Stuart McGill, Ph.D., spinal biomechanist at the University of Waterloo, Canada, states, "Industrial low back injury is an extremely complex issue and will only be successfully addressed by those willing to combine the wisdom of several different approaches and to form an integrative approach that is scientifically justifiable" (2).
Back pain is pervasive in our society, with 60% to 80% of the population suffering from some kind of back injury or back pain (1). Back pain is the most frequent cause of activity limitation among those under age 45 (3). However, the peak age for back injury is 40 (1). It is estimated that 80% to 90% of those with back pain will recover within 3 to 6 days, regardless of treatment (1). Thirty million dollars is spent on visits to private physicians (4), but only 3% of the total cost goes to prevention (1).
Intervertebral Discs and Back Pain
Drs. Andersson, Fine, and Silverstein (1) indicate that only 1% to 5% of back pain is related to an injury to the intervertebral disc. This information is based upon the fact that intervertebral disc degeneration is common in old age and can be found in people without back pain (1). Moreover, many autopsy specimens show the onset of intervertebral disc degeneration by the third decade of life (1). Drs. Andersson, Fine, and Silverstein (1) state, "It is important to recognize that the presence of a narrowed intervertebral disc (on X-ray) is not correlated with the risk for, or the presence of, a disc herniation, and it does not provide an explanation of the patient's pain in most cases." X-rays of the spine are commonly used to diagnosis the cause of back pain. However, the diagnostic value of X-rays do not justify the radiation exposure or cost (1). Arguably, the best clinical diagnostic tool is the straight leg-raising test, which will elicit pain when there is the presence of positive nerve root tension (1).
As intervertebral disc injuries relate to an occupational setting, Dr. Videman and colleagues (4) documented the increased risk of disc herniation for those who perform sedentary jobs characterized by sitting. Some of the mechanical changes of the disc, associated with sitting, include increased intra-discal pressure compared with standing and increases in posterior disc strain. These pressure changes are caused by the spine not being aligned like it is when a person is standing with good posture. Recent occupational recommendations proposed a 50-minute sitting limit (2). In physically demanding jobs, repetitive movements (most commonly trunk flexion followed by extension to neutral) of the spine result in micro-traumas to the disc(s) that can lead to a macro-trauma, which would cause a herniated disc (2).
Most Common Cause of Back Injury
Strains to the muscle and tendon appear to be the most common cause of low back pain (2). Drs. Andersson, Fine, and Silverstein (1) indicate that 95% to 99% of all back pain involves injury to the muscles and tendons. Dr. McGill (2) indicates that torn ligaments during lifting or other normal activities are more uncommon than common. Most back injuries are caused by micro-traumas from sub-failure magnitude loads that eventually lead to a macro-trauma or a severe strain (2). A strain can be classified as muscle disruption caused by indirect trauma (excessive stretch or tension). Injury occurs when the applied load exceeds the failure tolerance, or strength, of the tissue (2).
In an occupational, exercise, or recreational setting, or even during household or gardening work, a person can perform movements that cause micro-traumas to the tissues. These movements causing the micro-trauma(s) can be performed for weeks, months, or years until a movement causes failure of the tissue, resulting in a macro-trauma. As such, most back injuries do not just happen. Dr. McGill (2) states, "Loads on individual tissues can be surprisingly high, in fact, given the magnitude of tissue loads during performance of quite ordinary daily tasks, our enjoyment of lengthy periods free from injury fosters an appreciation for the magnificent strength and durability of the low back."
Common movements, or postures, that can cause micro-traumas include repeated unbalance or incorrect lifting, prolonged static postures of the spine such as trunk flexion without reversal of the posture, chronic physical stress on spine and muscles, or chronic sitting with little movement.
Research on back pain has found several factors that can contribute to injury. The investigations have identified individual and occupational risk factors. Moreover, within the occupational risk factors, physical and psychologic factors have been found to contribute to back injuries.
Individual Risk Factors
Dr. Bigos and colleagues (5) found that psychological factors were more important than physical factors as risk indicators for claims for low back injuries. Other risk factors that have been found in the research include lack of sleep or fatigue, emotional instability, substance abuse (alcohol or drugs), smoking (5), family problems, excessive body weight, physical inactivity, physical activity (excessive movement or incorrect movement), poor muscle endurance, and previous back injury.
Occupational Risk Factors
Physical factors in the work setting that put a worker at risk for a back injury include continuous heavy physical work, prolonged sitting, chronic "high risk" postures when standing (many workers are forced into chronic trunk flexion because their work station is too low), repetitive bending, twisting, pushing, pulling, lifting, slipping, tripping or falling, vibration during continuous driving, poor muscle endurance (this is especially true for people whose jobs require lifting and carrying), twisting a "loaded" spine (a spine is considered "loaded" when a worker manually picks up, carries, or puts down a load), and not using mechanical lifting devices.
The risk factors for back injury that are psychological in nature include a job that has high chronic stress (chronic stress releases hormones such as cortisol that have been implicated in muscle and tendon injury), low work satisfaction, low motivation or boredom, and mental fatigue, which may cause a worker to "forget" to lift properly.
