Physical demands at work are considered an important risk factor of several musculoskeletal disorders (MSD; see [1
] for a systematic review). Moreover, heavy physical work may be associated with level of work ability [2
]. Heavy physical work is a general term, encompassing both working at high levels of aerobic load relative to maximum oxygen uptake, handling of heavy objects, and performing tasks demanding sustained exertion at high levels of force. Hence, the term heavy physical work does not specify pathogenic factors to target for workplace interventions to prevent health problems.
Individual performance and production output depend on being able to sustain workload over a period of time, which depends on both individual capacity and type of tasks performed. Several authors have suggested guidelines for work-intensity and -duration to ensure safety, health, and productivity of employees [3
]. Åstrand and coworkers have pointed out that the physical workload should be determined with indirect calorimetry and that the oxygen uptake must be evaluated with regard to the capacity of the working muscles [5
]. A criterion for the limit of acceptable workload is the occurrence of a marked increase in heart rate (HR; >10 beats per minute) after a period of working at a steady state with constant HR [6
], a sign of physiological fatigue. Rodgers and co-workers proposed that a workload of one third of the individual’s maximum capacity should be the upper limit for an eight-hour workday [7
]. Others have described workload limits for physically demanding jobs through “maximal acceptable work time” (MAWT), a term referring to workloads that can be sustained by an individual in physiologically steady state without causing exhaustion or discomfort [8
Work in the construction industry is generally considered physically demanding and construction workers show high prevalence of musculoskeletal pain [9
]. Higher rates of disability, lowered physical function, and reduction in muscular strength have been found in occupations with high levels of physical demands [11
]. However, the majorities of studies of heavy physical work were based on subjective measurements of physical demands. The validity and reliability of these exposure measurements are questionable [14
]. Van der Molen and co-workers did measure cardiovascular demands objectively by HR and oxygen consumption in groups of construction workers during several work tasks [15
]. These studies had a limited number of participants (N
= 8, 10, and 15, respectively) and measured demands during one single period. Two recent studies have objectively measured cardiovascular load for more than one day within other occupations commonly considered as physically demanding, female hospital cleaners [18
] and an unspecified group of blue-collar workers [19
]. Still, within construction work there is a paucity of studies with objective measurements of cardiovascular load over several days. Therefore, there is a need for knowledge of physical workload based on objective measurement of cardiovascular load in employees performing heavy physical work in the construction sector.
It seems a paradox, that physical activity during leisure time is considered health-promoting and essential for maintaining and increasing physical capacity and work ability [20
], while physical demands at work may be harmful. One might expect that heavy physical work would produce positive training effects [23
]. However, negative or no training effects from a life-time of heavy work exposure have been reported [25
]. Differences in patterns of physical activity during work and leisure could be an important factor when explaining this phenomenon [27
]. Moreover, heavy physical work may be a risk factor for leisure time physical inactivity [28
]. Therefore, information on physical demands and activity patterns during both work and leisure is needed.
There is a linear relationship between HR and oxygen consumption during a bout of work or exercise [29
]. Hence, HR may be measured as a proxy of workload or work intensity or aerobic strain. Some previous recommendations of workload have related work duration to workload operationalized as % of maximum O2
) or % of maximum HR (HRmax
) for the individual. HRmax
depends on age and there are several formulas for calculating HRmax
]. One problem with the %HRmax
approach is the fact that resting HR (HRmin
) never is zero, hence the percentage of HRmax
does not represent load above the resting state. Furthermore, some physically fit individuals exhibit very low HRmin
, hence their range of HR-variation (HR reserve) is larger for a given age. The relative HR (RHR or % of HR reserve) takes HRmin
into account by subtracting HRmin
from the HR measured during work and from HRmax
In the present study we aimed to elucidate cardiovascular loads in construction workers during work and leisure by relative HR (RHR) from objective measures over several days. We further evaluated the level of cardiovascular load in relation to individual factors, work ability, MSDs and general health.
The results demonstrated cardiovascular load characteristics in male construction workers during work and leisure. Further, the association between RHR at work and the participants’ age and aerobic fitness level is highlighted. We did not find any significant associations between cardiovascular demands at work and work ability, musculoskeletal complaints or general perceived health.
For the group as a whole an average workday was characterized by most time spent in ranges below 20% RHR and less time in higher ranges. For an average workday of 8 h, approximately 5 h were below 20% RHR, while approximately 40 min were spent in ranges above 40% RHR. A limited proportion of the participants (10%) had a mean RHR above the recommended threshold of 33% RHR and for the whole group approximately 70 min were in load ranges above this level of cardiovascular load on an average workday. Carpenters, henchmen and bricklayers represented professions with the highest mean RHR. Compared to carpenters and bricklayers, henchmen did have more episodes of both continuous exertion and rest periods, indicating a somewhat different work pattern. Foremen and project leaders seemed to have less physical demands, with lowest levels of RHR, no continuous periods of exertion and highest number of rest periods. This reflects that different professions within construction will have different physical demands, which should be taken into consideration when evaluating the construction sector. The physical demands of construction supervisors (e.g., foremen and project leaders) have previously been very scarcely investigated [41
Previous studies investigating masons, bricklayers and plasterboard work (carpenter task) during a full workday have found mean RHR ranging from 21 to as high as 39% RHR, with factors as brick and plasterboard sizes as important load varying factors [15
]. From our data the three professions found to have the highest cardiovascular demands (carpenter, bricklayer and henchman) exhibited HRs in the lower part of this range. However, the above-mentioned studies measured cardiovascular loads for one workday only. We found that the recorded HRs were significantly higher during the first day of measurement compared to following workdays (Koch et al.
work in progress). This finding indicates that work behavior may be altered the on first day of measurement. Still, compared to the general working life [42
], construction workers exhibit a higher level of cardiovascular load.
