Work capacity assessment of Nigerian bricklayers

Article history: Received March 7, 2011 Received in Revised form August, 25, 2011 Accepted 25 August 2011 Available online 28 August 2011 The main aim of this study is to assess the physical work capacity of bricklayers with focus on the energy expenditure during work. Eighty Nine bricklayers’ working on various sites in Ibadan and Eruwa towns of Oyo State, Nigeria are used for the study. Correlation and regression analysis using SPSS 16.0 Statistical Package was used to determine the relationship between VO2 given the age and weight of the subjects; % RHR(Relative Heart Rate) and working heart rate (HRW) given weight; VO2 and %RHR given Body Mass Index (BMI). The results showed that the mean energy expenditure of bricklaying was 1.5l/min of oxygen (7.23Kcal/min, using a conversion factor of 4.82) which classified bricklaying as “heavy work”. A rest allowance of 64.45% (38.67 minutes rest for 60 minutes work duration) was calculated . It was concluded that there is a need to redesign the work content of the aforementioned occupation in order to reduce excessive strain on the workers, which in turn will increase productivity. © 2012 Growing Science Ltd. All rights reserved.


Introduction
Working in the construction industry has been considered to have ergonomic problem due to the fact that it requires working above the shoulder and below the knee height (Schneider & Susi, 1994).Similarly, Samuelsson and Lundholm (2006) observed that the ergonomic problem in the construction industry could be as a result of heavy lifting, working on one side, and strenuous work postures.While, Larcher and Sohail (1999) noted that there are huge financial cost and human agonies associated with construction industry.Simonsson and Rwamamara (2007) observed that measuring the significance of work related accidents and personnel turnover in construction company may be difficult.The activities associated with construction industry were highlighted by Snook (1982) as a potential risk area.Despite the various hazards that the construction workers are exposed to, there has been very little attention towards the health and safety of these workers (Koningsveld & Van Der Molen, 1997).
In developing countries like Nigeria, labour cost is cheap and most work in the construction industries are done manually.In such countries the physical demands of the task often exceed the physical capabilities of the worker (Scott & Charteris, 2004).In fact, Sluiter and Frings-Dresen (2007) noted that for a type of work to be compatible with the worker and to enhance productivity, the health status, physical capabilities, absence of sickness, absence of accidents and task performance are essential.Physical tests have been used by organizations to assess the capability of workers for physically demanding jobs as in military formations (Blizon, 2002).As a result of this fact, many ways have been adopted in measuring workers , responses to manual tasks in order to appraise the incompatibility, and to evaluate the effectiveness of intervention strategies.In order to match a person's work capacity with the requirements of his/her job, there is a need to know the individual's energy capacity and how much the job demands from this capacity.The energy requirements of a given task are determined by allowing a "standard" person to perform the task and again measure the person's reactions to the task.However, Kroemer et al. (2000) recommended the measurement of reaction of workers since "standard" people are usually not available.The heart rate is commonly used to estimate the energy expenditure or physical strain during sports, work or daily activities (Bot & Hollander, 2000;McArdle et al., 2001).This indirect method is based on a linear relationship between heart rate (HR) and oxygen uptake (VO 2 ) during steady state conditions and gives the opportunity of an easy and relatively inexpensive determination of the VO 2 (Scott & Christie, 2004;McArdle et al., 2001;Bot et al., 2000;Haskell et al., 1992;Strath et al., 2004).Stifelman (2007) discussed techniques to measure human energy expenditure in bricklayers.Similarly, Oke et al. (2008) developed a framework for energy expenditure for bricklayer under different postures to provide information on the type of posture to be adopted for bricklaying and estimating the energy required at such postures.However, the methodology provided may only be used in the laboratory setting.Therefore, the study of the work capacity or energy expenditure of bricklayers is still an interesting area of research especially for Nigerian bricklayers.The nonavailability of oxygen measuring equipment and the fact that its use may interfere with the work of the bricklayers allowed for the methodology adopted by Scott and Christie (2004) and others (McArdle et al., 2001;Bot et al., 2000;Haskell et al., 1992;Strath et al., 2004) to determine the energy expenditure, physiological response and aerobic strain of bricklayers including margin of safety on field.

Material and methods
The field study was conducted at building sites in Ibadan and Eruwa in Oyo state of Nigeria.89 (Eighty Nine) Bricklayers working on different building sites participated in the study.The heart rates (HR) of each worker were measured with the use of a digital sphygmomanometer (POLYGON YS796).The resting heart rate was measured by asking the subject to sit down quietly for five minutes and then measuring the resultant heart rate.Working heart rate was measured while the bricklayers were working over a one hour period that did not include breaks.Weights of the workers were also recorded with weighing machine (HARSON H89DK) before the start of work.The measurements of the weights were to the nearest 0.1 kg and the subjects were on the machine with bare foot, light clothing and stayed for between one and two minutes.Moreover, the heights of the workers were measured using a locally fabricated Standiometer.VO 2 of each participant was determined form the HR values obtained during the experiment using the linear regression model developed by Scott and Christie (2004) as: Y = 0.259X -6.422,where Y = predicted oxygen consumption in ml.kg -1 min -1 , X = measured heart rate in beats min -1 ; VO 2max was also determined by using Astrand -Astrand nomogram as modified by Tayyari and Smith (2003) as: For women: VO 2max = AG.(131.5.VO 2 ) ÷ (HR -72), (2) where AG = 1.12 -0 .0073age.
The energy expenditure of bricklayers was determined and relationships between weight and VO 2; weight and VO 2max ; age and VO 2; age and VO 2max ; heart rates and VO 2; heart rates and VO 2max were established using Paired samples t-test as available in SPSS 16.0 Statistical package.
The RHR which is also an indicator of physical workload that is related to muscular activities as reported by Wu and Wang (2002) was calculated.% RHR was given as, where HR W = Average Working HR, HR r = Resting HR, HR MAX = Maximum HR, given as 220-age (Astrand & Rodahl, 1986).For manual activities rest allowance (RA) should be provided as compensation.The RA was calculated using the following equation adapted from Niebel and Freivalds (2003): where RA = Rest Allowance, as percentage that is added to Working Time (WT), and ∂HR = Working HR-Resting HR.

