Effects of a Lumbar Belt on Neuromotor Transmission of Whole Body Vibration

Abstract

Whole body vibration (WBV) has been identified as a risk factor for low back musculoskeletal disorders and injuries. One potential mechanism by which WBV may lead to low back injury is through stimulation of muscle spindle organs and repetitive activation of the stretch-reflex neuromotor response. Such repetitive activation could lead to muscular fatigue and/or neuromotor adaptation. Understanding mechanical transmission of vibration to the neuromotor system and the resulting neuromotor activation is critical to understanding these mechanisms. In this study, it was theorized that activation of the extensor musculature of the low back is a response to the lengthening and shortening of the extensor musculature. This lengthening and shortening of the extensor musculature may be the result of flexion-extension rotation in the lumbar spine. By measuring lumbar flexion and extension, the amplitude and phase of this lengthening and shortening were assessed. Using electromyographic data from the erector spinae muscle groups at the L2/L3 lumbar level, the cyclic activation of the extensor musculature was also measured. Neuromotor transmission was observed over a frequency range of 3–20 Hz and vibration magnitudes of 1 and 2 m/s^2 RMS. Resonance peaks in lumbar flexion-extension and the integrated electromyographic data were observed at 4 Hz and 10–12 Hz. A lumbar belt was used to reduce transmission of axial seat-pan vibration to lumbar flexion-extension and to observe the changes in cyclic electromyographic activity. The lumbar belt was found to decrease both lumbar flexion-extension and paraspinal muscle activity demonstrating a link between axial seatpan vibration, lumbar flexion-extension and the cyclic activation of the neuromotor system. These results provide information on the neuromotor effects of WBV and may be used to design better low back injury prevention methods.