside of this mid-range repetitively or for sustained periods of time without adequate recovery time.
Evidence Base of Work-Related Risk Factors:
Musculoskeletal Disorders and Workplace Factors NIOSH / U.S. Department of Health & Human Services
The conclusion of this 590 page report is simple and straightforward:
“A substantial body of credible epidemiologic research provides strong evidence of an association between MSDs and certain work-related physical factors when there are high levels of exposure and especially in combination with exposure to more than one physical factor (e.g., repetitive lifting of heavy objects in extreme or awkward postures [Table 1]).Work-related Musculoskeletal Disorders: The Epidemiologic Evidence and the Debate Journal of Electromyography and Kinesiology
The strength of the associations reported in the various studies for specific risk factors after adjustments for other factors varies from modest to strong. The largest increases in risk are generally observed in studies with a wide range of exposure conditions and careful observation or measurement of exposures.”
“Thus there is an international near-consensus that musculoskeletal disorders are causally related to occupational ergonomic stressors, such as repetitive and stereotyped motions, forceful exertions, non-neutral postures, vibration, and combinations of these exposures.”Additional reading:
- Association of Occupational and Non-occupational Risk Factors with the Prevalence of Musculoskeletal Disorders
- Work-related Musculoskeletal Disorders (WMSDs): An Introduction
Individual-related Risk FactorsHuman beings are multi-dimensional. Limiting ourselves to a singular cause of MSDs will limit our ability to create a prevention strategy that addresses the multi-dimensional worker.
We need to address both workplace risk factors and individual risk factors.
Individual risk factors include:
- Poor work practices. Workers who use poor work practices, body mechanics and lifting techniques are introducing unnecessary risk factors that can contribute to MSDs. These poor practices create unnecessary stress on their bodies that increases fatigue and decreases their body’s ability to properly recover.
- Poor overall health habits. Workers who smoke, drink excessively, are obese, or exhibit numerous other poor health habits are putting themselves at risk for not only musculoskeletal disorders, but also for other chronic diseases that will shorten their life and health span.
- Poor rest and recovery. MSDs develop when fatigue outruns the workers recovery system, causing a musculoskeletal imbalance. Workers who do not get adequate rest and recovery put themselves at higher risk.
- Poor nutrition, fitness and hydration. For a country as developed as the United States, an alarming number of people are malnourished, dehydrated and at such a poor level of physical fitness that climbing one flight of stairs puts many people out of breath. Workers who do not take care of their bodies are putting themselves at a higher risk of developing musculoskeletal and chronic health problems.
Not convinced? Here is what the scientific literature has to say.
Evidence Base of Individual-related Risk Factors:
NIOSH Total Worker Health NIOSH
NIOSH supports a multi-dimensional view of workers, which they call “Total Worker Health”. This strategy integrates health protection with health promotion because they recognize that, “emerging evidence recognizes that both work-related factors and health factors beyond the workplace jointly contribute to many health and safety problems that confront today’s workers and their families.”
“Total Worker Health is a strategy integrating occupational safety and health protection with health promotion to prevent worker injury and illness and to advance health and well-being.”
Here is a quote from the NIOSH Total Worker Health Seminal Research Papers (2012):
“Today, emerging evidence recognizes that both work-related factors and health factors beyond the workplace jointly contribute to many health and safety problems that confront today’s workers and their families. Traditionally, workplace health and safety programs have been compartmentalized. Health protection programs have focused squarely on safety, reducing worker exposures to risk factors arising in the work environment itself. And most workplace health promotion programs have focused exclusively on lifestyle factors off-the-job that place workers at risk. A growing body of science supports the effectiveness of combining these efforts through workplace interventions that integrate health protection and health promotion programs.”Work-related Musculoskeletal Disorders: Prevention report European Agency for Safety and Health at Work
“Epidemiological studies have shown that some personal risk factors for MSDs such as smoking, being overweight, or in poor physical shape are the same factors as those relating to poor general health. Therefore general health promotion at the workplace might be one option to prevent MSDs.”Work-related Musculoskeletal Disorders Assessment and Prevention InTech
“Practice shows that the collaboration of people with expertise in different areas (e.g. engineering, psychology, human relations) is advantageous as this allows MSD-related issues to be approached in a global way. However, the involvement and participation of all employees and their representatives is crucial to success in such a holistic approach and, moreover, in creating a culture where ergonomics and the prevention of musculoskeletal disorders is embedded in every part of the process.”
