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The Impact of Mental Processing and Pacing on Spine Loading: 2002 Volvo Award in Biomechanics

Davis, Kermit G., PhD*†,; Marras, William S., PhD†,; Heaney, Catherine A., PhD‡,; Waters, Thomas R., PhD§,; Gupta, Purnendu, MD


Study Design. The impact of various levels of mental processing and pacing (during lifting) on spine loading was monitored under laboratory conditions.

Objectives. To explore how mental demands and pacing influence the biomechanical response and subsequent spine loading and, to determine whether individual characteristics have a modifying role in the responses.

Summary of Background Data. Modern work often requires rapid physical exertions along with demands of mental processing (both psychosocial stressors). While the effect of physical workplace factors on spine loading has been widely documented, few studies have investigated the impact that interaction of psychosocial factors and individual factors has on spine loads.

Methods. For this study, 60 subjects lifted boxes while completing two types of mental processing tasks: 1) series tasks with decisions occurring before the act of lifting, and 2) simultaneous tasks with decisions occurring concurrently with the lift. For both of these mental processing conditions, two intensities of mental load were evaluated: simple and complex. Task pacing was also adjusted under slow and fast conditions. Finally, individual characteristics (personality and gender) were evaluated as potential modifiers. An electromyographically assisted model evaluated the three-dimensional spine loads under the experimental conditions.

Results. Simultaneous mental processing had the largest impact on the spine loads, with the complex intensity resulting in increases of 160 N with lateral shear, 80 N with anteroposterior shear, and 700 N with compression. Increased task pace produced greater lateral shear (by 20 N), anteroposterior shear (by 60 N), and compression loads (by 410 N). Gender and personality also influenced loadings by as much as 17%.

Conclusions. Mental processing stress acted as a catalyst for the biomechanical responses, leading to intensified spine loading. Mental stress appeared to occur as a function of time pressures on task performance and resulted in less controlled movements and increases in trunk muscle coactivation. These adjustments significantly increased spine loading. These results suggest a potential mechanism for the increase in low back pain risk resulting from psychosocial stress caused by modern work demands.

From the *Department of Environmental Health, University of Cincinnati, Ohio,

the †Biodynamics Laboratory

and the ‡School of Public Health, Ohio State University, Columbus, Ohio,

the §National Institute for Occupational Safety and Health, Cincinnati, Ohio,

and the ∥Section of Orthopaedic Surgery and Rehabilitation Medicine, University of Chicago, Illinois.

Partial funding for this project was generously provided by Honda of America and the International Society for Biomcehanics.

Device status category: The submitted manuscript does not contain information about medical devices and drugs.

Conflict of interest category: Corporate, industry, and professional organizational funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address reprint requests to William S. Marras, PhD, Biodynamics Laboratory, Ohio State University, 1971 Neil Avenue, Columbus, OH 43210. E-mail:

© 2002 Lippincott Williams & Wilkins, Inc.