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The purpose of this study was to evaluate the efficacy of multi-axial (lateral + vertical) active suspension in reducing multi-axial WBV exposures and related biomechanical loading in the neck and low back as compared to an industry standard single-axial (vertical) passive suspension seat. In a repeated-measures laboratory study with 13 subjects, while recreating field-measure vehicle vibration on a 6-degree-of-freedom motion platform, we measured WBV [weighted average vibration: A(8) and vibration dose values: VDV(8)], net joint torque in the low back (L5/S1) and neck, muscle activity in low back (erector spinae) and neck muscle (splenius capitis). The results showed that the multi-axial active suspension seat was more effective in reducing vertical (Z-axis) WBV [A(8) and VDV(8)] as compared to the single-axial passive suspension seats (p < 0.001), while little difference between two suspension seats were found in lateral (Y) axis. The peak low back moment with respect to the sagittal (Y) axis was significantly lower on the multi-axial active suspension seat compared to the single-axial passive suspension seat (p=0.01). Despite lack of statistical significance, the low back and neck muscle activity tended to be lower on the multi-axial active suspension compared to the single-axial passive suspension. These results indicate that the multi-axial suspension may have potential to reduce biomechanical loading in the low back.

Whole-body vibration (WBV) is known to be a leading factor for developing musculoskeletal disorders (MSDs). As mining vehicle operators are exposed to frequent transient shocks and substantial non-vertical WBV exposures, they may be at a greater risk than on-road vehicle operators. However, the impact of such exposures is not well understood. Therefore, this study aimed to evaluate how the exposure to WBV affected physiological stress and whether mining vehicles’ vibration with substantial non-vertical WBV components would further increase the level of physiological stress as compared to on-road vehicle vibration (vertical-axis dominant vibration). In a repeated-measures laboratory study, a 6-degree-of-freedom motion platform was used to recreate three different types of field-collected vibration profiles: vertical-axis dominant vibration measured from on-road long-haul trucks (VA), multi-axial vibration measured from mining vehicles (MA), and no vibration (control condition: CC). Subjects were exposed to each vibration condition for 2-hour sessions over three different experimental days. Blood samples were collected before and after each exposure session in order to measure biological markers for inflammation (tumor necrosis factor-α: TNFα), muscle damage (creatine kinase), and physiological stress (cortisol). During the 2-hour WBV exposures, muscle activity in the neck and low back muscles was measured using electromyography. The results showed that there were statistically significant differences in TNFα (inflammatory response) levels between vibration exposure (VA and MA) and the control condition (no vibration) (p = 0.01); however, these differences are not considered as clinically significant changes. No significant changes were found in muscle damage (creatine kinase) and physiological stress (cortisol). The vibration exposure conditions (VA and MA) showed higher low back muscle activity; however, these differences did not reach statistical significance (p’s > 0.08). Neck muscle activity did not differ among exposure conditions. The lack of effect in these results may support previous findings that MSDs develop from prolonged exposure to WBV and not from acute exposure to physical risk factors.

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