Affiliations: Department of Rehabilitation Therapy, The Graduate
School, Yonsei University, Republic of Korea | Department of Physical Therapy, College of Health
Science, Yonsei University, Republic of Korea
Note: [] Address for correspondence: Chung-hwi Yi, Department of Physical
Therapy, College of Health Science, Yonsei University, 234, Maeji-ri,
Heungup-myun, Wonju, Kangwon-do, 220-710, Republic of Korea. Tel.: +82 33 760
2429; E-mail: pteagle@yonsei.ac.kr
Abstract: This study examined the effect of a ball-backrest chair on the
weakness and tightness of muscles associated with upper crossed syndrome when
working at a visual display terminal (VDT). The surface electromyography (EMG)
was recorded from the serratus anterior, middle trapezius, and upper trapezius
muscles of 20 adults as they performed VDT work, which are known as the
weakened and tightened muscles of upper crossed syndrome. The recorded signals
were averaged and normalized to the mean amplitude of the EMG signal obtained
during submaximal reference voluntary contractions. The significance of
differences between the use of a general-purpose backrest and a ball backrest
was tested by paired t-test, with the significance cutoff
set at α=0.05. The activities of the serratus
anterior and middle trapezius muscles increased and that of the upper trapezius
muscle decreased when sitting in a ball-backrest chair compared to when sitting
in a chair with a general-purpose backrest (p<0.05). These
results indicate that the use of a ball-backrest chair reduces the risk of
patients with upper crossed syndrome developing muscles soreness or injury
related to overuse when working at a VDT.
