Lumbar Back Belts in the Workplace
There are few topics in occupational medicine that can stimulate more controversy and debate than the utility of lumbar belt use in the workplace. Over the years researchers have attempted to study the putative benefits of these lumbar supports since affirmatory evidence of positive results could have far reaching implications in employer policy making. Back injuries have been the leading cause of disability in the United States for people younger than 45 years of age, and have been the most expensive health care problem for the 30-50 year old age group.1
In Canada, back injuries account for over 25% of all lost time claims, the largest single claims category in most workers compensation jurisdictions.2 A similar prevalence is seen in the US with back injuries accounting for approximately 23% of all workers compensation payments ($13 billion) in 2002. The Bureau of Labor Statistics indicates that in 1998 there were 279,507 back injuries caused by overexertion that resulted in lost work days, 89% being in materials handling type jobs.1 In response to the enormous social and economic losses involved with back injury, many employers have attempted to adopt preventive measures, specifically, the widespread use of industrial back belts.3
How clinicians, researchers and policymakers feel about back supports have partly to do with their individual perspective on the nature of back pain and how it interacts with a particular employees work setting, job satisfaction level (psycho-social factors) and underlying conditioning level. Over the years, several postulated mechanisms of action for back belts have been popularized, most of these relating to a belt’s ability to affect a positive biomechanical alteration in the worker. This report will examine the research support for these common beliefs along with some of the epidemiological data that examines the effectiveness of these back supports in industry to date.
Do Belts Increase Intra-abdominal Pressure?
There have been numerous mechanisms of action for back belts that have been studied and made popular over the years. Barron and Feuerstein list 5 mechanisms which have been studied and debated including; a back belt’s ability to redistribute spinal forces during a lift action so that there is an increased intra-abdominal pressure (IAP).4 The potential effect of increasing IAP resulting in a decreased intradiscal pressure (IDP) has been studied and supported by some investigators, while challenged by others. Two studies suggested that by wearing a back belt, a person could reduce their risk of injury. Both studies (Harmon et al 1989 and Lander et al 1992) reported ground reaction forces and measured intra-abdominal pressures while subjects repeatedly lifted a weight. Both reports identified an increase in IAP in persons wearing the belt. These research groups made the assumption that IAP is a good indicator of spinal forces, and that an increase in IAP is indicative of increased low back support thereby justifying the use of a back belt.5-6 The underlying rationale for their conclusions however had been tested by other groups in the past, and remained contentious at best. McGill and Norman had questioned the hypothesized link between elevated IAP and a reduction in low back load. In 1987 they used an analytical model and data collected on several subjects lifting varying load magnitudes. They found that an increase in IAP required additional activation of abdominal musculature with a resultant increase in spinal compressive load.7 This was consistent with some work done the year before by Nachemson et al where they found that performing a Valsalva maneuver increased, not decreased, the spinal disc compression loads. In this study, four subjects without a history of back pain were tested during three sitting and two standing conditions, with and without using a Valsalva maneuver. These were isometric tasks while intradiscal (IDP).
IAP and Lumbar Muscle Activity
Another prevailing hypothesis regarding wearing a lumbar support while lifting is that the belt provides an increase in IAP and this leads to a reduced low back extensor muscle activation or strain level. A study by McGill et al investigated the effect of breathing on IAP and IDP, in the belted and unbelted condition, with and without a Valsalva maneuver. They used six males without low back pain as test subjects. When using the Valsalva maneuver during lifting, they observed peak IAPs being elevated, as opposed to peak IAPs during lifting without Valsalva maneuver. As well, EMG activity of the erector spinae muscles was decreased when lifting and using the Valsalva maneuver, as compared with EMG activity during lifting without the Valsalva maneuver. This finding may indicate that decreases in erector spinae muscle activity result primarily from the use of a Valsalva maneuver, and are not related to belted or unbelted conditions.8 The wearing of a belt was found to increase IAP by approximately 20%, so the authors further hypothesized that if belts indeed supported some of the low back extensor moment, they should expect to measure a reduction in extensor muscle activity. EMG readings showed no change in muscle activity for the back extensors or abdominal muscles.9 Lander et al examined lumbar muscle EMG activity in six male subjects without low back pain. They used two belted conditions and no belt condition. During lifting at 70% repetition maximum, they noted a reduction in erector spinae EMG activity in both belted conditions as compared to the no belt condition.10 In a separate study conducted two years later, Lander et al found that there were no reductions in lumbar muscle EMG activity in either belted or unbelted conditions.7
“There is mounting evidence that wearing a lumbar support can cause an increase in blood pressure...Both heart rate and blood pressure were increased by as much as 15 mmHg in subjects wearing belts.”
Ciriello and Snook examined 13 men over a four week period lifting several metric tons in four hours, twice a week — both with and without a belt. No differences in EMG median frequency signal in lumbar muscles were found between belted and non belted conditions. The findings did not support the idea that wearing a lumbar belt will significantly alleviate back extensor muscle loading.11 Woodhouse et al investigated the effects of two types of lumbar supports on lifting capability of nine male athletes without low back pain. The subjects performed isokinetic squat lifts at three different speeds in both belted and unbelted conditions. No differences were measured in maximum lift capacity by any of the three groups further strengthening the notion that wearing a lumbar belt may not impart any muscle unloading advantage.12