Introduction
Physical fitness is an important marker of health in adults (Bouchard et al.
2012; Sjøgaard et al.
2016). For instance, higher levels of physical fitness as indicated by upper- and lower-body strength are associated with a lower risk of all-cause mortality in adults, irrespective of age (García-Hermoso et al.
2018). Further, gains in physical fitness (i.e., balance, lower limb muscle strength) following 8 weeks of combined balance and strength training improved gait performance (i.e., habitual gait speed) in middle-aged workers (Granacher et al.
2011b). Additionally, components of physical fitness are related to psycho-cognitive performances (e.g., short-term memory, stress resilience) (Cassilhas et al.
2007; Liu-Ambrose et al.
2010; Forcier et al.
2006; Tonello et al.
2014). A meta-analysis examined associations between measures of cardiorespiratory fitness (CRF) and cardiovascular reactivity to psychological stressors in adults (Forcier et al.
2006). Individuals with higher levels of CRF revealed lower values of heart rate reactivity as a physiological measure of acute psychological stress (Forcier et al.
2006). Moreover, a longitudinal study examined the effects of a 24-week resistance training program on cognitive performances (e.g., short-term memory, attention) in sedentary old adults and found significant gains in maximum strength (e.g., chest press, leg press), together with improved short-term and long-term memory, as well as attention (Cassilhas et al.
2007). Consequently, gains in physical fitness can be translated to improvements in psycho-cognitive performances.
In the working population, physical fitness as well as psycho-cognitive performances can be affected by physical demands at work (Holtermann et al.
2010; Savinainen et al.
2004; Torgén et al.
1999; Then et al.
2014). More specifically, physical work demands such as peak loadings, repetitive and fatiguing movements, or constrained postures may induce muscle pain and compromise musculoskeletal function, as well as mental health (Sjøgaard et al.
2016; Søgaard and Sjøgaard
2017). In fact, Savinainen et al. (
2004) examined the effects of physical work demands as indicated by ratings of perceived exertion (RPE, scale 6–20) during a working day. Among middle-aged Finnish municipal workers, components of physical fitness (e.g., muscle strength, CRF) were associated with higher levels of muscle strength (e.g., maximum trunk extensor and handgrip strength) in workers with low (RPE ≤ 12.8 and 12.5 in males and females, respectively) compared with high physical workloads (RPE > 12.8 and 12.5 in males and females, respectively). Further, better outcomes of cognitive performance (e.g., short-term memory, semantic memory) were observed in middle-aged and old workers with high versus low mental work demands (Then et al.
2014). Moreover, middle-aged workers in less physically demanding jobs (i.e., white-collar workers) experienced more mental stress at the worksite compared with workers who experienced high physical work demands (i.e., blue-collar workers) (Wu and Porell
2000). Thus, workers with primarily mental work demands can have higher levels of physical fitness (e.g., muscle strength), cognitive performance (e.g., short-term memory), and perceived psychological stress compared with workers with physical work demands.
With respect to higher levels of physical fitness, cognitive performance, and psychological stress in mental compared to physical work demands, associations between measures of physical fitness and psycho-cognitive performance may be more pronounced in workers with mental work demands. However, it is unresolved if measures of physical fitness (e.g., CRF, muscle strength, balance) and psycho-cognitive performances (i.e., short-term memory, perceived stress, work ability), as well as their relationships, are different in young and middle-aged workers with physical versus mental work demands. A better understanding on physical and psycho-cognitive performance measures in workers with primarily physical versus mental work demands may help to promote exercise training programs for employees with specific work demands (Søgaard and Sjøgaard
2017). The purpose of this study was to examine measures of physical fitness and psycho-cognitive performances in the young and middle-aged workforce with primarily physical versus mental work demands. In addition, we aimed to assess the associations between the measures of physical fitness and psycho-cognitive performances. Based on the relevant literature (Savinainen et al.
2004; Søgaard and Sjøgaard
2017; Then et al.
2014; Wu and Porell
2000), we hypothesized greater fitness measures and better cognitive performances together with higher levels of perceived stress in workers with primarily mental compared with physical work demands. Further, we expected significant positive associations between variables of physical fitness and cognitive performances and significant negative associations between physical fitness and perceived stress (Forcier et al.
2006; Cassilhas et al.
2007), particularly in workers with primarily mental work demands.
Discussion
The main findings of this research were that: (i) MD showed better performances in balance, trunk extensor muscular endurance, and cognitive function compared with PD, particularly in individuals with low LTPA levels; (ii) perceived stress was lower in MD compared with PD; (iii) small-to-medium sized associations between physical fitness and psycho-cognitive performance measures in the workforce were more pronounced in MD.
