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Background: Lower back and neck pain is common among persons who drive vehicles in their profession. The vehicle occupants are exposed to whole-body vibration (WBV) that may include mechanical shocks which are believed to increase the likelihood of injury further. Mechanical shocks are especially generated when driving on rough terrain and may challenge drivers' postural equilibrium. Little is known about the contribution of postural load to injury risk and thus objective measurements are necessary.

Purpose: The purpose of the study was to assess the feasibility of registering and analyzing seated postural load and shock-type WBV synchronously using inertial measurement units (IMUs) among drivers of forest machines during terrain-like conditions.

Methods: Five male participants (18-34 years old) drove a forest machine 6 times over three different standardized steal obstacles along a gravel course using a predefined speed and posture. Participants then drove the same vehicle 3 times over natural obstacles along a terrain course using a self-selected speed and posture. Three IMUs were affixed along the spine (at S2, Th2 and C4) and one to the head of participants as well as one to the seat. Data from the IMUs regarding accelerations and orientation in sagittal, frontal and horizontal plane were then analyzed.

Results: Postural load, expressed as the range of motions (ROMs) in the upper neck, lower neck, trunk and pelvis were less than 22° in all directions during maneuvers on the standardized course. The size of obstacle and the vehicle speed had significant effects on the ROMs. No significant differences between courses were evident regarding seat accelerations and angular velocities at the drivers head. The WBV analysis of the terrain course indicated that mechanical shocks were prevalent but exceeded the exposure action value for only one driver and not the exposure limit value according to health and safety requirements within the European Union (EU directive 2002/44/EC).

Conclusion(s): IMUs may objectively be used to register and present seated postural load and shock-type WBV exposure synchronously when driving on terrain. There seems to be a low risk of injuries from mechanical shocks since the magnitude of postural load (ROMs) during tested conditions was not considered to increase injury risk even though vehicle speed and the size of obstacles had a significant effect.

Implications: Postural load when driving a forest machine during terrain-like conditions appears low in this study but more long-term field measurements on more drivers are needed before definite conclusions can be made. IMUs are regarded as promising tools for registering and representing seated postural load and shock-type WBV exposure. Future development could provide drivers with feedback regarding potentially injurious postures and/or high shock-type WBV exposure.