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The aim of this study is to investigate the effects on upper limb and lower back muscles activities during prolonged sitting in two different work area boundaries. The effects are measured from the muscle activities of subjects performing two repetitive tasks at the near work area boundary and at the far work area boundary. Subjects consisted of 10 males (age 27.7?5.42) and 10 females (age 27.5?5.91) with no history of musculoskeletal injury or back problem at the time of participation. Surface electromyography (sEMG) signal were recorded from the right and left Levator Scapulae, Upper Trapezius, Anterior Deltoid and Erector Spinae which are known as the weaken and tighten muscles due to musculoskeletal disorders (MSD). The EMG signal was processed and normalized in the form of % MVC for analysis. The overall results indicated that muscle activities in the upper limb and lower back increased significantly when performing work at the far work area boundary. The most active muscle is the Left Erector Spinae (2.37% MVC at the near, 2.91% MVC at the far work area boundary), while the lowest active muscle is the Left Anterior Deltoid (0.09% MVC at the near, 0.13% MVC at the far work area boundary). The muscle activity at the far work area boundary is on average 17% greater than at the near work area boundary. Females showed greater muscular activity compared to males at the near (average difference, 1.28 % MVC) and at the far work area boundary (average difference, 1.56% MVC). The result of independent sample t-test showed significant differences on muscle activities at the near and at the far work area boundary between males and females. The results above indicate the importance to predict the muscle activity and time to fatigue. A regression equation model to predict muscle activity and time to fatigue is developed in this research.