Study Shows Back Injury Secondary To Muscle Fatigue

A recent study funded by the National Institute for Occupational Safety and Health shows the relationship between muscle fatigue from repetitive lifting and back injury. It was conducted by an Ohio State industrial systems engineer and an MD who is studying biomechanics. The study which recently appeared in Clinical Biomechanics is the first to examine muscle oxygenation throughout the workday.

The Study
Ten people participated in the study; six had at least one year’s experience in a job that requires lifting, such as in stocking shelves. Four were considered novice lifters. Each person wore a Lumbar Motion Detector, a device that was designed to measure the spine’s movement. They wore oximeters, a gauge that measures the oxygen level of the muscles – just like the pulse oximeter, a device that clips onto a finger, measures oxygen level of the blood.

Activity
Study participants lifted a box from a waist high stand and set it on a chest-high conveyor belt. The box traveled on a conveyor belt to the next participant, who would lift the box and set on another conveyor belt. The boxes weighed 2 pounds, 11 pounds, and 26 pounds. Participants worked 8 hours with a half-hour lunch break and two 15 minute breaks.

Researchers said that the 26 pound box weighed less than half as much as loads that some workers are routinely required to lift in industry. The researchers studied the oxygen levels in the muscles. After 2 hours of lifting, the oxygen level gradually increased until it reached 11% above the resting level. During hours 2 to 4, it rose to 13%. During the lunch break, the oxygen level returned to the resting level but immediately rose to 11 % with lifting during hours 4 to 6. During the last 2 hours of the work day, the oxygenation level rose to 16%, the highest level of the day. This oxygen level indicates how hard the muscles were working and whether they were becoming fatigued. Citing his study, Professor Marras of Ohio State, says, “ Because the oxygen demand at the end of the day was so much higher, that’s when we’d expect people to get hurt on the job.” As muscles fatigue and begin to hurt, workers tense up and try to lift with other muscles that are not as painful.

Conclusion
Tense muscles constrict blood vessels, preventing the flow of oxygen and nutrients to the tissues and the removal of waste produced by muscle activity. While using different muscles may bring relief at first, it increases stress on the joints and the spine, increasing the chance of injury. The muscles of inexperienced lifters tensed up more quickly as they needed more oxygen. Injuries were most likely to happen during the last 2 hours of a shift when muscles were the most fatigued.

Professor Marras showed in the study that half-hour breaks were more effective in reducing muscle fatigue but agreed that this might not be practical in the industry. The study also concluded that people who are new to lifting need to take breaks more often than experienced workers.
• According to the US Bureau of Labor Statistics, in 2002, there were more than 345,000 on the job back injuries which required time off from work.

• In 2004, a Harvard Medical School Study showed that back pain was the reason for over 100 million lost work days per year.

Perhaps this latest study on muscle fatigue could be helpful in implementing some changes in the workplace where back injury is a constant factor.

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Studies of Stress Related Back Pain

Life is full of stress and its physical effects can be felt throughout the body. Too much stress can lead to heart and blood pressure problems, ulcers and strokes, and the list goes on. You can hurt your back by lifting something but accumulated emotional stress and mental strain can also create pain and damage.

Sometimes back or neck pain is the body’s way of protecting itself and literally forcing a general slowdown. Stress creates tension in the muscles which leads to spasms that squeeze the blood vessels and reduce the flow of oxygen and nutrients to the tissues. Just as it brings nourishment to the tissues, the circulatory system also carries away the waste byproducts of muscle activity.

With increasingly tense muscles, there is a buildup of carbon dioxide and waste chemicals, such as lactic acid, in the tissues, leading to increased fatigue and pain. Stress also increases nerve activity in the muscles which increases tension and decreases flexibility. As the muscles lose their fuel supply, they weaken and are more susceptible to strain and injury.

The back is much less able to tolerate any abuse when under stress. Lifting a box incorrectly, making a sudden twist, poor posture, sitting too long in one position, can lead to back pain. Literally, your back can’t bear it, and that ‘pain in the neck’ or pain in the back’ becomes a protest against the stress.

A person who has a ‘bad back’ due to a degenerative disease or secondary to an old injury often notices the effects of stress more quickly than someone with a healthy back. If spinal nerves are all ready being compressed by the calcium deposits of arthritis or spinal stenosis, it may take just a small amount of stress with minimal muscle tension to further compress nerves, triggering pain.

Sciatica from a disc’s compression of the spinal cord or nerve roots may flare up when a person is feeling stressed and tense. The slightest muscle tension may become ‘the straw that broke the camel’s back’.

Studies Of The Relationship Between Stress And Back Pain

Swedish Army Recruits

Recently, a study of more than 48,000 men in the Swedish Army showed the link between back problems and the ability to cope with stress. A battery of medical examinations, intelligence tests, and assessment of their ability to cope with stress were carried out on these Swedish recruits. Researchers found that in this group:

• Over 5000 men had back problems severe enough to interfere with their military service. The vast majority of their disorders were ‘nonspecific back pain and disease’.
• The recruits who had poor coping skills were also most likely to have back pain.
• Those with good coping skills also had higher intelligence scores, which may indicate that the smarter you are, the better you have learned how to handle stress.

US Army Soldiers

In another study, 368 US Army soldiers who came to a clinic complaining of low back pain, completed a questionnaire about their work habits and their health.

• The study linked job stress to emotional stress and this was directly related to their clinic visit complaining of back pain. The greater the emotional distress felt by the soldier, the more visits that were required to relieve his back pain.
• This study confirmed research that linked psychological distress and the physiological demands of work to the increased risk of back pain symptoms.
• The Army researchers believe that job stress plays an important role in persistent low back pain and that reducing the stress can also reduce the pain.
  

Great Britain Study

A study in Great Britain of nearly 6000 people showed:

• If you are under psychological stress when in your 20s, you are more than twice as likely to suffer low back pain when you reach your thirties.
• Researchers believe that early stress may have an adverse effect upon muscle tone which will eventually lead to pain and injury in a vulnerable area.

Stress expert, Venetta Campbell, Ph.D. at Mount St. Mary’s College in Los Angeles, says, “”People who don’t learn how to cope effectively get sick”. She offers some basic stress fighting suggestions:

• Get regular exercise
• Eat a balanced diet
• Keep your finances in order
• Follow your own dreams and let go of external expectations
• Set goals – having a vision for your future helps reduce the stress of uncertainty. (Brought to you by Fort Lauderdale Chiropractor)