Psychophysiological relationships between a multi-component self-report measure of mood, stress and behavioural signs and symptoms, and physiological stress responses during a simulated firefighting deployment
Introduction
Wildland firefighters face extended periods of physical work and restricted sleep in the line of duty (Aisbett et al., 2012, Cater et al., 2007, Phillips et al., 2015). For personnel deployed to fight campaign fires, demands involve high-intensity, intermittent physical tasks (Aisbett et al., 2007), performed across consecutive long shifts (i.e., 12 to 15-h) separated by restricted sleep opportunities (i.e., 3 to 6 h; Cater et al., 2007, Vincent et al., 2015a, Vincent et al., 2015b). When exposed to stressors such as physical work and sleep restriction, psychological and physiological stress responses are activated to maintain homeostasis over immune, hypothalamic-pituitary-adrenal (HPA)-axis and psychological functions (Dhabhar and McEwen, 2006, Maier and Watkins, 1998). However, severe occupational stressors can result in maladaptive physiological and psychological changes, including a deterioration in mood (Lieberman et al., 2005), dysregulated release of cortisol from the HPA-axis (Smith et al., 2005, Wolkow et al., 2015) and cytokines from the immune system (Huang and Acevedo, 2011). Prolonged changes have been implicated in the pathophysiology of cardiovascular disease (CVD), insulin resistance and depression (McEwen and Seeman, 1999, Pradhan et al., 2001, Ridker et al., 2000, Zunszain et al., 2011).
Stress-induced changes in psychological responses (e.g., mood) are closely related to, and possibly influence physiological processes (e.g., cytokines and cortisol; Kemeny, 2007, Marsland et al., 2007, Wright et al., 2005) via a bi-directional communication network between the brain, HPA-axis and immune system (Maier, 2003, Maier and Watkins, 1998). In addition, research shows how inflammatory and hormonal responses may signal the brain and have an effect over changes in mood, behaviour and cognition (Maier, 2003, Maier and Watkins, 1998, Slavich and Irwin, 2014). However, the potential utility of self-report measures to reflect and monitor firefighters' immune and hormonal responses on the fire-ground presents as a novel application of the subjective load monitoring approach adopted in sport settings (Saw et al., 2015, Saw et al., 2016). Compared to collecting and analysing biomarkers, monitoring these responses with self-report measures of mood, stress and behavioural signs and symptoms represents a less invasive and more practical option for fire agencies.
In physically demanding sport, the use of subjective measures of recovery-stress state and training load by Brink et al. (2010) and Anderson et al. (2003) respectively, have been related to incidents of injury and illness among soccer (Odds ratio 1.01 to 2.59) and basketball players (r = 0.675). Growing support for use of self-report measures as low cost monitoring tools to gauge athletes' physiological responses and mitigate injury and illness have resulted in their widespread application to diverse sporting contexts (Saw et al., 2016, Taylor et al., 2012). Among the tools, self-report measures employing a multi-component (e.g., mood, stress, behavioural signs and symptoms) approach are predictive, user friendly and more informative than those capturing single psychological constructs (Kellmann, 2010, Main and Grove, 2009, Saw et al., 2015). Accordingly, multi-component scales are frequently utilised in sport contexts and their relationship with physiological responses examined. For example, Main et al. (2010) investigated the relationship between inflammatory cytokine levels and self-report measures of overload in rowers completing an 8-week training course using the multi-component training distress scale (MTDS). Multiple relationships were identified between factors on the MTDS and cytokines (Main et al., 2010) that previous studies have had to use different, single construct tools to detect (Robson-Ansley et al., 2009, Wolkow et al., 2016), highlighting the convenience and breadth of the MTDS which includes the factors; depressed mood, vigour, physical signs and symptoms, sleep disturbance, perceived stress and general fatigue.
Despite success using a psychophysiological approach in athlete load monitoring contexts, limited research has investigated the ability of subjective measures to reflect stress-related physiological changes in occupational settings, such as firefighting. In our recent work (Wolkow et al., 2016), an increase in subjective fatigue was positively related to increased IL-6, TNF-α, IL-10 and cortisol among sleep restricted firefighters performing multiple days of physical work. Using a separate mood questionnaire (Mood Scale II; Thorne et al., 1985), we also found an increase in mood dimensions related to negative affect (e.g., fear) among sleep restricted firefighters were associated with a rise in TNF-α (Wolkow et al., 2016). Subjective pain ratings during 12 nights of sleep restricted to 4-h were also strongly associated with elevated IL-6 in a study by Haack et al. (2007). However, previous findings are inconsistent, with other studies reporting no association between negative mood and cortisol during physical work (Filaire et al., 2004) or sleep loss (Bouhuys et al., 1990). Although insights are gained from examining physical work or sleep loss in isolation, fighting wildfires exposes personnel to a combination of these stressors (Aisbett et al., 2012). Accordingly, determining the impact of sleep restriction while performing simulated physical firefighting work on psychophysiological responses is needed.
Physical work and sleep loss related stressors that elicit psychophysiological relationships in occupational settings highlight the potential usefulness of sport-based, multi-component questionnaires to monitor physiological changes among firefighters. Therefore, the aim of the current study was to investigate how possible changes in MTDS factors related to cytokine and cortisol levels among firefighters completing multiple days of simulated physical firefighting work, with and without restricted sleep. We hypothesised that when sleep restricted, firefighters performing physical work would display adverse subjective psychological responses across a range of measures (depressed mood, general fatigue, perceived stress, physical signs and symptoms, sleep disturbances, vigour) that related to elevations in cytokines and cortisol.
Section snippets
Participants
Wildland volunteer and career firefighters were recruited from state and territory-based fire agencies throughout Australia to maximise the generalisability of potential findings to rural firefighters nationally. For statistical purposes, participants were matched by sex, age and body mass index (BMI; p > 0.05; Table 1), and randomly allocated to either a control (CON) or sleep restriction (SR) condition. All participants completed a general health questionnaire to screen and subsequently exclude
MTDS and cytokines
The LMM with the lowest AIC for each of the cytokines was the full fixed effects Independence model, which after inspection of the AIC and ∆ AIC, was considered to have the best fit to model the relationship between MTDS factors and log IL-6, IL-8 IL-10, IL-4 and raw TNF-α. There were no significant interactions between any of the MTDS factors and IL-1β (p > 0.05).
Discussion
The current study investigated relationships between subjective responses on the MTDS and physiological changes during a 3-day simulated firefighting deployment, with and without restricted sleep. Consistent with the psychophysiological literature, findings indicated several significant relationships between the MTDS factors and cytokine and cortisol responses among firefighters. In support of our hypothesis, firefighters who received a 4-h sleep demonstrated increases in the MTDS factors
Conclusion
The current study provides a further step in our understanding of acute relationships between psychological, cytokine and cortisol responses in an occupational setting. Moreover, the findings extend the psychophysiological literature to multi-component self-report measures and highlight their suitability for use in firefighting populations to detect and monitor acute psychological changes that reflect physiological responses. Future research that establishes thresholds for subjective factors
Acknowledgements
This work was supported by the Bushfire Cooperative Research Centre.
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Present affiliation: Monash University, Faculty of Medicine, Nursing and Health Sciences, Melbourne 3004, Australia.