“The recognition of personal risk factors can be useful in providing training, administrative controls, and awareness. Personal or individual risk factors can impact the likelihood for occurrence of a WMSD (McCauley-Bell & Badiru, 1996a; McCauley-Bell & Badiru, 1996b). These factors vary depending on the study but may include age, gender, smoking, physical activity, strength, anthropometry and previous WMSD, and degenerative joint diseases (McCauley Bush, 2011).” …Work-related Musculoskeletal Disorders: The Epidemiologic Evidence and the Debate Journal of Electromyography and Kinesiology
Besides risk factors related to work other risk factors contribute to its development, namely factors intrinsic to the worker and factors unrelated to work. A risk factor is any source or situation with the potential to cause injury or lead to the development of a disease. The variety and complexity of the factors that contribute to the appearance of these disorders explains the difficulties often encountered, to determine the best suited ergonomic intervention to be accomplished in a given workplace, to control them. Moreover, despite all the available knowledge some uncertainty remains about the level of exposure to risk factors that triggers WMSD. In addition there is significant variability of individual response to the risk factors exposure. The literature review and epidemiological studies have shown that in the genesis of the WMSD three sets of risk factors can be considered (Bernard, 1997; Buckle & Devereux, 1999; Nunes, 2009a): Physical factors – e.g., sustained or awkward postures, repetition of the same movements, forceful exertions, hand-arm vibration, all-body vibration, mechanical compression, and cold; Psychosocial factors – e.g., work pace, autonomy, monotony, work/rest cycle, task demands, social support from colleagues and management and job uncertainty; Individual factors – e.g., age, gender, professional activities, sport activities, domestic activities, recreational activities, alcohol/tobacco consumption and, previous WMSD.”
“As with most chronic diseases, MSDs have multiple risk factors, both occupational and non-occupational. In addition to work demands, other aspects of daily life, such as sports and housework, may present physical stresses to the musculoskeletal tissues. The musculoskeletal and peripheral nerve tissues are aﬀected by systemic diseases such as rheumatoid arthritis, gout, lupus, and diabetes. Risk varies by age, gender, socioeconomic status, and ethnicity. Other suspected risk factors include obesity, smoking, muscle strength and other aspects of work capacity.”
Identify ProblemsAn important part of the ergonomic process is a periodic review of the facility, specific workstation designs and work practices, and the overall production process, from an ergonomics perspective. This includes identifying existing problems, which can be obtained from reviewing the company's OSHA 300 injury and illness logs, 301 reports, workers' compensation records, and worker reports of problems. However, a more forward-looking approach, to be used in combination with reviewing injury and illness records, is to be proactive in identifying potential ergonomic issues that have gone unnoticed or resulted from facility changes, before they result in MSDs. Observations of workplace conditions and work processes, ergonomic job analyses, workplace surveys, and worker interviews are common proactive methods for identifying ergonomics related injury risks.
- Review Injury Records
- Observe Workplace Conditions
- Encourage Early Reporting of Injuries
Review Injury RecordsLooking at your injury and illness data will help identify ergonomic problems. These data can be obtained from reviewing the company's OSHA 300 Injury and Illness Logs, 301 reports, workers' compensation records, first aid logs, accident and near-miss investigation reports, insurance company reports and worker reports of problems.
Observe Workplace ConditionsBy looking critically at your workplace operations, you can identify risk factors and eliminate or control them as early as possible.
Risk FactorsThe risk of MSD injury depends on work positions and postures, how often the task is performed, the level of required effort and how long the task lasts. Risk factors that may lead to the development of MSDs include:
- Exerting excessive force. Examples include lifting heavy objects or people, pushing or pulling heavy loads, manually pouring materials, or maintaining control of equipment or tools.
- Performing the same or similar tasks repetitively. Performing the same motion or series of motions continually or frequently for an extended period of time.
- Working in awkward postures or being in the same posture for long periods of time. Using positions that place stress on the body, such as prolonged or repetitive reaching above shoulder height, kneeling, squatting, leaning over a counter, using a knife with wrists bent, or twisting the torso while lifting.
