[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.
[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.
Entities:
Keywords:
Energy expenditure rate; Work productivity; Work-related musculoskeletal disorders
The current trend in industrial tasks is moving towards more time-intensive production with
standardized, short cycle times1) and
limited completion times2) since an aim of
the manufacturing industry is to attain high work productivity. Process standard times, such
as the work pace or duty cycle time for a particular task, are determined by a process
engineer based on task time analysis. However, because workers must work in their designated
work locations and must adhere to predetermined task times3), their capacities and productivity state are often
overestimated.High work productivity is typically associated with hard production standard times. Hard
production standards generally produce high work productivity compared with low or no
production standards4). In general, tasks
become more repetitive in the case of harder production standard times and may expose
workers to a higher risk of work-related musculoskeletal disorders (WMSDs). WMSDs complaints
are frequently observed among workers involved in repetitive tasks5, 6). The capability of
workers performing repetitive tasks and the risk of WMSDs can be assessed by energy
expenditure measurement7). Energy
expenditure is a physiological measurement used to assess the influence of physical fatigue
on work performance among industrial workers7, 8).Energy expenditure is increased when tasks are carried out beyond a worker’s
limitations9). Hence, estimation of
energy expenditure is important indeed, as it serves as a reference in design of tasks that
will not induce fatigue and WMSDs among workers. The ability to accurately track energy
expenditure (EE) would be beneficial in the prevention of WMSDs7, 10). Energy
expenditure rate may vary according to the levels of production standard time assigned to
workers. Therefore, the objective of this study was to investigate the effects of energy
expenditure rate on work productivity performance at different levels of production standard
time in order to identify the maximum capability of the workers. This data could be used to
help ensure that tasks assigned to workers will not induce fatigue and to minimize the risk
of WMSDs.
SUBJECTS AND METHODS
A total of 20 subjects, 10 male and 10 female industrial workers, were recruited for a
series of experimental tasks. The subjects were between the ages of 22 and 45 years old
(30.9±7.711). They were first briefed on the experimental task process flow and equipment to
be used prior to performing the series of experimental tasks. Each subject was given an
information sheet outlining their involvement in the study and its potential risks. The
study was approved by the local ethics committee. Written informed consent was obtained from
each subject to ensure that they fully agreed to participate in the study. An Actiheart
monitoring device was placed on the chest of the subjects. The subjects were then instructed
to adopt a comfortable sitting posture with the sitting height adjusted individually to
obtain a knee angle of 90°. The working height was standardized by placing the work table’s
surface 5 cm below the position of the wrist when the elbow was flexed at 90°11). The subjects were required to perform the
experimental tasks after familiarizing themselves with them for 30 minutes. The tasks
involved repetitive assembly actions similar to an actual industrial assembly task. The
subjects were given two types of component, plastic clips and plastic foam rings. These
components were placed into a polybox and plastic container, respectively. The subjects were
instructed to connect the foam rings to the plastic clips using a jig, which pushed the foam
rings onto the clips. The subjects performed the tasks according to the production standard
times assigned to them. The production standard times used in the experimental tasks were
100% normal standard time (PSN-normal), 126% normal standard time (PSH-hard), and 140%
normal standard time (PSVH-very hard). The normal standard time was determined from a
Methods-Time Measurement (MTM) analysis. Heart rate and energy expenditure rate were
recorded using the Actiheart monitoring device, and work productivity of the subjects was
recorded for every 30 minutes.
RESULTS
Work productivity data were recorded in terms of quantity per hour and the percentage of
normal standard time achieved. The results for work productivity at different levels of
production standard time are summarized in Table
1.
Table 1.
Work productivity at different levels of production standard time
Production Standard (PS)
Work Productivity Target
Work Productivity (Quantity/Hour)
Percentage of Normal Standard (%)
PSN
100%
851
118.0
PSH
126%
890
123.0
PSVH
140%
928
129.0
The very hard production standard time resulted in the highest output, followed by the hard
production standard time and the normal production standard time. Work productivity data
were then analyzed to investigate the effect of production standard times on work
productivity. Repeated measures ANOVA was carried out for this purpose, and the results
revealed that production standard time had a significant effect on work productivity (Wilk’s
Lambda = 0.257, F (2, 18) = 2.8, p < 0.001, multivariate partial eta squared = 0.743). It
is evident that the average work productivity differed significantly among the three
production standard times (work productivity targets).The means and standard deviations of energy expenditure and heart rate are summarized in
Table 2.
