Comparison of Upper Extremity Muscle Activity With Transverse Plane Angle Changes During Vertical Keyboard Typing

타이핑 작업 시 수직형 키보드의 수평면 끼인각 변화에 따른 상지의 근활성도 비교

  • Lee, Kang-Jin (Dept. of Physical Therapy, The Graduate School, Hanseo University, Gochang Hyundai Clinic) ;
  • Roh, Jung-Suk (Dept. of Physical Therapy, Hanseo University) ;
  • Kim, Tack-Hoon (Dept. of Physical Therapy, Hanseo University) ;
  • Cynn, Heon-Seock (Dept. of Physical Therapy, Hanseo University) ;
  • Choi, Houng-Sik (Dept. of Physical Therapy, Hanseo University) ;
  • Oh, Dong-Sik (Dept. of Physical Therapy, Hanseo University)
  • 이강진 (한서대학교 대학원 물리치료학과, 고창현대의원 물리치료실) ;
  • 노정석 (한서대학교 물리치료학과) ;
  • 김택훈 (한서대학교 물리치료학과) ;
  • 신헌석 (한서대학교 물리치료학과) ;
  • 최흥식 (한서대학교 물리치료학과) ;
  • 오동식 (한서대학교 물리치료학과)
  • Published : 2009.05.21


In order to prevent upper extremity musculoskeletal disorders, effective keyboard selection is an important consideration. The aim of this study was to compare upper extremity muscle activity according to transverse plane angle changes during vertical keyboard typing. Sixteen healthy men were recruited. All subjects had a similar typing ability (rate of more than 300 keystrokes per minute) and biacromion and forearm-fingertip lengths. Four different types of keyboard (vertical keyboard with a transverse plane angle of $60^{\circ}$, $96^{\circ}$, or $120^{\circ}$, and a standard keyboard) were used with a wrist support. The test order was selected randomly for each subject. Surface electromyography (EMG) was used to measure upper extremity muscle activity during a keyboard typing task. The collected EMG data were normalized using the reference contraction and expressed as a percentage of the reference voluntary contraction (%RVC). In order to analyze the differences in EMG data, a repeated one-way analysis of variance, with a significance level of .05, was used. Bonferroni correction was used for multiple comparisons. There were significant differences in the EMG amplitude of all seven muscles (upper trapezius, middle deltoid, anterior deltoid, extensor carpi radialis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris) assessed during the keyboard typing task. The mean activity of each muscle had a tendency to increase as the transverse plane angle increased. The mean activity recorded during all vertical keyboard typing was lower than that recorded during standard keyboard typing. There was no significant difference in accuracy and error scores; however, there was a significant difference between transverse plane angles of $60^{\circ}$ and $120^{\circ}$ with regard to comfort. In conclusion, a vertical keyboard with a transverse plane angle of $60^{\circ}$ would be effective in reducing muscle activity compared with vertical keyboards with other transverse plane angles.


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