Introduction
Psychosocial stress is a major health threat in modern society (Gerber & Schilling,
2018; Tomitaka et al.,
2019). As highlighted by the American Psychological Association (
2017), the occupational environment constitutes one of the most significant sources of stress. The process linking psychosocial stress to disease is considered to be highly complex and, to date, not fully understood (Cohen, Janicki-Deverts, & Miller,
2007). While long-term (up to years) stress is related to negative health outcomes (Elfering et al.,
2005), evidence suggests that this relationship can in part be explained by short-term (day-level) effects of stress on health behaviors (Chandola et al.,
2008; Slopen et al.,
2013; Sonnentag & Jelden,
2009). In this article, we explicitly address these possible short-term pathways of occupational stress, and their potential effects on one specific health behavior, namely physical activity (Fransson et al.,
2012; Kivimäki et al.,
2013; Kouvonen et al.,
2013).
The importance of physical activity for health is well acknowledged (Huang et al.,
2021a), whereby participation in regular physical activity is associated with improved health and decreased mortality (Ekelund, Dalene, Tarp, & Lee,
2020; Mora, Cook, Buring, Ridker, & Lee,
2007). Therefore, the World Health Organization recommends certain levels of moderate-to-vigorous physical activity (MVPA) per week (Bull et al.,
2020). Evidence further suggests that physical inactivity is positively related to a variety of diseases and higher risks for premature death (Huang et al.,
2021b). Research has also shown that personal awareness of these health effects is only a weak predictor of people’s intention to be (or to become) physically active and/or their actual physical activity behavior (Faries,
2016; Rhodes & Courneya,
2003). As introduced above, research has shown that psychosocial stress at work predicts lowered execution of healthy behaviors, such as physical activity (Chandola et al.,
2008). Consequently, the negative effects of psychosocial stress on health are presumed to be, at least partially, explained by changes in health behaviors, namely lowered levels of physical activity.
The resource model of self-control is one often used theoretical model to explain the relationship between increased psychosocial stress and changes in health behaviors (Baumeister, Heatherton, & Tice,
1994; Englert,
2016; Hagger, Wood, Stiff, & Chatzisarantis,
2010; Sax,
1997). Within this model, it is assumed that stress reduces the available resources for self-regulatory control, resulting in difficulties to maintain healthy behaviors (Baumeister, Vohs, & Tice,
2007). Prior investigations have shown that trait self-control is associated with higher engagement in physical activity independently of people’s stress levels (Kinnunen, Suihko, Hankonen, Absetz, & Jallinoja,
2012; Wills, Isasi, Mendoza, & Ainette,
2007). More importantly, research has also demonstrated that trait self-control facilitates maintenance of healthy behaviors (e.g., nonsmoking, healthy eating, physical activity) if people are exposed to stress (Crescioni et al.,
2011; de Ridder, Lensvelt-Mulders, Finkenauer, Stok, & Baumeister,
2012; Martin Ginis & Bray,
2010; Oaten & Cheng,
2006).
Most prior research has focused on the question whether physical activity (and high levels of cardiorespiratory fitness) has the potential to mitigate some of the deleterious health effects associated with high stress levels (Gerber, Börjesson, Ljung, Lindwall, & Jonsdottir,
2016; Gerber & Pühse,
2009; Gerber et al.,
2019; Klaperski,
2018; Park & Iacocca,
2014). Therefore, investigating the reciprocal effect of stress on PA as a health behavior is an important, yet understudied field of research (Gerber, Fuchs, & Pühse,
2013; Gerber et al.,
2015; Isoard-Gautheur, Ginoux, Gerber, & Sarrazin,
2019; Stults-Kolehmainen & Sinha,
2013). Moreover, modern technologies facilitate the assessment of stress in naturalistic environments beyond retrospective self-reports (Kasten & Fuchs,
2018). Ecological momentary assessment (EMA) is increasingly used in sport and exercise science (Reichert et al.,
2020). Herein, portable devices can assess multiple experiences in realistic contexts, and in almost real-time, rather than necessitating long-term recall (Reichert et al.,
2020; Stone & Shiffman,
1994). This is especially important in the assessment of affective–emotional processes, which have been shown to be strongly influenced by recall bias, e.g., by duration neglect (Fredrickson & Kahneman,
1993). Stress experiences are emotionally represented phenomena which further highlights the advantage of EMA in capturing experiences within the contexts they are actually situated in (Kasten & Fuchs,
2018; Reichert et al.,
2020). In the current study we applied EMA to assess stress in real-life and close to real-time in order to assess stress experiences within personally relevant contexts and with minimized recall bias (Reichert et al.,
2020). Applying the theoretical assumptions of the resource model of self-control, we expect that on a day with more stress at work, participants have to rely on self-control in order to engage in physical activity after completion of work.