Table 2.
Mean and standard deviation for energy expenditure (kcal/min) and heart rate
(BPM) at different levels of production standard time
Production standard time
Energy expenditure
Heart rate
Mean
Standard deviation
Mean
Standard deviation
PSN
1.03
0.05
89.8
3.05
PSH
1.19
0.14
96.7
4.69
PSVH
1.36
0.59
102.4
5.75
It can be observed that the workers’ energy expenditure and heart rate were higher for
harder production standard times. Repeated measures ANOVA analysis revealed that the energy
expenditure increased significantly as the production standard time became harder (Wilk’s
Lambda = 0.06, F (3, 17) = 89.036, p < 0.005, multivariate partial eta squared = 0.940).
The energy expenditure rate for the hard production standard time was higher than that for
the normal production standard time, with the percentage difference being 15.5%. The
assignment of a very hard production standard time resulted in an increase in energy
expenditure relative to the normal and hard production standard times, with the percentage
increases being 32.5% and 14.6%, respectively.
DISCUSSION
The results showed that work productivity increases significantly as the production
standard time becomes harder. This indicates that the workers were able to achieve higher
work productivity in the case of harder production standard times compared with the normal
production standard time. This observation agrees well with the findings of Shikdar and
Das12), who showed that work
productivity increases in the case of harder production standard times. The work
productivity target is attainable with the normal production standard time, but this is not
the case for the hard and very hard production standard times. The work productivity target
for the hard production standard time was 126% of the normal standard time. The results
showed that the workers were only able to achieve 123% of the normal standard time.
Similarly, the work productivity target for the very hard production standard time was 140%
of the normal standard time, and it was found that the workers were only able to achieve
129% of the normal standard time. There is an increase in job requirement in the case of
harder production standard times. In general, workers perform more repetitions of tasks in
the case of harder production standard times and are exposed to a higher risk of WMSDs. The
results agreed well with the results of previous studies, which also reported an association
between the risk of contracting WMSDs with higher repetition of tasks13, 14) and increases
in job requirement15). The results
indicated that workers tend to slow down in the case of harder production standard times due
to WMSD risks. The results are consistent with the findings of previous studies, which
showed that workers tend to slow down when they are fatigued due to WMSDs16). The findings concerning work productivity
can be attributed to the variations in energy expenditure rate at different levels of
production standard time. The energy expenditure rate for an activity was found to increase
significantly as the production standard time becomes harder. This agrees with the findings
of Li et al.7), who revealed that energy
expenditure increases when the frequency of tasks increases. 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%). The results also revealed that the average energy expenditure
rates for an activity in the case of the normal (1.03 kcal/min) and hard production standard
times (1.19 kcal/min) were less than the maximum value, 1.2 kcal/min, for light repetitive
tasks involving both arms in a previous study17). The energy expenditure value reported by Garg et al.17) is used as a reference because it serves
as a reliable benchmark in estimating energy expenditure7, 18). In contrast, the average
activity energy expenditure rate obtained in the case of the very hard production standard
time (1.36 kcal/min) exceeded the reference value, which suggested that the workers were
exposed to a higher risk of WMSDs.The heart rate of the workers was also found to be higher in the case of a harder
production standard time, and the energy expenditure rate increased with the increment in
heart rate. These results agreed well with the findings of a previous study that discovered
a linear relationship between energy expenditure, heart rate, and oxygen uptake19). The dynamic muscle exertions during
repetitive tasks require oxygen, and the metabolic demands of the muscles increase as
activity increases. Therefore, consumption of oxygen will increase in conjunction with an
increase in heart rate in order to circulate more blood, which will carry oxygen to the
working muscles. The results of this study indicated that workers are exposed to a higher
risk of WMSDs when carrying out tasks with a very hard production standard time. This is
because the energy expenditure rate exceeds the maximum capability of workers when working
with a very hard production standard time. The results are supported by the findings of
previous studies that emphasized the need to accurately track the energy expenditure rate of
workers in order to prevent WMSDs7, 10). In conclusion, working with an energy
expenditure rate that is either equal to or above the maximum energy expenditure rate of the
tasks will decrease work productivity performance due to the onset of physical fatigue and
increase the risk of WMSDs. Therefore, it is important to identify the maximum energy
expenditure rate to ensure that the tasks assigned will not result in excessive fatigue in
workers, which would lead to a risk of WMSDs and a reduction in work productivity
performance.