Chronic work stress and decreased vagal tone impairs decision making and reaction time in jockeys
Introduction
Professional athletes operate in competitive, highly stressful, and often dangerous environments, where decision making and reaction time can not only mean the difference between winning and losing, but can also have implications for their personal safety. Unsurprisingly, by the nature of their occupations, elite athletes are at increased risk of injury and death at work (Bureau of Labor Statistics, 2006). Therefore, understanding the factors that precipitate and contribute to this increased risk is vitally important. One factor that may contribute to these adverse outcomes is stress. Several lines of evidence have demonstrated an inverse relationship between acute stress and decision-making (Starcke and Brand, 2012), and chronic psychosocial stress is known to be an antecedent to athletic injury (Ivarsson et al., 2014, Williams and Andersen, 1998). Unlike any previous study, we will examine this problem through the use of a validated occupational stress model, considerations of stress physiology and experimental models of decision making.
The effort-reward imbalance (ERI; Siegrist, 1996) model of occupational stress is based on the philosophy of social reciprocity, with stress theorised to manifest when effort is not matched by reward. Adverse stress outcomes are likely when ERI ratio scores are >1 (Siegrist, 2010). Additionally, the ERI model has an intrinsic component, overcommitment (OC), which reflects the disposition/cognitive style of the individual, and reflects poor coping and an inability to ‘turn off’ from work. The ERI model proposes that efforts, rewards, and OC will be associated with ill-health indices, and that the interaction of efforts and rewards (e.g., ERI ratio) will explain more than these constructs in isolation. Large prospective studies of the ERI model have shown associations with a number of disease states, maladaptive behaviours, and poor health perceptions (Eddy et al., 2016, Siegrist and Li, 2016), and in recent times this has extended to include a growing number of studies with physiological measures as outcomes (Bellingrath and Kudielka, 2016). There is support for generalising the ERI model to professional athletes, with an imbalance between the perceived costs and rewards of professional Swedish athletes related to burnout (Gustafsson et al., 2008), but to the author’s knowledge, the ERI model has not been used with athletes. Similarly, little work has assessed the association of ERI with short term outcomes such as cognition, and especially reduced speed and accuracy of decision-making, which is very likely related to increased workplace injury.
The relationship between acute stress and decision-making (broadly defined here as the speed and accuracy of choices), has included several acute stress and decision-making paradigms, although the findings have been inconsistent (see Starcke and Brand, 2012 for a review). Only a handful of studies however, have assessed the association between chronic stress and decision-making. For example, higher chronic stress as measured by critical life events has been associated with more errors in decision-making and faulty information processing strategies (temporal narrowing, pre-mature selection, and non-systematic scanning of potential answers to a series of multiple choice questions), but only in individuals who were more sensitive to inner sensations (Baradell and Klein, 1993). In a study of university students, those reporting higher chronic stress performed more poorly on a monetary decision-making task, with the researchers suggesting a bias towards short-term thinking in those that reported being stressed, and thus making poorer overall choices (Gray, 1999). Similarly, a study of females experiencing chronic burnout, had decreased accuracy and reaction time on a visual and auditory continuous performance test when compared with a healthy age-matched sample (Sandström et al., 2005) To our knowledge, only one study has assessed the chronic effects of stress on decision-making using physiological indices of stress. The investigators reported that lower basal levels of cortisol were related to dysfunctional decisions in a gambling task (van Honk et al., 2003). The understanding of the relationships between stress and the speed and accuracy of decision-making is compromised however, due to the heterogeneity of individual physiological reactions (Sapolsky, 2015) and issues such as self-report bias (Macleod et al., 2002), and the possible time-lag surrounding the self-report of stress (Hausser et al., 2011). These limitations can be overcome by utilizing within group designs and physiological measures of stress in combination with the ERI model.
