Internal Oblique and Transversus Abdominis Muscle Fatigue Induced by Slumped Sitting Posture after 1 Hour of Sitting in Office Workers.

BACKGROUND Prolonged sitting leads to low back discomfort and lumbopelvic muscle fatigue. This study examined the characteristics of body perceived discomfort and trunk muscle fatigue during 1 hour of sitting in three postures in office workers. METHODS Thirty workers sat for 1 hour in one of three sitting postures (i.e., upright, slumped, and forward leaning postures). Body discomfort was assessed using the Body Perceived Discomfort scale at the beginning and after 1 hour of sitting. Electromyographic (EMG) signals were recorded from superficial lumbar multifidus, iliocostalis lumborum pars thoracis, internal oblique (IO)/transversus abdominis (TrA), and rectus abdominis muscles during 1 hour of sitting. The median frequency (MDF) of the EMG power spectrum was calculated. RESULTS Regardless of the sitting posture, the Body Perceived Discomfort scores in the neck, shoulder, upper back, low back, and buttock significantly increased after 1 hour of sitting compared with baseline values (t (9) = -11.97 to -2.69, p < 0.05). The MDF value of the EMG signal of rectus abdominis, iliocostalis lumborum pars thoracis, and multifidus muscles was unchanged over time in all three sitting postures. Only the right and left IO/TrA in the slumped sitting posture was significantly associated with decreased MDF over time (p = 0.019 to 0.041). CONCLUSION Prolonged sitting led to increased body discomfort in the neck, shoulder, upper back, low back, and buttock. No sign of trunk muscle fatigue was detected over 1 hour of sitting in the upright and forward leaning postures. Prolonged slumped sitting may relate to IO/TrA muscle fatigue, which may compromise the stability of the spine, making it susceptible to injury.