The effect of personality and behaviour on muscle co-contraction ratios In the trunk when people are exposed to different types of emotional stimuli while performing a lateral bend and simple lifting task

Abstract

Psychosocial factors have long been implicated in occupational injury risk, but the nature of this relationship is obscure. Recent investigations have concluded that emotional responses affect muscle force outputs; which may, in turn, affect joint loading. Personality type has also been shown to affect joint loading (Marras et al., 2000). Likewise, there is an interaction between emotional stimuli and personality. Exposure to pleasant emotional stimuli has been shown to facilitate flexion movements; whereas exposure to unpleasant emotional stimuli has been shown to facilitate extension movements (Coombes et al., 2008). However, it is not clear what co-contraction ratio, and consequently what joint load, any given emotional stimulus might result in, or how personality variables might affect this relationship. To address this, participants filled out an International Personality Inventory Pool (IPIP) Survey and a Behaviour Activation System and Behaviour Inhibition System (BAS/BIS) Survey to determine each participant’s specific personality and behaviour traits. Participants were then exposed to emotional stimuli prior to a torso lateral bend, requiring both flexor and extensor cocontraction. A total of 29 participants were tested. Participants were randomly exposed to unpleasant, neutral, pleasant, and colour image types; 30 images in total. They were exposed to these images for five seconds, then a tone sounded after which they initiated a lateral bend. The current results indicate that image type had no significant effect on flexor/extensor and left/right side co-contraction ratios. Varying levels of personality and behaviour were the only factors to produce significantly different co-contraction ratios. There was also a significant difference vi of left/right side co-contraction ratios between men and women, where men had produce significantly greater right side dominant co-contraction ratios for all image types compared to women. The second part of the experiment had subjects stand on a force-plate and listen to different types of emotional sounds. These sounds ranged from unpleasant, pleasant, and neutral. Subjects would listen to a specific emotional sound for six seconds, and after the sound was over, a voice would inform them to lift a 15 pound crate off of the floor in front of them and place it on a table waist height. The second sound would have subjects pick up the crate from the table and place it back on the ground. This was done a total of 30 times with 30 different sounds. The results indicate that sound type had no significant effect on cocontraction ratios. Varying levels of personality and behaviour were the only factors to produce significant changes in co-contraction ratios for both flexor/extensor and left/right side co-contraction ratios. There were also significant changes between co-contraction ratios and sex. Both men and women produced flexor dominated co-contraction ratios for all sound types, but men produced significantly higher flexor dominated co-contraction ratios for all sound types compared to women. Men also produced significantly greater right side dominant co-contraction ratios, compared to women, for all sound types.