The influence of psychosocial stress, gender, and personality on mechanical loading of the lumbar spine.
METHODS
The effects of psychosocial stress on muscle activity and spinal loading were evaluated in a laboratory setting.


OBJECTIVE
To evaluate the influence of psychosocial stress, gender, and personality traits on the functioning of the biomechanical system and subsequent spine loading.


BACKGROUND
Physical, psychosocial, and individual factors all have been identified as potential causal factors of low back disorders. How these factors interact to alter the loading of the spine has not been investigated.


METHODS
Twenty-five subjects performed sagittally symmetric lifts under stressful and nonstressful conditions. Trunk muscle activity, kinematics, and kinetics were used to evaluate three-dimensional spine loading using an electromyographic-assisted biomechanical model. A personality inventory characterized the subject's personality traits. Anxiety inventories and blood pressure confirmed reactions to stress.


RESULTS
Psychosocial stress increased spine compression and lateral shear, but not in all subjects. Differences in muscle coactivation accounted for these stress reactions. Gender also influenced spine loading; Women's anterior-posterior shear forces increased in response to stress, whereas men's decreased. Certain personality traits were associated with increased spine loading compared with those with an opposing personality trait and explained loading differences between subjects.


CONCLUSIONS
A potential pathway between psychosocial stress and spine loading has been identified that may explain how psychosocial stress increases risk of low back disorders. Psychosocially stressful environments solicited more of a coactivity response in people with certain personality traits, making them more susceptible to spine loading increases and suspected low back disorder risk.
Marras
W S
WS
Biodynamics Laboratory and the School of Public Health, The Ohio State University, Columbus, Ohio 43210, USA. marras.1@osu.edu
Davis
K G
KG
Heaney
C A
CA
Maronitis
A B
AB
Allread
W G
WG
D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006615:Hip / Q000502:physiology; D006801:Humans; D017770:Lifting; D017116:Low Back Pain / Q000503:physiopathology / Q000523:psychology; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D010551:Personality; D012307:Risk Factors; D012737:Sex Factors; D013315:Stress, Psychological / Q000503:physiopathology*; D016474:Weight-Bearing / Q000502:physiology