This study assessed the impact of a 2-week high-fidelity pre-hospital emergency medicine training course on psychobiological responding. Specifically, days of the training course, characterised by different learning, cognitive, and physical workloads, were compared in relation to markers of psychological and biological functioning. Analyses revealed significant differences in all variables across days, and consistent patterns with regards to the impact of different days upon psychobiological responding. The most consistent observation was a difference between training and non-training (weekend) days, where for all variables, reported levels at the weekend were statistically distinguishable from all training days. Specifically, the lowest levels of state, somatic, and cognitive anxiety, stress, and worry were reported at weekends. In contrast, compared to training days, the highest levels of self-confidence, perceived coping, and control, were reported at the weekend. Similar patterns were observed for biological measures where weekend days were among the lowest for heart rate and for levels of cortisol at Wake and during the CAR period.

While the identification of weekend, non-training days, does not speak directly to the aim of assessing the impact of high-fidelity training on psychobiological functioning, the consistent pattern of lower distress and biological responding, and higher perceived resources on non-training days, demonstrates the intended differences in load between days with training and no training. Furthermore, reduced responding at the weekend clearly demonstrates the capacity for recovery and provides further evidence of the adaptive nature of stress responding. That is, in preparation for, and during demanding, threatening, or stressful events, energy resources are mobilised via activation of the SAM and HPA axis. In contrast, in situations where perceived demand, threat, and stress are lower, the same level of resources are not required and responding can therefore be reduced. This pattern is evident during this course where the training days elicit higher levels of stress and demand and are accompanied by concomitant levels of biological responding compared with the weekend.

Although training days could be clearly differentiated from weekend days for every variable, there was less distinction across each of the training days which were characterised by similar patterns of distress and demand, and perceived coping and control. There were also similar patterns across training days for heart rate and HRV-derived stress, although there was a tendency towards greater levels of heart rate and HRV-derived stress in the second week of training. That is, for heart rate and HRV-derived stress, 4 of the top 6 highest values were recorded on days in the second week of training. The main exception was for Day 5 (Swift Water Rescue). This pattern of responding corresponds with the proposed cognitive and physical loads, where Day 5, and each day of the second training week, are categorised as medium to high load. The second week of the course involves the application of the skills developed in week 1 in complex scenarios. One day specifically however, emerged as distinct from all other training days. Day 10 (Road Traffic Collision: Day-Night) was characterised by the highest levels of state, somatic, and cognitive anxiety, stress, and worry, the lowest levels of self-confidence, coping, and control, and the highest levels of heart rate, HRV-derived stress, and cortisol levels at waking and before sleep. This day is split into two clinical scenarios which are designed to expose candidates to the demands of major incidents and mimic situations where demands exceed perceived resources. The day begins at midday rather than 9am to mimic a change in shift pattern and to facilitate a scenario that runs from dusk through to darkness. Both scenarios comprise several road traffic collisions alongside other ensuing emergencies, and involve complex decision making, multiple patients, and cross-working with additional emergency services. By this stage of the course candidates are expected to be fully immersed in the experience and care is taken to ensure that these scenarios feel as real as possible. Specific factors facilitating this realism include the use of actors, other emergency services, lighting, and simulated blood. Having a break between the two scenarios represents a gap between callouts such as would be experienced in real emergency care, and starting the second of the two scenarios at dusk adds an extra layer of realism and cognitive load. As such, this day is truly high-fidelity and is characterised by the highest learning, cognitive, and physical loads across the entire course. It is perhaps, therefore, not surprising that this day also elicits the greatest levels of psychobiological responding and the lowest levels of perceived coping and control.

The up- and down-regulation of biological responding to match perceived demand is adaptive [16], and demonstrates that the proposed learning, cognitive, and physical loads of each of the training days function as intended. These findings can be seen within the framework of the Job Demands-Resource theory [29] where increased stress arises from an imbalance between perceived work demands and job-related resources. This imbalance has been observed across a range of occupations where physical, social, or organisational aspects of a role require sustained physical and / or mental effort, and these requirements are not met with appropriate levels of resource that could buffer these demands. This is common of the lived experience of those that provide critical emergency care, where crisis situations are characterised by high levels of physical and cognitive demand, with low levels of control and perceived ability to cope [15]. The provision of emergency care is stressful, and this demonstrates the importance of high-fidelity training to also comprise the emotional elements associated with real emergency situations [18].