An occupation which is particularly known for encountering several acute and chronic stressors is policing (Brown & Campbell,
1990; McCreary & Thompson,
2006). While police officers are acknowledged to start their career in very good health, some may develop severe health problems due to the cumulative impact of stress experienced during the course of their career (Waters & Ussery,
2007). Reports on stress-related health behaviors include smoking as well as alcohol consumption (McCarty, Aldirawi, Dewald, & Palacios,
2019). As stated by Buckingham, Morrissey, Williams, Price, and Harrison, (
2020), policing has become increasingly sedentary. In addition, a study by Ramey et al., (
2014) showed that police officers are more active on days off duty.
Research questions and hypothesis
The main purpose of the present study was to find out whether stress at work during the day influenced device-based measured levels of MVPA after work in police officers. We also examined whether this relationship was moderated by dispositional self-control. Based on the literature presented above (Fransson et al.,
2012), we hypothesized that individuals who experienced more stress during their working day would engage in less MVPA after work (Hypothesis 1). Moreover, we expected that this association would be moderated by participants’ dispositional self-control (Oaten & Cheng,
2006), in the sense that among individuals who experienced high levels of occupational stress, those who reported higher self-control would be more able to maintain their MVPA levels than their counterparts with low self-control (Hypothesis 2A). Among participants who experienced low occupational stress, we assumed that after-work MVPA levels would be similar among participants with low vs. high levels of dispositional self-control (Hypothesis 2B). These relationships are expected to be observable at interindividual level.
Discussion
We investigated the effects of acute stress at work on MVPA after work in consideration of dispositional self-control as a moderating variable. We hypothesized that with increased experiences of stress at work, individuals with higher levels of dispositional self-control would be more likely to maintain their levels of MVPA after work. However, this assumption was not confirmed in the present sample of police officers. Thus, the level of stress at work did not significantly predict the level of MVPA after work, regardless of the level of dispositional self-control.
This finding is to some extent at odds with previous evidence. Sonnentag and Jelden (
2009) showed that police officers’ situational constraints were in fact negatively related to self-regulatory resources and physical activity after work. However, role ambiguity and time pressure as different types of stressors did not show similar effects. Consequently, different stressors may antecede different effects on self-regulatory measures as well as health behaviors. These effects could be explained by different stress regulatory pathways in the brain (Maier, Makwana, & Hare,
2015). However, evidence regarding interaction effects of stress and dispositional self-control on subsequent physical activity is scarce. Some studies on the more general effects of psychosocial stress on subsequent physical activity indicate possible gender effects. A study with police officers by Ramey et al. (
2014) presented evidence that the association of psychosocial stress at work and subsequent physical activity was not direct but moderated by gender. However, we did not find significant effects based on gender in the present sample. In a sample of college-aged women, Lutz, Stults-Kolehmainen, and Bartholomew (
2010) showed that sports participation under stress was predicted by stages of change. During the examination period, participants in the maintenance stage exercised more, while other stages showed the opposite or no associations. The explanation presented by Lutz et al. (
2010) was that consistent exercisers invested self-regulatory efforts in executing the health behavior over a long period of time. In turn, there would be less self-regulation involved in the later stages of change. Scholars generally agree that self-control constitutes a major source of self-regulation (Baumeister et al.,
1994; Tangney et al.,
2004). Consequently, self-control may determine the long-term formation of behavior, rather than short-term variations (de Ridder et al.,
2012). Hence, self-control would be an important factor in the formation of automatization/habit (de Ridder et al.,
2012), which, in turn, would make a behavior less prone to depletion of self-control resources (Hagger et al.,
2016). This is in line with the above-mentioned study by Sonnentag and Jelden (
2009) who assessed routines for off-job activities as a measure of automatization/habit. The authors showed that routines for off-job activities were positively related to leisure time sports activities. However, routines for off-job activities did not moderate the relationship between daily levels of stress at work and subsequent physical activity after work (Sonnentag & Jelden,
2009).
