Exploring heart rate variability as a human performance optimisation metric for law enforcement

  • Colin Tomes

Student thesis: Doctoral Thesis


Tactical personnel, inclusive of police officers, face complex challenges over potentially decades-long careers. These cumulative exposures may manifest as allostatic load, impairing health, fitness, and performance. Allostatic load describes increased vulnerability to psychophysiological dysfunction resulting from prolonged overstress exposure. Monitoring for this risk is an important step towards its mitigation. Heart rate variability (HRV) analysis can noninvasively acquire psychophysiological overstress information in tactical environments. HRV theory and principles are well established, however, the integration of HRV in tactical workflows, especially for end-users, has received limited research attention. Therefore, the overarching aim of this programme of research was to determine the utility of HRV assessment in the support of specialist police and their organisations and to alert stakeholders to potential instances of psychophysiological overstress.

Chapter 1 introduces HRV concepts within tactical contexts. Components of tactical work that may be best appreciated with HRV analysis are highlighted. Principles in this introduction are further articulated in a systematic review (Chapter 2). Chapter 2 reports on the undertaken systematic review which summarised and critically appraised studies of HRV applications across tactical populations. Of 296 initially identified studies, twenty were included. The volume of evidence suggested that HRV effectively supports health and performance measures in tactical environments. However, literature gaps were identified; most notably, there was limited evidence available regarding HRV in specialist police professions, thus warranting this research. As professional requirements and potential allostatic load sources differ during specialist police selection and subsequent specialist police operational contexts, two research arms were devised to pragmatically address this critical gap. Chapter 3 illustrates the research structure in further detail and outlines which studies address specific literature gaps within specialist police and in which of the two developed research arms. Methodological approaches are also described.

Chapters 4, 5, 6, and 7 encompass HRV application in initial specialist police selection. Chapter 4 introduces the first field study, building on the findings from Chapter 2 (Studyiii1) that HRV assessment may be more valuable than traditional heart rate (HR)measurement for monitoring tactical training as HRV is capable of measuring stress holistically. The primary aim therefore was to investigate whether HRV was more sensitive than HR at monitoring workload during specialist police selection activities. As aerobic fitness is associated with workload during these tasks, a secondary aim was to investigate relationships between HRV, HR, and maximal aerobic fitness. As illustrated by a time-series plot, HR values were unremarkable while HRV values were potentially depressed, and tentatively indicative of overstress. Estimated maximal aerobic fitness (20-m shuttle run) was significantly positively correlated with HRV, but there was no relationship with HR. When a linear regression model was applied, neither HRV nor HR were predicted by 20-m shuttle run scores.

Chapter 5 aimed to determine the effectiveness of HRV in differentiating between candidates that failed to complete specialist selection from those who succeeded. HRV was defined as the percentage of R-R intervals that varied by at least 50ms (pRR50). Data were summarised in a heat map. A logistic regression model was generated that effectively predicted attrition but did not identify the most successful candidate. Therefore, the aim of Chapter 6 was to profile HRV characteristics of that successful candidate and consequently a detailed HRV time series plot was generated. Contextual analysis was applied, and the candidate demonstrated continued performance even under apparent duress, both physical and psychological in nature. The subsequent studies (7-9)then aimed to consider HRV monitoring at the operational level where such duress exposures occur frequently.

Noting that success in training is distinct from operational performance, Chapters 7, 8, 9,and 10 examined the use of HRV monitoring in operational contexts. The purpose of Chapter 7 was to identify if HRV analysis could classify candidate performance in specialist police selection during occupationally realistic tactical operations scenarios which required fluid psychomotor skills, teamwork, and leadership while under duress. Qualitative analysis of descriptive statistics indicated that the HRV data of one participant were substantially different from his peers. This candidate was also the highest performer, suggesting a relationship between HRV and occupational aptitude.

Given that specialist police often work rotating shift schedules which may lead to sleep deprivation, introducing another source of allostatic load, the aim of Chapter 8 was to determine the extent to which HRV may detect differences between specialist police that worked an overnight shift and those that were off duty overnight. HRV was analysed in11 male specialist police officers who were either off-duty or on overnight duty prior to engaging in specialist assessment activities. All officers experienced HRV perturbations from the assessment, but post-assessment HRV was greater amongst those who were coming on duty. HRV values continued to decline after assessment success amongst those that worked the night prior to training, potentially indicating greater stress loads in those that worked the overnight shift.

Chapter 9 further explored HRV changes observed in Chapter 8. The aim was to identify relationships between physical fitness as measured by completion time on a primarily anaerobic occupational obstacle course, and HRV response during firearms qualification and subsequent stress training. HRV was assessed as the within-operator change from pre- to post-qualification and post-training. HRV was reduced after training but not after qualification. A linear regression model indicated that obstacle course completion time predicted HRV changes from baseline to both post-qualification and post-training.

While stressful training and overnight shifts are regularly encountered in specialist police work, other tasks, such as serving in Directing Staff (DS) roles on selection courses for future candidates are also important duties and present as a nexus between operations and selection. Thus, Chapter 10 considered the critical operational role of DS cadre. The purpose of this study was to monitor and analyse the HRV of one DS member during their 24-hour shift on a candidate selection course. The findings of this case study suggested that DS may be subject to stress levels not unlike those of candidates. This is of note as selection courses are highly taxing and arduous, and officers may serve as DS on more than one course per year and still be required to perform their operational duties.DS requirements during selection courses should therefore be considered appropriately in the overall deployment and operational task scheduling paradigm.

Each previous chapter considered important elements of service in a specialist police organisation. The final chapter (Chapter 11) summated the findings from this programme of study, contextualised the works in terms of the bodies of literature with which they were most associated, and highlighted overall limitations as well as plausible future directions. A final supplementary chapter, aimed to provide an operational guide for utilising HRV data in tactical settings, contributed to further support translation of research to practice. In this supplementary chapter, shortcomings of using HRV were reviewed and solutions to avoid flawed analysis provided, as are the key lessons learned from this thesis. In essence, the presentation and visualisation of HRV data may be as critical to the application of HRV analysis as the measurements themselves in tactical settings.
Date of Award8 Feb 2024
Original languageEnglish
SupervisorRob Orr (Supervisor), Ben Schram (Supervisor) & Elisa Fontenelle Dumans Canetti (Supervisor)

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