Analysis of Biodynamic Responses Associated with Upper Limb Reaching Movements under Whole-Body Vibration: Support for an Active Biodynamic Model.

Abstract

Vehicle vibration is a well-recognized environmental stressor inducing discomfort, health risks, and performance degradation of the operator on board. More specifically, vibration transmitted by heavy transportation, construction, or military vehicles to the whole body of a seated occupant interferes with manual activities, which in turn may significantly compromise performance. Numerous approaches have attempted to understand the effects of vibration on the seated human for developing biomechanical models or to identify human reaching behaviors for developing human movement models. However, all these studies were limited to biomechanical models of the torso excluding the upper limbs, or to reach models based only on static conditions with no consideration of the interaction between environmental conditions of vibration and biodynamic characteristics of arm movements. The ultimate goal of this work is to provide a framework for an active biodynamic model of operators in vehicles based on empirical analyses of biodynamic responses of seated humans performing reaching movements under simplified whole-body vibration conditions. Hence, the present work investigates vibration transmission through multi-body segments as a function of vibration frequency and direction, identifies vibration-induced changes in reach kinematics of upper arm movements, analyzes the mechanisms of vibration transmission through a multi-body system as a function of posture and movement coordination, and proposes the integration of these empirical results for developing a biodynamic model. Five major results characterize our findings: a) vibration frequency is the dominant factor determining transmission characteristics through upper body segments, b) reach directions in three-dimensional space may be divided into three groups corresponding to transmission propagated through the upper limbs, c) visual compensation contributes to hand stabilization but does not modify significantly propagated transmission, d) elbow flexion contributes to the enhancement of hand stabilization by dissipating vibration energy, and e) biodynamic responses must be considered as three-dimensional tensors including the auto-axial and cross-axial transmissions. Furthermore, movement coordination and joint movement kinematics of reach movements are consistent between static and vibratory environments. The integration of these results may be used to support the structure of an active biodynamic model of the seated human.