In summary, with the assumed effects of different levels of habituality of physical activity, the current findings are more consistent with previous research, which mainly focused on inactive individuals. Choi et al. (
2010), for example, found effects of work stress on physical activity after work in a sample of 2019 workers (age range 32–69 years) where merely 15% of the participants were moderately to vigorously active. In the present sample, the percentage of participants who did not perform MVPA after work was only 5.2%. Of those who were moderately to vigorously active, 80.4% performed at least 30 min of MVPA per day. These activity levels include a certain possibility of habituality, which, as described above, may be less affected by daily stressful experiences. Our dataset does not allow interpretations of this mechanism due to the fact that levels of habituality of physical activity were not assessed. Nevertheless, in an occupation as policing, for many employees, physical activity and resulting fitness are necessary components to execute services safely (for the officers themselves and for coworkers). Therefore, exercise training is part of professional education, fitness tests are common practice, and sport facilities are easily accessible, which reflects a certain cultural integration of physical activity behavior (Waters & Ussery,
2007; Westmarland,
2017). While stress has been shown to influence a multitude of health behaviors (Park & Iacocca,
2014), dispositional self-control has been shown to be more important to some behaviors than others (de Ridder et al.,
2012). Due to these circumstances and the additional relevance of shift work, other health behaviors (such as eating behavior) may be more prone to varying levels of psychosocial stress in police officers (Can & Hendy,
2014; Westmarland,
2017).
In this respect, we want to highlight the positive correlation between dispositional self-control and psychosocial stress in the present data. This result is in line with previous research on the direct association between dispositional self-control and psychosocial stress (Galla & Wood,
2015; Nielsen, Bauer, & Hofmann,
2020). The evidence base, however, is small and mainly relies on student samples; hence, the present study is one of the first investigations providing evidence in an occupational setting. Galla and Wood (
2015) explained the effect of self-control on stress experiences with the dual-process model (Strack & Deutsch,
2004), in which automatic processes stand opposite costlier reflective processes. These automatic processes are thought to be efficient responses with little to no conscious awareness or intention involved. Reflective processes, on the other hand, are costlier higher-order processes that take more time to process and involve intention. Therefore, intention-oriented behavior is generally rooted in reflective processes and eventually becomes habitual over time. Following Galla and Wood (
2015), self-control has to be exerted when reflective and automatic processes are in conflict. With lower resources available, for example, if psychosocial stress is high, automatic processes are more likely to determine thoughts, emotions, and behavior. In these situations, individuals with higher levels of dispositional self-control are more able to exert reflective processes and follow their long-term goals. The capacity to shift towards reflective processes has been termed thought control ability and was shown to be a strong predictor of psychological health and well-being (Luciano, Algarabel, Tomás, & Martínez,
2005). Taken together, while coping mechanisms may influence health behavior, self-control may alter stress appraisals in the first place. Hence, dispositional self-control may buffer the effects of psychosocial stress on health behaviors, by changing the stress experience/exposure (Nielsen et al.,
2020). This, however, would cover the measurable effects of psychosocial stress experiences on health behaviors. This proposed mechanism is speculative at this point. Based on the data presented here, we can merely state that self-control seemed to alter stress experiences in police officers.
The strength of our study was that we examined our research question in a naturalistic setting with psychometric data being assessed in almost real-time. This novelty is an advantage over previous work because of its high external validity and a lowered recall bias. Furthermore, we controlled for fitness levels, which is an important factor in the relationship between affect and intensity of physical activity (Lutz et al.,
2010). Despite these advantages, the findings of the present study have to be interpreted with caution due to several limitations. These limitations include the use of a convenience sampling method, a relatively high level of physical activity in the sample, as well as an uneven gender distribution, which may be representative of a general police force, but not a general population. Based on the increased standard error related to the interaction term in statistical analyses, the present sample size may have been a limiting factor in detecting significant main and interaction effects. Furthermore, while the applied methodology offers realistic insight in the acute stress perception of police officers, the assessment did not take place in a controlled setting. Therefore, it could be argued that the stress experiences at work may not have been sufficient to show effects on health behavior. However, theory as well as empirical evidence unanimously support the assumption that police officers encounter a multitude of occupational stressors and that resulting perceived stress is accordingly high (Arial, Gonik, Wild, & Danuser,
2010; Gerber, Hartmann, Brand, Holsboer-Trachsler, & Pühse,
2010; Simons & Barone,
1994; Violanti et al.,
2017). In order to approach this issue in future research, assessment over longer periods of time could be considered in order to increase the chances of variability in stress experiences. The assessment of daily stress over several weeks would lower participant’s ability to anticipate stress levels. This approach would further reveal whether physical activity levels differ on days with low, moderate or high stress levels and further facilitate within-person analysis.