| dc.description.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. | en_US |