In line with the study aim, we have demonstrated that training days with different learning, cognitive and physical loads, are characterised by differences in psychobiological responding. Specifically, those days with the highest proposed workloads are met with the highest level of psychobiological responding. However, to what extent do these findings represent experiences in real life emergency care? High fidelity training typically comprises environments that are realistic in terms of their physical (look, feel, sight and sound) and conceptual (level of realism) attributes, while less attention is paid to emotional attributes [30]. Indeed, emotional engagement is typically greater in simulations with higher levels of realism [31]. This study demonstrates the association between emotional responses, as evidenced by stress and worry, commensurate with workloads based on high-fidelity activities, but moreover, demonstrates the subsequent impact on biological responding as evidenced by measures of heart rate, HRV-derived stress, and cortisol indices. This course comprises the key ingredients for high fidelity simulation and the psychobiological responding is therefore analogous to that which would be experienced in real emergency care. Given the high-fidelity nature of the activities and timing, Day 10 represents a typical, albeit exceptionally challenging, day that is in line with the daily requirements of front-line emergency medicine. That this day is characterised by the highest levels of psychobiological responding, whilst adaptive in the short term, may be cause for concern in the longer-term, and emphasises the importance of the opportunity for recovery to avoid the negative consequences of repeated and sustained physiological activation on health and wellbeing through the manifestation of burnout. Burnout has a significant deleterious effect on health and wellbeing through sustained activation of the nervous and endocrine systems. This activation leads to increased allostatic load and widespread dysregulation of immune, digestive, reproductive, metabolic and cardiovascular systems, alongside changes in brain structure and function [32]. Burnout most often results from a prolonged, ongoing imbalance between work demands and job-related resources, whereby work demands significantly exceed job-related resources and this is a significant problem within medical professions [33]. This is evidenced in the sector where recent reports demonstrate that over 50% of those that provide emergency medical care are experiencing moderate to high levels of burnout [34].

This study should be evaluated in light of some limitations. Although we present evidence for the high-fidelity of the training course, the overall structure, with two blocks of five training days separated by a weekend, may be less representative of the on-the-job experiences of those that deliver emergency care. For these individuals, long hours, shift work including nightshifts, and atypical working weeks are commonplace [35], and the frequency and sustained physiological activation within these work patterns will increase vulnerability to negative consequences for health and wellbeing. Within the context of this training course, the lower levels of responding observed at the weekend represent adaptive responding and demonstrate that these participants, when afforded the opportunity, experience a lowering of biological responding that matches a reduction in their perceived distress and demand. Given the significant levels of burnout in this sector, this seems less representative of their lived experience, however, the extent to which there are opportunities for adequate recovery warrants further investigation.

In support of the notion that greater CARs are associated with increased demand [13], it would be reasonable to expect the greatest CAR on Day 10. Indeed, all other markers indicate this to be the most demanding day with the highest levels of anticipated and experienced demands, and concomitantly higher levels of HR and HRV-derived stress, and cortisol before sleep. However, the CAR was not of greater magnitude on this day. Later waking is associated with smaller CARs irrespective of demands [6], and this is likely reflected in this study where on Day 10 there was a planned later start which led to later waking (over 2 h later on Day 10 than any other training day). It is therefore likely that waking time has prevented full exploration of the greatest levels of anticipated demand being associated with the greatest CAR in this study. The greatest CAR magnitude was, however, observed on Day 8. This day was characterised by similar levels of anxiety, stress, worry, control and coping to other training days; however, Day 8 is the first day of the second week of training which participants anticipate being increasingly challenging. This anticipation of forthcoming demand may drive this increased CAR in line with the view that increased CARs provide a preparatory boost at times of anticipated demand [6]. The measurement of cortisol, particularly measurements of diurnal cortisol and the CAR can be complex, and a range of factors must be considered in its collection, analyses and interpretation. It is therefore worth noting that expert guidelines [26] were followed in this study to maximise the integrity of sampling and to guide subsequent interpretations.

Heart rate and HRV-derived stress were obtained from commercially available smartwatches. There is an increasing interest in ambulatory monitoring and therefore an increased demand for non-invasive and efficient devices for the measurement of physiological variables [36]. Smartwatches may not afford the same level of accuracy as laboratory devices for some indices; however, a recent study has demonstrated that HRV derived from Garmin smartwatches provides excellent accuracy compared with gold-standard ECG-based HRV monitors [37]. Wearable devices are the most viable option for ambulatory studies and smartwatches are particularly acceptable to users. Indeed, our use of smartwatches is a novel aspect of this study design, and the same level of data collection would not have been possible without them. Another advantage afforded by the use of smartwatches is the volume of collected data. In the current study, smartwatches were worn continuously for the assessment period and these continuous data would allow for a more fine-tuned analysis of within day variations in heart rate and HRV-derived stress, including periods before, during and after the experience of stress. These analyses would be informative; however, they are beyond the scope of this paper, the main aim of which was to characterise training days by differences in psychobiological responding. As such, aggregated data were used to allow for consistent comparison. Future work could therefore consider a more detailed assessment of real-time changes in relevant indices. Future work could also consider the identification of factors that may predispose individuals to display particular patterns of psychobiological responding that may lead to negative consequences for health and wellbeing. Again, this is beyond the scope of the current study, where the sample size, which was prohibited by the capacity of the training course and the study duration, is not sufficiently powered to address questions related to individual differences.

Few studies have simultaneously assessed markers of the autonomic nervous and endocrine systems to stress in clinical or high-fidelity scenarios. Although some studies have incorporated indices of these systems [20], the focus has been on assessment surrounding a specific event rather than longer-term assessment. This study represents the longest continuous assessment of the impact of high-fidelity training scenarios in emergency care. Moreover, with the inclusion of a range of measures, this study is the most comprehensive assessment of psychobiological functioning in emergency medicine to date. It is suggested that, in addition to the simulation of environment and equipment to simulate real world scenarios, high-fidelity simulations should create realistic environments to the extent that they also elicit the emotional responses that would typically be experienced in real emergency situations [18]. This study clearly demonstrates these emotional responses, and additionally, the corresponding biological responding which would be typical in the delivery of emergency medical care.