- Localized pressure into the body part. Pressing the body or part of the body (such as the hand) against hard or sharp edges, or using the hand as a hammer.
- Cold temperatures. In combination with any one of the above risk factors may also increase the potential for MSDs to develop. For example, many of the operations in meatpacking and poultry processing occur with a chilled product or in a cold environment.
- Vibration. Both whole body and hand-arm, can cause a number of health effects. Hand-arm vibration can damage small capillaries that supply nutrients and can make hand tools more difficult to control. Hand-arm vibration may cause a worker to lose feeling in the hands and arms resulting in increased force exertion to control hand-powered tools (e.g. hammer drills, portable grinders, chainsaws) in much the same way gloves limit feeling in the hands. The effects of vibration can damage the body and greatly increase the force which must be exerted for a task.
- Combined exposure to several risk factors. May place workers at a higher risk for MSDs than does exposure to any one risk factor.
- Modifying their tools, equipment or work area
- Shaking their arms and hands
- Rolling their shoulders
- Bringing products such as back belts or wrist braces into the workplace
Once problem jobs are identified, conducting an in-depth ergonomic job analysis can help identify solutions to prevent MSDs. An ergonomic job hazard analysis is a technique that focuses on job tasks as a way to identify hazards before they occur. It focuses on the relationship between the worker, the task, the tools, and the work environment.
Encouraging and Utilizing Early Reports of InjuryComprehensive injury reporting is important to the success of an ergonomic process. The goal of this effort is to properly assess, diagnose, and treat MSDs. Early reporting, diagnosis, and intervention can limit injury severity, improve the effectiveness of treatment, minimize the likelihood of disability or permanent damage, and reduce workers compensation claims. This will allow the employer to correctly identify work areas or specific tasks where injuries frequently occur or are most severe. This information helps direct the activities of the ergonomic team as well as to guide healthcare providers in making return-to-work and light-duty work decisions. OSHA's injury and illness recording and reporting regulation (29 CFR Part 1904) require employers to record and report work-related fatalities, injuries and illnesses.
- Frequently Asked Questions for OSHA's Injury and Illness Recordkeeping Rule. OSHA. Additional guidance to help employers comply with the recordkeeping requirements. The following table of contents provides links to additional guidance, or, if additional guidance has not been developed, to the regulation.
- Reinforces worker training on recognizing MSD symptoms.
- Encourages early reporting of MSD symptoms.
- Allows for prompt medical evaluations for diagnosis, treatment and follow-up care.
- Reduces injury severity, the number of workers' compensation claims and associated costs and the likelihood of permanent disability.
- Provides guidance on return-to-work and work placement restrictions during the healing process.
- Guides job modifications.
- Provides a mechanism to track and trend MSD injuries.
- Enables assessment of the effectiveness of work changes.
Resources on Risk Factors
- Easy Ergonomics: A Practical Approach for Improving the Workplace. California Department of Industrial Relations (Cal/OSHA), (1999). Section II, Ergonomics and Your Workplace, page 7. Provides descriptions and examples of common factors that contribute to the development of MSDs.
- Fitting the Task to the Person: Ergonomics for Very Small Businesses. California Department of Industrial Relations (Cal/OSHA), (2000). Provides descriptions and examples of common risk factors with solutions.
- Work Related Musculoskeletal Disorders (WMSDs). Canadian Centre for Occupational Health and Safety. (December 12, 2005). Outlines common risk factors and their injuries.
- Musculoskeletal Disorders and Workplace Factors. U.S. Department of Health and Human Services (DHHS), National Institute for Occupational Safety and Health (NIOSH) Publication No. 97-141. (July 1997). Reviews the majority of the relevant studies available at the time and documents the relationship between MSDs and various workplace factors.
- National Research Council. Musculoskeletal Disorders and the Workplace: Low Back and Upper Extremities. Washington, DC: The National Academies Press, 2001. Presents the latest information on the prevalence, incidence and costs of musculoskeletal disorders and identifies factors that influence injury reporting.
