Long term occupational exposure to whole-body vibration (WBV) can have detrimental effects on the worker. Although our bodies are capable of harmlessly attenuating most vibrations, frequencies between 1-20 Hz can cause resonance in the spine and pelvis leading to negative health effects such as low back pain. Various standards have been set in place to provide recommendations for safe exposure limits. In North America, the ISO 2631-1 is the standard by which most organizations make their assessments. Vehicle operators in the mining sector have the potential for exposure to hazardous levels of WBV due to off-road driving, long shifts, and improper seat design. Previous research has shown individuals who are regularly exposed to high levels of WBV have an increased risk of suffering from low back pain (LBP).

Operators of surface haulage truck vehicles are exposed to WBV and static postures for up to 10 hours each day. Recent statistics from the Ontario Mining Industry reveal that up to 30% of operators suffer from low back pain of at least moderate severity. One of the challenges in dealing with LBP is that the origin of this symptom is often multifactorial and thus the exact epidemiological nature of individual injuries is complex and elusive. This research explores a possible mechanism for LBP in an attempt to make the picture clearer.

Proprioception is a submodality of somatosensation and it involves the collection of afferent information from mechanoreceptors in and around the joint by the central nervous system to track both positional and kinesthetic information about a joint segment. The CNS processes this information and in turn conducts an orchestra of muscle contraction that will provide optimal joint stability in a given situation. There is evidence that WBV exposure fatigues the muscles due to a series of synchronous contractions. Fatigued muscles are less effective at providing the CNS with accurate positional information. In the absence of quality afferent information, stability is compromised leading to increased risk of injury.

WBV was measured on 8 surface haulage trucks in three size classes (35, 100, 150 ton haul capacities). Vibration was measured at the seat/operator interface in accordance with the ISO 2631-1 standard during 1 hour of normal operation. Highest acceleration readings were observed in the z-axis (vertical). Estimated equivalent daily exposure values in the range of 0.44-0.82 m/s² were observed using the frequency-weighted r.m.s method and 8.7-16.4 m/s^1.75 using the vibration dose value method. Smaller truck sizes were typically associated with higher vibration than larger trucks. This research confirmed that operators of surface haulage trucks are regularly exposed to WBV levels that exceed safety limits as dictated by the ISO 2631-1 standard.

The effect of this exposure on lumbar proprioception was studied by comparing lumbar spine reposition sense before and after exposure to WBV at levels comparable to field measurements. Lumbar angle was calculated along three axes (flexion, lateral bend, and rotation) using a 3D motion capture system. Subjects were tested in both a seated and standing posture and measurements were repeated on two separate days. On day one, subjects received 45 minutes of WBV exposure (0.7 m/s² wRMS, at 3 Hz) as a treatment. On day two, a control treatment of 45 minutes of static sitting was employed. The results did not reveal any significant loss of lumbar proprioception after either vibration exposure or static sitting. Repositioning accuracy was lower during sitting rather than standing tests and the x-axis (axis of flexion) was associated with significantly higher error than the y or z-axes (lateral bend and rotational axes respectively).

The findings from this report suggest that proprioception is not affected by 45 minutes of WBV exposure at levels typical to the operation of surface haulage trucks and thus inhibited lumbar position sense is not likely a contributor to the development of LBP under these circumstances.