"The Boeing Study" of Low Back Pain
This study (5) was conducted at the Boeing plant in Everett, WA. The investigators used 3,020 volunteers to study the incidence of, and risk factors for, lower back pain. Approximately 60% to 65% of the risk factors for back pain were "non-physical." Range of motion and isometric lifting strength were not helpful in predicting back injuries. Physical capacities and demographics had no significance. Smoking had a 40% increased risk for back injury, while previous back injury had a 60% increased risk. The authors conclude that back pain is a multifaceted problem. Physical factors are important, but other factors such as psychological stress provide strong predictive information. Many times, back problems seem to be only a part of the problem, rather than the patient's total problem.
Can Back Injuries Be Prevented?
What impact can exercise professionals have on preventing back injuries? Exercise professionals can give information about the cause of back injury, risk factors, and prevention. Exercise professionals also have knowledge about the positive effects of exercise on back injury prevention.
Prevention of back injury needs to focus upon exercise both in and out of the workplace. Exercise out of the workplace includes regular exercise to reduce the adverse effects of stress. A focus on regular exercise to improve body awareness, self-esteem, and psychological factors is important (5). Exercise to improve muscle endurance, primarily the endurance of the muscles supporting the spine, is important (2). Muscle endurance is the key component of fitness for industrial workers because they perform their work over long periods of time each day. As Dr. McGill (6) states, "It appears that the safest and mechanically most justifiable approach to enhancing lumbar stability through exercise entails a philosophical approach consistent with endurance, not strength; that ensures a neutral spine posture when under load (or more specifically avoids end range of motion positions) and that encourages abdominal cocontraction and bracing in a functional way." Dr. McGill (7) further indicates the spine is like a fishing rod. If a fishing rod were placed upright on the ground and a load were placed on top, it would bend and would not be able to support the weight. But if guy wires were attached at different levels to the fishing rod and anchored to the ground, the rod then would be able to withstand a load from the top without buckling. This same concept holds true with the spine. The stronger the muscles that support the spine are (rectus abdominus, internal and external obliques, transverse abdominus, and erector spinea group), the more stable the spine will be and, theoretically, less susceptible to injury. Increasing the stiffness of the muscles increases stability and increases ability to support larger loads.
With reference to nonwork exercise to help prevent back injury, there are three areas of importance: 1) aerobic exercise, 2) weight training, and 3) specific exercises to make the spine-stabilizing muscles stronger. Aerobic exercise and weight training help decrease the adverse physical and psychological effects of stress. They improve general conditioning and over-all health. They can have a dramatic effect on reducing fat percentage and body weight. As exercise relates to the intervertebral disc, movement associated with exercise can enhance circulation to the intervertebral discs because they are without a good blood supply. Regular exercise can have a positive effect on body awareness and self-esteem. Exercise may help with smoking cessation. And there is some evidence that regular exercise can improve sleep health.
Spine stabilization exercises are multifaceted and include functional range of motion exercises and endurance exercises for the muscles of the trunk. Range of motion exercises as opposed to trying to increase the flexibility of the back muscles are more beneficial. Evidence suggests that people with greater ranges of spine motion have increased risk for back injury (5). The back needs stability, not mobility (6, 7). The "cat-camel" (6, 7) exercise is good for functional range of motion (can be performed while on "all-fours" on the floor) (Figures 1 and 2).
Enhanced muscle endurance with neutral spine (maintaining natural curves in the spine) exercises and cocontraction of the muscles that brace the antagonistic muscles are important (6, 7). Dr. McGill (6) indicates that sit-ups (straight and bent knee) or leg raises have compressive loads exceeding National Institute for Occupational Safety and Health (NIOSH) guidelines and are not recommended. Curl-ups activate the rectus abdominis but not a lot of the obliques. Curl-ups with a twist can put unusually high compressive loads on the lumbar intervertebral discs (6). There is no single abdominal exercise that challenges all abdominal musculature. Most traditional back extensor exercises have very high intervertebral disc compressive and shear loads (6). Dr. McGill (6, 7) recommends the following exercises: curl-ups (with one knee flexed) or modified front-bridge or front-bridge for the rectus abdominis (see Figures 3, 4, and 5); modified side-bridge or side-bridge for the obliques and quadratus lumborum (see Figures 6 and 7); and modified bird-dog or bird-dog for back extensors (see Figures 8, 9, 10, and 11).
