Academic journal article Human Factors

Effect of Lifting Belts on Trunk Muscle Activation during a Suddenly Applied Load

Academic journal article Human Factors

Effect of Lifting Belts on Trunk Muscle Activation during a Suddenly Applied Load

Article excerpt

The National Institute for Occupational Safety and Health suggests there is insufficient biomechanical or epidemiological evidence to recommend the use of back belts in industry. From a biomechanical perspective, previous work suggests that lifting belts stiffen the torso, particularly in the frontal and transverse planes. To determine whether lifting belts stiffen the torso and alter the trunk muscle response during a sudden loading event, we tested the hypotheses that (a) lifting belts alter peak muscle activity recorded with electromyography (EMG) during sudden loading and (b) lifting belts have a larger impact on trunk muscle response when sudden loads are applied asymmetric to the torso's midsagittal plane. A sudden load was delivered to 10 men and 10 women without history of low back disorder via a cable attached to a thoracic harness; motion was restricted to the lumbar spine. Results indicate that gender was not a significant factor in this study. The lifting belt reduced the peak normalized EMG of th e erector spinae muscles on average by 3% during asymmetric loading, though peak normalized EMG was increased by 2% during symmetric loading. Lifting belts have been shown to slightly reduce peak erector spinae activity during asymmetric sudden loading events in a constrained paradigm; however, the effects of lifting belts are too small to provide effective protection of workers. Actual or potential applications include the assessment of lifting belts as protective devices in workers based on the effects of lifting belts on the trunk muscle activity.

INTRODUCTION

Material handling tasks have been cited as the most frequent cause of work-related low-back injuries (Andersson, 1981; Bigos et al., 1986), and forceful movements or sudden maximal exertions have been associated with the onset of these injuries (Bigos et al., 1986; Magora, 1973; Troup, Martin, & Lloyd, 1981). Sudden maximal exertions often result from slips, falls, or lifting of unstable loads (e.g., a container partially filled with liquid). Relative to expected loading, unexpected loading of the torso has been associated with greater trunk displacement, increased trunk muscle activity (Caldwell et al., 1974; Cresswell, Oddsson, & Thorstensson, 1994; Marras, Rangarajulu, & Lavender, 1987), and faster-onset rate of trunk muscle activity (Lavender et al., 1989; Lavender, Marras, & Miller, 1993; Marras et al., 1987).

Although the effects of lifting belts on spine biomechanics are not fully understood (National Institute for Occupational Safety and Health, Back Belt Working Group, 1994), there is some evidence that lifting belts restrict trunk motion and, hence, may protect the spine during unexpected loading. McGill, Seguin, and Barnett (1994) measured the effect of lifting belts on passive motion of the spine in three planes and reported that the lifting belt increased the passive stiffness of the trunk in the frontal and transverse planes. Additionally, Lavender, Thomas, Chang, and Andersson (1995) reported that lifting belts reduce trunk side bending and rotation (twisting) during asymmetric lifting tasks when foot motion is restricted. The reduced motion suggests that a lifting belt increases trunk stiffness, which could be expected to reduce the trunk displacement during a sudden perturbation. We have hypothesized that lifting belts help protect the spine by decreasing the magnitude of trunk muscle response necessar y to restore equilibrium to the system following a sudden loading event. Therefore, the purpose of this paper was to investigate the effects of lifting belts on trunk muscular and kinematic responses to a sudden loading event in men and women.

METHODS

Participants

Twenty participants (10 men and 10 women), 20 to 33 years of age, signed an informed consent form approved by two institutional review boards. The participants were screened for a history previous or ongoing low-back pain (LBP). …

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