Perceived body discomfort and trunk muscle activity in three prolonged sitting postures

[Purpose] This study aimed to investigate the perceived discomfort and trunk muscleactivity in three different 1-hour sitting postures. [Subjects] A repeated-measures designstudy was conducted on 10 healthy subjects. [Methods] Each subject sat for an hour inthree sitting postures (i.e., upright, slumped, and forward leaning sitting postures).Subjects rated perceived body discomfort using Borg’s CR-10 scale at the beginning andafter 1 hour sitting. The electromyographic activity of the trunk muscle activity wasrecorded during the 1-hour period of sitting. [Results] The forward leaning sittingposture led to higher Borg scores in the low back than those in the upright (p = 0.002)and slumped sitting postures (p < 0.001). The forward leaning posture was significantlyassociated with increased iliocostalis lumborum pars thoracis (ICL) and superficial lumbarmultifidus (MF) muscle activity compared with the upright and slumped sitting postures.The upright sitting posture was significantly associated with increased internal oblique(IO)/transversus abdominis (TrA) and ICL muscle activity compared with the slumped sittingposture. [Conclusion] The sitting posture with the highest low back discomfort afterprolonged sitting was the forward leaning posture. Sitting in an upright posture isrecommended because it increases IO/TrA muscle activation and induces only relativelymoderate ICL and MF muscle activation.Key words: Pain, Sitting posture, Electromyography