Neuromotor transmissibility of horizontal seatpan vibration

Abstract

Exposure to occupational whole body vibration (WBV) is associated with low back pain disorders, musculoskeletal disorders, and degeneration of spine. Transmission of vibration to the neuromotor system may play a role in the etiology of these injuries. Such WBV has components in the vertical, lateral and fore-aft directions. However, few studies have examined biodynamic vibration transmission in the fore-aft direction and no study has examined transmission of fore-aft vibration to the neuromotor system. The primary objective of this study was to assess the response characteristics of the fore-aft seatpan vibration. A secondary objective was to examine the effect of a backrest on these characteristics. Nineteen subjects participated in the study (10 male, 9 female, mean age 24 ± 3 (SD) years, height 1.6 ± .05 m (SD), weight 69 ± 7 kg (SD)). The transmission of vibration to vibration-induced lumbar rotation (TF2) and paraspinal muscle activity (TF3), with and without the backrest, were quantified for a frequency range of 3-14 Hz at 1 RMS (ms -2) and 2 RMS (ms-2) vibration magnitudes. The mechanical transmission to lumbar rotations did not exhibit resonance within the measured frequency range without the backrest. The mechanical transmission with a backrest exhibited a ratio greater than one between 3-6 Hz indicating a resonance phenomena. Mechano-neuromotor transmission, the relationship between lumbar rotation and paraspinal muscle activity (TF4), without the backrest, exhibited a double peaked trend with a primary peak at 5-6 Hz and a secondary peak at 11 Hz. The primary peak at 5-6 Hz may be a result of coupled vertical motion and the 11 Hz might correspond to the internal resonance of the neuromuscular system. The small peaks at 6, 10 and 12 Hz for 1 RMS (ms-2) and a larger peak at 8 Hz for 2 RMS (ms-2) were exhibited in TF4 with the backrest. The peaks at 6 and 8 Hz may be a result of coupled vertical motion or a result of external stimulating agent. The secondary peaks might be a result of internal resonance of the neuromuscular system. These results can be used in experiments examining the effects of fore-aft WBV on neuromotor habitation and muscular fatigue.