Muscle activity and range of motion during active trunk rotation in a sitting posture

Twisted trunk postures during tractor driving are associated with low-back pain. The purposes of this study were to quantify the muscle activity as a function of twisting angle, to quantify the range of motion (ROM) during ac tive trunk rotation and to determine whether there were any differences bet ween tractor drivers and office workers and between twisting direction for these variables. The subjects performed exertions in a seated position, twi sting from the neutral position to the end of the ROM. The results showed t hat external oblique and erector spinae had significantly different activat ion patterns depending on twisting direction. For the contralateral externa l oblique and the ipsilateral erector spinae, the muscle effort required to twist the trunk was low up to about 20 degrees twisting angle, then the mu scle effort needed to twist the trunk increased progressively. No significa nt differences due to occupation or twisting direction were found. The resu lt implies that work in twisted trunk postures might be a risk factor for l ow-back pain. (C) 2001 Elsevier Science Ltd. All rights reserved.