One important finding of our cross-sectional study revealed that work demands affected components of physical fitness (i.e., balance, trunk extensor muscular endurance) in young and middle-aged employees. In fact, trunk extensor muscular endurance and static balance were better in MD compared with PD. More specifically, trunk muscle endurance was higher in MD with low LTPA compared with PD with low LTPA. In individuals with higher levels of LTPA, no performance differences were observed between MD and PD. Our results are well in line with the findings of Savinainen et al. (
2004). These authors revealed that muscle strength (e.g., maximum trunk extensor and handgrip strength) was better in workers with low (i.e., MD) compared with high physical workloads. Accordingly, the authors concluded that high physical work demands do not necessarily translate to better physical fitness in the workforce (Savinainen et al.
2004). In contrast, it has even been postulated that high physical work demands in terms of intensities or repetitions may induce musculoskeletal dysfunction, pain, and/or adverse health events (Søgaard and Sjøgaard
2017). In this regard, it was demonstrated that PD workers have higher risks for long-term sickness absence and early mortality, particularly in men (Holtermann et al.
2012; Coenen et al.
2018). From this, it follows that, in our study, employees with pronounced physical work demands could have compromised physical fitness (i.e., trunk muscle endurance, static balance). This is of particular interest because lower levels of trunk muscle endurance and static balance are associated with an increased risk of sustaining low back pain and/or falls (Biering-Sørensen
1984; Granacher et al.
2011a,
2013). Future longitudinal studies may examine whether physical versus mental work demands adversely affect physical fitness and/or health in young and middle-aged adults. It seems as if physical activity can have positive and negative effects on performance and markers of health, depending on the setting of physical activity behavior. If it is conducted during leisure time, it has beneficial effects on musculoskeletal function and health (Sjøgaard et al.
2016; Søgaard and Sjøgaard
2017; Holtermann et al.
2010,
2012). For instance, Holtermann et al. (
2012) showed that higher levels of LTPA had a positive effect on long-term sickness absence. Our subgroup analyses revealed differences between MD and PD in trunk muscle endurance for individuals with low but not high LTPA. In other words, LTPA modified the effects of physical work demands on physical fitness (i.e., trunk muscle endurance). Interestingly, higher levels of physical fitness can contribute to daily activities, occupational performance, and health (Bouchard et al.
2012; Sjøgaard et al.
2016). In terms of occupational performance, associations between changes in physical fitness (e.g., trunk flexor/extensor strength) and on-the-job performance (i.e., sickness presenteeism) were examined following 3 months of a multifactorial intervention program (e.g., strength training, cognitive behavioral training) in healthcare workers (Christensen et al.
2015). Medium-sized correlations were reported between increments in trunk flexor/extensor strength and gains in on-the-job performance (0.411 ≤ Pearson’s
r ≤ 0.456), indicating the importance of physical fitness (e.g., trunk muscle strength) for occupational performance (Christensen et al.
2015).
A second finding showed that physical work demands affected cognitive performance and perceived stress in the young and middle-aged workforce. More precisely, cognitive performance was higher and perceived stress was lower in MD compared with PD. This was particularly pronounced in individuals with low LTPA levels. Recently, Then et al. (
2014) examined the effects of mental work demands on cognitive performance (i.e., Trail Making Test, verbal fluency test) in adults aged 40 to 80 years. In accordance with our results, the authors reported better cognitive performances in MD compared with PD. It was suggested that particularly high mental work demands may provide optimal stimuli to improve cognitive performances (Then et al.
2014). In fact, it has previously been shown that high mental demands are essential to induce cognitive learning (Fairclough et al.
2005). In this study, MD performed better in the cognitive task (i.e., digit symbol substitution test) than PD. This might be due to the fact that MD experienced high mental work demands. Of note, our findings in regards of lower stress levels in MD compared with PD are in contrast with the literature. Myrtek et al. (
1999) showed that white-collar workers (i.e., workers with primarily mental work demands) were more likely to experience mental stress at work compared with blue-collar workers (i.e., workers with primarily physical work demands). This discrepancy in findings can be explained by different LTPA levels in the study of Myrtek et al. (
1999) as compared with our study. While we found higher LTPA levels in MD compared with PD, Myrtek et al. (
1999) reported similar LTPA levels in white- and blue-collar workers. Interestingly, there is evidence that more active individuals seem to be more resilient to psychosocial stressors (Tonello et al.
2014; Teisala et al.
2014). Moreover, a meta-analysis showed that individuals with higher levels of physical fitness revealed lower levels of perceived stress (Forcier et al.
2006). We found better trunk extensor muscular endurance and static balance in MD compared with PD. Thus, it can be hypothesized that, in our study, better stress resilience in MD versus PD could be related to higher LTPA and/or fitness.
