hayati Mohd Nur

The effects of energy expenditure rate on work productivity performance at different levels of production standard time.

[Purpose] The purpose of this study was to investigate the effects of energy expenditure rate on work productivity performance at different levels of production standard time. [Subjects and Methods] Twenty industrial workers performed repetitive tasks at three different levels of production standard time, normal, hard, and very hard. Work productivity and energy expenditure rate were recorded during the experimental tasks. [Results] The work productivity target was not attainable for the hard and very hard production standard times. This was attributed to the energy expenditure rate, which increased as the level of production standard time became harder. The percentage change in energy expenditure rate for the very hard level (32.5%) relative to the normal level was twice that of the hard level (15.5%), indicating a higher risk of work-related musculoskeletal disorders for the harder production standard time. The energy expenditure rate for the very hard production standard time (1.36 kcal/min) was found to exceed the maximum energy expenditure rate recommended for light repetitive tasks involving both arms (1.2 kcal/min). [Conclusion] The present study shows that working with an energy expenditure rate that is either equal to or above the maximum energy expenditure rate of the tasks results in decreased work productivity performance due to the onset of physical fatigue and a higher risks of work-related musculoskeletal disorders.

Muscle activity, time to fatigue, and maximum task duration at different levels of production standard time.

[Purpose] This study investigated the variations in muscle fatigue, time to fatigue, and maximum task duration at different levels of production standard time. [Methods] Twenty subjects performed repetitive tasks at three different levels of production standard time corresponding to “normal”, “hard” and “very hard”. Surface electromyography was used to measure the muscle activity. [Results] The results showed that muscle activity was significantly affected by the production standard time level. Muscle activity increased twice in percentage as the production standard time shifted from hard to very hard (6.9% vs. 12.9%). The muscle activity increased over time, indicating muscle fatigue. The muscle fatigue rate increased for the harder production standard time (Hard: 0.105; Very hard: 0.115), which indicated the associated higher risk of work-related musculoskeletal disorders. Muscle fatigue was also found to occur earlier for hard and very hard production standard times. [Conclusion] It is recommended that the maximum task duration should not exceed 5.6, 2.9, and 2.2 hours for normal, hard, and very hard production standard times, respectively, in order to maintain work performance and minimize the risk of work-related musculoskeletal disorders.

A Conceptual Model of Work Productivity Associated with Work-Related Musculoskeletal Disorders in the Industrial Repetitive Task

The performance of workers is a very important factor that could affect the overall productivity result. In the industrial repetitive task, the performance of direct workers has a significant impact on the work productivity. In this kind of task, the work productivity loss is not only seen from time loss but also due to functional incapacity of the workers. The workers are present at work but functionally limited due to work-related musculoskeletal disorders (WMSDs). There are various studies which have reported on the effects of WMSDs on the work productivity, but few attempts have been made to investigate the relationship. This study aims to develop a conceptual model of work productivity associated with WMSDs as an aid to identify the relationship between the risks of WMSDs and the work productivity. The knowledge on the relationship is important to reduce the risk of WMSDs and at the same time can optimize the work productivity. A conceptual model of work productivity associated with WMSDs in the industrial repetitive task was developed based on the review on the existing models and theories. The factors involved in the model were discussed. The factors involved were work-related physical risk factors, muscle fatigue, work-related musculoskeletal disorders and work productivity.

Upper limb and lower back muscle activity during prolonged sitting

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.

Lift Augmentation between Passive and Active Vortex Generator

This study was conducted to investigate the performance of passive and active vortex generator on the wing’s flap. The triangular shape of passive vortex generator (VG) was developed and attached on the wing’s flap leading edge while the plasma actuator performed as active vortex generator. The test was carried out experimentally using subsonic wind tunnel with 300 angles extended flap. Three different types of turbulent flow; with Reynolds number 1.5 x105, 2.0 x105, and 2.6x105 were used to study the aerodynamics forces of airfoil with plasma actuator OFF. All Reynolds number used were below 1x106. The result indicated that airfoil with plasma actuator produced higher lift coefficient 12% and lift-to-drag ratio 5% compared to airfoil with passive vortex generator. The overall result showed that airfoil with plasma actuator produced better lift forces compared to passive vortex generator.

Variation of Work Productivity Performance at Different Levels of Production Standard Time

This study investigated the variation of work productivity performance at different levels of production standard time. Twenty subjects performed repetitive tasks at three different levels of production standard time, corresponding to “normal, “hard” and “very hard”. The work productivity and perceived fatigue were recorded. Analysis of Variance (ANOVA) was performed on the data and the results indicated that work productivity and perceived fatigue were significantly affected by production standard time. The results indicated that there was a decrease in work productivity performance as the perceived fatigue increased. The reduction in work productivity performance is related to the functional incapacity of the workers whereby they are exposed to higher risk of WMSDs in harder production standard time.

Muscles activities at two different work area boundaries during sedentary work

The aim of this study is to investigate the effects on upper limb and lower back muscles activities at two different work area boundaries during sedentary work. 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 (EMG) 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 the upper limb and lower back muscles activities increased significantly when performing work at the far boundary work area. The muscle activity at the far boundary work area is averagely 17% greater than at the near boundary work area. The result of independent sample t-test showed that the gender effects found to be significant at the far boundary work area.