This research was aimed at defining the extent of oculo-manual tracking performance degradation due to hand vibration. Changes in tracking performance were evaluated using process identification. The contribution of the nonlinear component to the eye/hand response was used as an indicator of the effects of vibration on each tracking system. The results indicated that during hand vibration the eye and hand remnants increase. Vibration-induced alterations of the proprioceptive system, and thus the sensorimotor control loops, are suggested to be the primary cause of remnant increase.< >
The effects of treadmill workstation use on kinematic gait symmetry and computer work performance remain unclear. The purpose of this pilot study was to analyze the effects of treadmill workstation use on lower body motion symmetry while performing a typing task when compared to overground and treadmill walking. The lower body motion of ten healthy adults (6 males and 4 females) was recorded by a motion capture system. Hip, knee, and ankle joint rotations were computed and compared for each condition. Despite comparable lower body kinematic gait asymmetries across conditions, asymmetric knee flexion motions at early gait cycle were only found in treadmill workstation users (left knee significantly more flexed than the right one). This demonstrates that the interaction between walking and another task is dependent on the task cognitive content. Our findings suggest that lower body kinematic gait symmetry may be influenced by the use of treadmill workstations.
Abstract Background Control of reaching movements for manual work, vehicle operation, or interactions with manual interfaces requires concurrent gaze control for visual guidance of the hand. We hypothesize that reaching movements are based on negotiated strategies to resolve possible conflicting demands placed on body segments shared by the visual (gaze) and manual (hand) control systems. Further, we hypothesize that a multiplicity of possible spatial configurations (redundancy) in a movement system enables a resolution of conflicting demands that does not require sacrificing the goals of the two systems. Methods The simultaneous control of manual reach and gaze during seated reaching movements was simulated by solving an inverse kinematics model wherein joint trajectories were estimated from a set of recorded hand and head movements. A secondary objective function, termed negotiation function , was introduced to describe a means for the manual reach and gaze directing systems to balance independent goals against (possibly competing) demands for shared resources, namely the torso movement. For both systems, the trade-off may be resolved without sacrificing goal achievement by taking advantage of redundant degrees of freedom. Estimated joint trajectories were then compared to joint movement recordings from ten participants. Joint angles were predicted with and without the negotiation function in place, and model accuracy was determined using the root-mean-square errors (RMSEs) and differences between estimated and recorded joint angles. Results The prediction accuracy was generally improved when negotiation was included: the negotiated control reduced RMSE by 16% and 30% on average when compared to the systems with only manual or visual control, respectively. Furthermore, the RMSE in the negotiated control system tended to improve with torso movement amplitude. Conclusions The proposed model describes how multiple systems cooperate to perform goal-directed human movements when those movements draw upon shared resources. Allocation of shared resources can be undertaken by a negotiation process that is aware of redundancies and the existence of multiple solutions within the individual systems.
Existing ergonomic assessment tools have been designed for routine and structured work making their use in informal work setting challenging due to the high variability in tasks performed by informal workers. The Ergonomic Assessment tool for Unstructured Work (EAUW) was developed by Acquah and colleagues to address this challenge. The tool is efficient and has good inter-observer reliability, but little information is known about its other psychometric properties. This paper assesses the reliability and validity of EAUW. Criterion validity was determined by comparing the EAUW with existing tools for a selected number of e-waste recycling tasks. Intra-observer reliability was determined by comparing observations from the same assessor 5 days apart. Results indicated a high intra-observer agreement for all exposure variables. Compared to existing tools which provide a snapshot of ergonomic exposures, the EAUW provides a more detailed estimate of work exposures between- and within-workers across time.