Another important finding of our study was the small-to-medium sized associations between physical fitness and psycho-cognitive performances (− 0.279 ≤
ρ ≤ 0.434), particularly in MD. These results are well in line with the literature. For instance, Teisala et al. (
2014) reported medium-sized correlations between CRF (VO
2max) and perceived stress in healthy males with a mean age of 34 years. Moreover, Newson and Kemps (
2008) showed better cognitive performances (e.g., attention, working memory, processing speed) in adults (mean age 46 years) with high-level compared with low-level CRF (VO
2max). The findings from our cross-sectional study and the literature indicate that individuals with better fitness levels also show better psycho-cognitive performances (i.e., attention, short-term memory, perceived stress, work ability), particularly in individuals with predominantly mental work demands. Nevertheless, future studies should examine whether physical exercise programs with the goal to improve physical fitness have the potential to induce enhancements in psycho-cognitive performances in MD and PD workers.
Strengths and limitations of the study
A strength of this study is that it is the first to examine physical fitness and psycho-cognitive performances as well as their associations in healthy, young and middle-aged MD versus PD workers. The data collection was undertaken by the same experienced exercise scientists and/or physiotherapists to avoid inter-observer variations. Additionally, the tests used are established and reliable tools for assessing physical fitness and psycho-cognitive performances in the field (Frey et al.
1999; Burnstein et al.
2011; Suni et al.
2014; Tschopp et al.
2001; Latimer et al.
1999; Wolinsky et al.
2005; Hinton-Bayre and Geffen
2005; Cohen et al.
1983; Silva Junior et al.
2013). Lastly, the magnitude of several fitness and psycho-cognitive outcomes such as handgrip strength, jump-and-reach performance, or perceived stress are similar to those previously observed in young and middle-aged adults in Germany, Finland, and Denmark (Suni et al.
2014; Tittlbach et al.
2005; Jay et al.
2015).
We have to acknowledge a few limitations of this study. First, the present study used a cross-sectional study design. This design is the best way to determine prevalence and allows for assessing multiple outcomes (Mann
2003). Although cross-sectional studies are used to infer causation, they do not allow for cause-and-effect relations (Mann
2003). Second, factors such as lifestyle, socioeconomic status, and/or education could have affected physical fitness and/or psycho-cognitive performances. However, socioeconomic status is a latent construct relying on different indicators, thereby limiting data interpretation (Fliesser et al.
2018). Interestingly, studies indicated that different levels of socioeconomic status, education, and/or lifestyle are not or even adversely related with different fitness measures (Strand et al.
2011; Jensen et al.
2017; Koster et al.
2006). For instance, neither education nor occupation had an effect on grip strength in middle-aged men and women (Strand et al.
2011). Further, social class as operationalized by the level of education and job profile did not affect CRF (i.e., estimated VO
2max) in a large sample of middle-aged, employed men (Jensen et al.
2017). Most importantly, effects of socioeconomic status as operationalized by the level of education and income on physical function in middle-aged men and women were predominantly explained by body mass index and LTPA (Koster et al.
2006). In the present study, body mass index as well as LTPA were assessed, thereby controlling indirectly for socioeconomic status. Nevertheless, future studies need to systematically include covariates such as socioeconomic status, education, or lifestyle. Third, we cannot rule out a selection bias during the recruitment process. In other words, workers with better performance measures could have been more likely to participate than workers with lower performance measures.
Practical implications
Recent review articles suggested to regularly include physical exercises into the daily routines at the workplace to counteract the negative side effects of occupational tasks (Sjøgaard et al.
2016; Søgaard and Sjøgaard
2017). In fact, given that most adults spend half of their waking hours at the workplace, the worksite setting offers a unique opportunity to promote physical activity and fitness. With respect to the present cross-sectional findings, physical activity in the form of physical exercises should be increased to maintain or develop physical fitness and counteract the negative side effects of physical work demands. In particular, the correlation analysis indicated that gains in physical fitness may at least partly translate to benefits in psycho-cognitive performances and/or vice versa. Thus, physical exercises with the goal to improve physical fitness measures in the workforce could improve psycho-cognitive performances as well. Future studies should examine whether physical exercises can differently affect changes in physical fitness and psycho-cognitive performances in MD versus PD workers. These findings are essential before implementing work demand-specific public health promotion programs in the wider population.
Conclusions
Workers with primarily mental compared with physical work demands exhibit better balance, trunk extensor muscular endurance, and cognitive performance, as well as lower levels of perceived stress. Leisure-time physical activity (LTPA) modified the effects of physical work demands on physical fitness (i.e., trunk muscle endurance) and cognitive performance (i.e., digit symbol substitution test). Further, small-to-medium sized associations were found between physical fitness and psycho-cognitive performances, which indicates that gains in physical fitness may at least partly contribute to psycho-cognitive performance and/or vice versa, particularly in MD workers. Based on our findings, future longitudinal studies should examine the effects of physical versus mental demands at work on physical fitness and psycho-cognitive performance in young and middle-aged adults. Additionally, future research should look at cohort-specific (MD vs PD) effects of physical exercise programs on physical fitness and psycho-cognitive performances.
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