Workplace Exercises for Back Injury Prevention
Exercises in the workplace can include pre-work warm-up routines (PWWP) and workstation stretching/range or motion exercises (WSS). Dolan and colleagues (8) postulate that there is an increased risk of injury to the intervertebral discs early in the morning because of fully hydrated discs. Warm-up exercises before work may help "pump" fluid out of the discs. Dr. Moore (9) conducted a study to investigate the effects of participation in a stretching program on preventing muscle strains in the work place. There were 60 employees who performed 36 sessions of stretching. Measurements of flexibility on three tests improved, and there were no musculoskeletal injuries in the 2-month program. In addition, body perception, body attractiveness, and over-all self worth improved. Dr. Hilyer and colleagues (10) used 469 municipal firefighters to examine the effect of workplace stretching on incidence and severity of joint injuries. The authors state, "Although incidence of injury was not significantly different from the experimental and control groups, injuries sustained by the experimental group resulted in less lost time costs. Findings indicate that the flexibility training group program had a beneficial effect on reducing the severity and costs of joint injuries in the firefighting population."
Many companies give anecdotal evidence of the benefits of PWWP routines for their employees. Some benefits include lower workers' compensation insurance claims (workers' compensation insurance claims costs were 83% lower 1 year after the implementation of a PWWP) and a healthier and more versatile workforce; in addition, PWWP caused several people to schedule fitness assessments to join the on-site fitness center. Michael R. Bracko, Ed.D.,CSCS, FACSM, (11) reports the following benefits from an 8-year voluntary PWWP program at an industrial machine shop: only 14% of all injuries occurred to participants of the PWWP, no back injuries occurred to PWWP participants, and PWWP participants reported they felt ready to work, were more aware of their bodies, felt less likely to suffer a back injury, and felt a sense of satisfaction by doing something good for themselves.
Specific back exercises in a PWWP include repetitions of lateral trunk flexion, repetitions of scapular adduction, static contraction of the scapular adductors, hip circles, circumduction of sacrum, standing McKenzie exercises (standing back extension, see Figures 12 and 13), "cat-camel" with hands on bent knees (see Figures 1 and 2), isometric bracing of the abdominal muscles, and a total body movement by reaching up as high as possible on toes then bending the knees and torso to touch toes.
Workstation stretching and movements include standing up and producing any movement after prolonged sitting (it is sound practice to design into sedentary sitting jobs upright dynamic movement every 50 minutes), standing McKenzie exercises, standing "cat-camel," repetitions of lateral trunk flexion, static contraction of the scapular adductors to stretch the scapular abductors, hip circles, and circumduction of the sacrum. Workstation exercises typically last 30 seconds to 1 minute. Workstation exercises must be able to be performed in the confines of a small workstation. The people performing the exercise must feel comfortable performing the exercises.
Back pain and injury is a multifaceted problem. To successfully address this complex issue, exercise professionals must consider several different approaches that are scientifically justifiable for education and prevention. Back pain is pervasive in our society. Approximately 60% to 80% of the population will suffer from some kind of back pain. Millions of dollars are spent on doctors visits for back pain, but very little money is spent on prevention programs.
Only 1% to 5% of back pain is related to the disc. The presence of a narrowed intervertebral disc on an X-ray is not indicative of a herniated disc. A positive straight leg-raising test is commonly used to diagnosis a herniated disc. X-rays are a poor diagnostic tool for back pain.
Back strains, involving the muscles and tendons, are the most common causes of occupational low back pain. Injuries typically result from micro-traumas over weeks, months, and years, which lead to a macro-trauma and disability. Common movements, or postures, causing micro-traumas include repeated incorrect lifting, repeated static postures, chronic physical stress on the spine, or chronic sitting with little movement.
There are individual and occupational risk factors for back pain and injury. Occupational risk factors are divided into physical and psychological. The psychological risk factors have been found to be more significant in predicting back injuries than the physical risk factors (6). The "Boeing Study" (6) found "non-physical" factors to be the best predictors of back pain.
Exercise to prevent back injuries can be performed in and out of the workplace. Exercise out of the workplace focuses upon reducing the adverse effects of stress. Aerobic exercise and weight training are important for the multitude of benefits received from these types of exercise. Specific exercises to improve the endurance of the torso muscles that support the spine are important. When performing these exercises, they should be done with a neutral spine to limit the compressive loads on the intervertebral discs. Workplace exercises include PWWP and WSS routines. Prework warm-up exercises function to warm up the back and get it ready to work. Workstation stretching and exercise routines are designed to increase blood flow to the back and intervertebral discs and to increase movement.
Condensed Version and Bottom Line
According to the statistics, most people will suffer from back pain at least once in their lives. While a tremendous amount of money is spent on treating people with back pain, little money is spent on prevention. Muscle and tendon strains are the most common cause of back injury, and mental stress is a risk factor both in and out of the workplace. One of the most important aspects of prevention is to reduce the negative effects of mental stress. Thebest way to do that is to exercise and practice stress management techniques. A regular exercise program that includes specific abdominal, side and lateral, and back muscle endurance exercices is important for prevention. In the workplace it appears that a pre-work warm-up and workstation stretching can have some preventative effects on back injuries.
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10. Hilyer, J.C., K.C. Brown, A.T. Sirles, et al. A flexibility intervention to reduce the incidence & severity of joint injuries among municipal firefighters. Journal of Occupational Medicine
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Keywords:© 2004 American College of Sports Medicine
Back Injuries; Risk Factors; Injury; Occupational Performance