- National Research Council. Work-Related Musculoskeletal Disorders: A Review of the Evidence. Washington, DC: The National Academies Press, 1998. Based on evidence presented and discussed at the two-day Workshop on Work-Related Musculoskeletal Injuries: Examining the Research Base and on follow-up deliberations of the steering committee assembled by the National Academy of Sciences/National Research Council.
- National Research Council. Work-Related Musculoskeletal Disorders: Report, Workshop Summary, and Workshop Papers. Washington, DC: The National Academies Press, 1999.Includes a steering committee report, workshop information and a review of interventions.
Resources on Job Analysis
- Job Hazard Analysis. OSHA Publication 3071, (Revised 2002). Explains what a job hazard analysis is and offers guidelines to help conduct your own step-by-step analysis.
- Easy Ergonomics: A Practical Approach for Improving the Workplace. California Department of Industrial Relations (Cal/OSHA), (1999). Ergonomics Job Analysis Methods, and Ergonomic Awareness Checklist, pages 19-25.
- Ergonomic Assessment Toolkit. American Industrial Hygiene Association (AIHA) Ergonomic Committee, (2011). Provides a consolidated resource of commonly used ergonomic assessment tools with explanation of when, where and how each tool is applied. An electronic link is provided for each tool.
- Assessment Tools. Department of Defense (DoD) Environment, Safety and Occupational Health Network and Information Exchange (DENIX), Ergonomics Working Group. Provides links to assessment tools and prevention strategies developed by the DOD Ergonomics Working Group.
- Manual handling. Health and Safety Executive (HSE). Contains tools to help employers analyze lifting and moving (MAC tool), repetitive tasks like twisting, bending and repeated movements (ART tool) and push/pull.
- Analysis Methods and Tools for Ergonomists. Thomas E. Bernard, University of Southern Florida, College of Public Health. Provides a suite of advanced tools, which may require outside training or direction or use by an experienced practitioner.
- Liberty Mutual Manual Materials Handling Tables. Liberty Mutual Research Institute for Safety, (2012). These tables present information about the percentages of men and women capable of performing manual material handling tasks without overexertion.
- Evaluation Tools. Washington State Department of Labor and Industries. Provides links for evaluation tools.
- Applications Manual for the Revised NIOSH Lifting Equation. U.S. Department of Health and Human Services (DHHS), National Institute for Occupational Safety and Health (NIOSH) Publication No. 94-110. (January 1994). Contains a complete description of all terms in NIOSH's lifting equation with several sample calculations.
- Health Hazard Evaluations.
National Institute for Occupational Safety and Health (NIOSH). NIOSH
conducts investigations of possible health hazards in the workplace.
This page allows a search for all NIOSH evaluations concerning
- Ergonomic Evaluation of Surfacing and Finishing Tasks during Eyeglass Manufacturing - Minnesota. HETA 2010-0114-3168. (November 2012). An evaluation of potential ergonomic risk factors in eyeglass manufacturing.
- Ergonomic Evaluation of Automatic Flat Sorting Machines - Colorado. HETA 2008-0293-3132. (June 2011). An Evaluation of potential ergonomic hazards among workers using the AFSM 100 machines.
- Ergonomic Evaluation at a Steel Grating Manufacturing Plant. HETA 2008-0074-3081. (May 2009). An investigation on the high number of MSDs in employees working in the barline, welding, and saw areas.
- Ergonomic Evaluation of Workers at a Cabinet Mill and Assembly Plant. HETA 2007-0038-3057. (March 2008). An evaluation of potential ergonomic hazards among cabinet makers.
- Interpreters for the Deaf. HETA 92-0268-2477. (December 1994). An evaluation of the problem of MSDs among interpreters for the deaf.
Resources on Injury Rates
- Worker Health eChartbook: Musculoskeletal Conditions - Magnitude and Trend. Centers for Disease Control and Prevention (CDC). Provides descriptive occupational morbidity and mortality data in the United States. It includes figures and tables describing the magnitude, distribution and trends of the nation's occupational injuries, illnesses and fatalities.
- Nonfatal Occupational Injuries and Illnesses Requiring Days Away from Work. U.S. Department of Labor, Bureau of Labor Statistics (BLS) Economic News Release. Contains summary and MDS statistics (incidence rates by industry), including data tables of nonfatal occupational injuries and illnesses that require days away from work in private industry, state government, and local government.