Abstract:Occupational whole body vibration has long been associated with low back injuries.However, the mechanism of these injuries is not well understood. In this paper, the effect of whole body vibration on proprioception and dynamic stability was examined. Subjects exposed to 20 minutes of vertical, seated, whole body vibration were found to have a 1.58 fold increase in position sense errors after vibration relative to controls exposed to 20 minutes of the same seated posture without vibration exposure. To understand the potential effect of a sensory loss on dynamic low back stability a lumped parameter model of the trunk and neuromotor response was created. Using this model, an increase in the threshold of the sensory system was predicted to increase trunk flexion and delay neuromotor response with a sudden, unexpected perturbation. These predictions were demonstrated in a second experiment where subjects exhibited both an 11.9% increase in trunk flexion and an 11.2% increase in time to peak paraspinal muscle response (measured using integrated electromyographic activity) after exposure to 20 minutes of vertical, seated, whole body vibration.

Low back disorders are very common affecting up to 80% of the population in their lifetime [1]. Whole body vibration (WBV) exposure has long been identified as an important risk factor for low back disorders in industrial workers [2]. A potential mechanism has been proposed by which vibration may lead to injury. Namely, vibration-induced losses in proprioception may lead to inappropriate stabilization and poor dynamic control of the lumbar spine [3]. Increases in proprioceptive errors and in delays in neuormotor response have been demonstrated with 5 Hz, vertical seatpan vibration [3]. While vertical vibration exposure is a common occupational exposure, in some cases, such as off road vehicles and construction vehicles horizontal (fore-aft) vibration may dominate [4]. In this study, the objective was to investigate how the whole body, horizontal, seatpan vibration affects muscle response and to compare these results with the previously studied whole body vertical vibration.