Physiological measures of stress are important as recent experimental evidence reveals that people may exhibit physiological signs of stress well before they are subjectively aware of being stressed (Hausser et al., 2011, O’Donnell et al., 2015). Alongside the decrements reported in decision-making due to chronic stress (Starcke and Brand, 2012), cognitive impairment (e.g., reduced episodic memory, reduced perceptual learning) has also been associated with increased glucocorticoid secretion (Wolf, 2009), with suggestions that dysregulated chronic stress physiology may contribute to the relationship between perceived stress and impaired psychological functioning (Dinse et al., 2017). Another index of the chronic stress response is heart rate variability (HRV). The low frequency to high frequency ratio (LF/HF) index of HRV provides information on the interplay between the sympathetic and parasympathetic nervous system response, with a higher LF/HF ratio indicative of increased sympathetic to parasympathetic dominance, chronic stress, and future morbidity (Thayer et al., 2010, Tsuji et al., 1994).
Due to the nature of horse racing which involves managing heavy animals at high speed in close proximity to other horses, fast and accurate decision-making is required and decrements in this area can lead to poor decisions with dire outcomes. Jockeys are at high risk of injury (Cowley et al., 2007, Hitchens et al., 2009), and this may be compounded by chronic stressors that include managing their diet and weight, and working long hours, while rewards are received sporadically (Dabscheck, 2015). We will also assess decision-making either side of an acute stressor, to determine if increased physiological arousal buffers jockeys from the decrements in decision-making and reaction time anticipated for those reporting more chronic stress.
We will assess if ERI is associated with dysregulated (acute and chronic) stress physiology and impaired decision-making and reaction time in both high and low stress periods. We also expect naturally occurring high and low stress periods to correspond with perceptions of stress and health and with objective measure of decision-making and stress physiology. Consistent with Siegrist’s assertion (2010), we anticipate that ERI ratio scores >1 will be associated with signs of dysregulated physiology and decreased decision-making. And finally, we will assess if indicators of dysregulated stress physiology moderate the association between ERI and decision-making.
Section snippets
Participants
Full-time professional Australian apprentice jockeys provided data at two time-points (September N = 42, November N = 32) and were aged between 16 and 24. Males (n = 14, M age = 18.1 SD = 1.5) and females (n = 18, M age = 19.9 SD = 2.3) participated, representing 64% of all apprentice jockeys in the region. Participants self-excluded themselves from the study if they were taking any medication (other than the contraceptive pill), were presently ill, or had a chronic health, thyroidal, heart, or psychiatric
Comparisons across time points
The ERI was positively related with an increased CAR in the low stress period, and negatively related in the high stress period (Table 1), possibly suggesting a blunted CAR (see Table 2) in the high stress period. Higher ERI scores were related with decrements in all decision-making tasks in the high, but not low, stress period (Table 1). The rewards component appeared most responsible for the association (ERI with decision-making), with rewards related with all decision-making tasks in both
Discussion
The comparison of jockeys above and below the ERI ratio cut-off in the high stress period suggests substantially impaired decision-making and choice reaction-time for the high stress group. Although the acute stressor (MAST) successfully induced a physiological stress response, none of the decision-making measures differed pre or post MAST in the high or low stress periods. Higher ERI correlated with a more elevated CAR in the low stress period, and with a smaller CAR in the high stress period.
Conclusions
Jockeys are said to have the most dangerous job on land, with a higher risk of fatality than other occupations traditionally considered ‘dangerous’ such as pilots and flight engineers (Bureau of Labor Statistics, 2006). Understanding the factors that may contribute to injuries and deaths is of considerable importance. Our findings highlight that in particular, decreased perceptions of reward (status, esteem, money) were most related with decrements in decision-making in both high and low stress
Conflict of interest
This research was not funded by an external body and the authors have nothing to disclose.
Acknowledgements
KL was supported by an Australian Government Research Training Program Scholarship. This research was supported from funding from the Sport, Exercise and Rehabilitation Research Focus Area, La Trobe University. We thank Paul Xanthos for assistance with heart rate variability analyses.
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