The mean MAWT for this sample was 14 hours, and a mismatch between length of workday and MAWT were found in approximately 1 in 5 individuals. A mean RHR of 24.4% would represent MAWT equal to the average workday of 8.1 h. Thus, all professions were within these limits. With this said, the distribution within RHR ranges and exertion/rest periods does imply that construction work is not a physiologically steady-state situation, but is rather fluctuating between levels of cardiovascular load. Therefore, this kind of work may not fulfil the assumptions behind the MAWT-equation, which is set pace ergometer cycling [8
]. Additionally, we may expect load carrying tasks to need additional predicting factors [43
]. Hence, there is a need for new approaches to estimate workload limits in physical occupations.
was significantly associated with RHR during work. Increasing age was associated with reduced cardiovascular load, indicating that younger workers had higher cardiovascular loads during work, compared to older workers. Similarly, Gupta and colleagues found seniority to be significantly more prevalent in workers with low RHR during work, compared to those with high RHR [19
]. Possibly, higher seniority workers allocate the more physically demanding tasks to younger workers. Alternatively, inexperienced workers perform tasks at a higher physiological cost than more experienced workers [7
]. It is possible that the senior workers are a selection of more fit individuals orthat senior workers are relocated to less physically demanding professions within construction. However, as found in the general population,
decreased significantly with age in our sample (results not shown), and there were no significant age difference between professions measured.
O2max was significantly associated with RHR during work. An increase in aerobic fitness will result in work being less physically demanding, with lower RHR as long as the level of physical demands remains unchanged. Even though there are differences in physical demands between professions, the relative demands for each person will be individually determined by level of fitness. We recorded large individual differences in the relative physical demands within the same profession.
There is an ongoing discussion concerning the paradoxical effect of physical exercise: seemingly negative effects of high physical activity at work and the health-improving effects of physical activity in leisure time [44
]. Our study shows that few individuals had continuous periods with RHR above one-third of their capacity and very few minutes were spent above 60% RHR during the workday. Intensive bursts of exhausting physical activity are needed to achieve a training effect on the cardiovascular system [46
]. Thus, the combination of duration and intensity seen in construction work do not meet levels required to achieve training effects. For the 10% of our cohort having a mean RHR above one third of maximal capacity, the demands may possibly have a negative effect, rather than a training effect [47
]. Foremen and project managers had the lowest amount of minutes above 33% RHR during work, the highest amount of minutes above 33% RHR during leisure and were the only professions spending more minutes in high ranges of RHR during leisure than during work. Generally, the present measurements indicated that cardiovascular load in spare-time was low. This may indicate the suggestion that occupations with manual work might have low levels of leisure time physical activity [28
Construction work has been associated to development of MSDs and reduction in work ability, and heavy physical work commonly is considered a major risk factor [1
]. Our data did not show any significant increase on musculoskeletal complaints or decrease in reported work ability with increasing cardiovascular demands. If musculoskeletal complaints develop over time, and RHR declines with increasing age, this combination could cancel out any possible association. Follow-up investigations of outcome based on these initial objective measurements, may provide more information concerning this issue. Reduction in work ability with high physical demands has also been shown in cross-sectional studies [2
]. A recent cross-sectional investigation on cardiovascular load and work ability found that high physical workload was associated with self-reported work ability in women, but not in men [19
]. Similarly, Karlqvist et al.
found that women needing to exceed their physical demands regularly during work had reduced general health and increased level of musculoskeletal complaints, however, men had no such problems [42
]. Thus, there may also be sex differences that we did not explore here.
The methods and design used in this study were chosen to provide a thorough objective description of the cardiovascular demands in construction work. The continuous measurement over several days provide a more solid foundation when describing general demands compared to studies with task or short period measurements, which may serve other purposes.
The formula for HRmax
presented by Tanaka and coworkers [30
] produced a standard deviation ~10 bpm for individuals of any age. Hence, the calculation of RHR can only give an approximate measure of cardiovascular load. Since arousal-inducing psychological factors may introduce large errors in measuring HR during rest and moderate levels of physical workload, obtaining valid measurements of HRmin
is difficult at the workplace. Therefore, we based HRmin
on the sex- and age-adjusted population means. The study participants were drawn from a variety of occupational titles within construction and will thereby give a good overall description of this work sector. However, they were male employees at Norwegian large-scale enterprises and data may not be generalized small enterprises and builders of private homes. In addition, there is possibility of selection bias of participants. From the 579 invited, 255 answered the questionnaire, 161 volunteered for technical measurement, and a sample of 57 were selected. Still, the participants monitored in the present study did not differ from the questionnaire group in any variable investigated, except smoking and gender. Concerning gender, there were only 18 females in total answering the questionnaire, hence females were weakly represented. However, at present this is the normal gender distribution in the construction sector. Long-term follow-ups are needed to determine the long term health effects of cardiovascular load during work.