Results
The summary of the anthropometric characteristics and working heart rates in terms of percentiles, means and standard deviations are presented in Table 1.The mean height of the bricklayers that were studied was 1.6m while their mean age was 33.7 years.
The mean body mass index (BMI) which is a measure of obesity and defined as weight in kilograms divided by height in metres squared was 22.7 Kg/m 2 .The bricklayers expended an average of 1.5 l /min of oxygen (7.23Kcal/min, using a conversion factor of 4.82) whiles the calculated percentage relative heart rate (RHR) was 58.5% (SD 19.0%).The mean working heart rate was 120.8 bpm and the resting heart rate was 68.6 bpm.
BMI had a positive correlation with % RHR (r=0.220,P=0.038) and VO 2 (r=0.330,P= 0.002) but no correlation with both working heart rate (r=0.194,P=0.069) and VO 2max (r=0.090,P=0.400).The models which best describe the relationship between the variables, which have correlation were determined using the SPSS 16.0 Statistical Package.The % RHR can best be predicted using any of the following equations as they have the same R Square of 0.243 as shown in As shown in Table 6, the VO 2 can be predicted fairly given BMI, using the following equation:  There a weak association between the % RHR and BMI and as such the relationship may not be predicted fairly as shown in Table 7.The Rest Allowance (RA) was calculated to be 64.45%

Discussion
The bricklayers in this study expended an average of 1.5 l min -1 of oxygen and mean heart rate of 120.8bpm, which classified their work as "heavy work" using the classification of Kroemer et al. (2000).Kroemer et al. (2000) defined the heaviness of work as: Extremely heavy work: 50KJ (12.5Kcal) -160 beats per minute.The mean heart rate (120.8bpm) needed to do bricklaying work in the present study was above the recommended limit of 110 bpm for an 8-hour work shift (Sanders & McCormick, 1993;Saha et al., 1979).Maritz et al. (1961) had suggested an average working HR of 105 bpm for standard 8-hr industrial job with a range of 95-115 bpm.
The results of the present study differs from the work of Astrand (1967) which found a mean heart rate for 10 bricklayers as 97.9 bpm (SD 9.5 bpm).The difference in the two studies may as a result of the number of subjects involved as the present study used 89 bricklayers.
The mean % VO 2Max of 52% was more than the recommended 33% as recommended by the NIOSH Committee.The % RHR of 57.4% obtained from the study was higher than 30% recommended by Shimaoka et al. (1998) and 24.5% recommended by Wu and Wang (2002).The significance of these findings is that tasks performed can cause high cardiovascular load for an 8-h workday and subject the workers to fatigue and higher muscular strains.The resultant effect of this is associated muscular pain.Knight (1984)  for the fatigue due to physical strain.The required rest period was very high as compared to the actual rest time in the field as the bricklayers only rest while eating, drinking or waiting for materials and these are not done every hour.Therefore, cumulative muscular fatigue would set in and may lead to high risk of occupational health hazard conditions while working with a resultant pain after the day's job.

Conclusion
From the study on bricklayers, it was observed that physical work capacity depends on anthropometric characteristics of the bricklayers.With ageing, physical work capacity rapidly diminished even with increase in body weight.The work contents of the bricklayers are usually above the recommended value and could lead to physiological strain on the workers which may be overcome by redesigning the working system.
Thus, redesign of workplace and work method is urgently required to reduce the work stress factor.It is recommended that the field working conditions in Nigeria are very risky and accident-prone.The occupational health status of the workers associated with this highly demanding industry needs to be considered to reduce accidents and injuries on site.Lifting and motorized positioning devices should be provided in order to reduce the stress and energy expenditure involved in carrying loads.Manual workers should be tested and evaluated for their fitness for a particular task, and their working time should be optimized without discomfort, to harness maximum efficiency of the worker for the designated operation, which will increase the net output.
Table 2 shows the relationship between VO 2 and age.From the Table, the curve that best describes the relationship is S-Equation with the highest R Square of 0.108 (Table 2), which gives the relationship as: −, where Y= VO 2

Table 2
Relationship between VO 2 and Age (Dependent Variable: VO 2 , The independent variable is Age)

Table 3
Relationship between VO 2 and Weight (Dependent Variable: VO 2 , The independent variable is Weight)

Table 5
Relationship between working heart rate and weight (Dependent Variable: HR W , The independent variable is Weight)

Table 6
Relationship between VO 2 and BMI (Dependent Variable: VO 2 , the independent variable: BMI)

Table 7
Relationship between %RHR and BMI (Dependent Variable: %RHR, The independent variable is BMI) Niebel and Freivalds (2003)cation regarding whether subjects are underweight, normal, overweight or obese:The mean value of 22.7 Kg/m 2 obtained was midway in the normal range, suggesting that bricklayers may be towards the heavy-for-height end of the population with a proportion being overweight.The maximum BMI obtained was 33.1 Kg/m 2 and the minimum 17.0 Kg/m 2 .Using the adaptedNiebel and Freivalds (2003)equation, the rest time should be 64.45% while the work time should be 35.55%which means a rest time of 38.67 minutes within 60 minutes of work.This is necessary to compensate