The influence of psychosocial stress, gender, and personality on mechanical loading of the lumbar spine

Study Design. 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. Summary of Background Data. 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 trails. 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.