The Use of Fitness Testing to Predict Occupational Performance in Tactical Personnel: A Critical Review

Tactical personnel work in an occupation that involves tasks requiring a high level of cardiovascular fitness as well as muscular strength and endurance. The aim of this literature review was to identify and critique studies investigating the relationship between physical fitness, quantified by fitness assessment measures, and occupational task performance. Databases were searched for relevant articles which assessed a fitness measure and a measure of occupational performance. A total of 15 articles were included and were deemed to be of acceptable methodological quality (8.4/12 on the Critical Appraisal Skills Programme checklist). Included articles assessed a variety of fitness attributes and occupational tasks. Across tactical groups, there appear to be no standardized fitness tests that can determine occupational performance, with aerobic fitness, anaerobic fitness, strength, endurance, power, and agility all being associated with occupational task performance. A wide range of fitness assessments appears to be required to predict occupational performance within tactical personnel. Efforts should be made to base fitness assessments on occupational demands unique to both the environment and requirements of each individual tactical unit.


Introduction
Tactical personnel, including military personnel, law enforcement officers, and firefighters, are required to undergo various physical tasks, all of which involve carrying external loads [1,2]. In military personnel, occupational tasks may include heavy load carriage and mobilizing through difficult terrain while enduring harsh environmental conditions [3,4]. The physical demands of law enforcement duties may include running, restraining perpetrators, self-defense, and manual handling tasks [5,6]. Likewise, firefighters are required to respond to emergency situations requiring search and rescue and protecting community property [7,8]. Firefighters also carry heavy equipment in addition to wearing their own protective gear, while working under severe heat stress at near maximal heart rates for prolonged periods of time [7].
These physically demanding occupational tasks conducted by tactical personnel require a high level of cardiovascular fitness as well as muscular strength and endurance [9,10]. Poor performance in these areas increases injury risk and may lead to mission failure, loss of life, or a perpetrator evading capture [11,12]. For example, Pope et al. [13] and Jones et al. [14] have found that military recruits who had a lower level of cardiovascular fitness, were at increased risk of injury in comparison to the fitter members of their group. Similar results have been found in other fitness measures including power [15], strength [16], and muscle endurance [17]. The relationship between fitness and occupational task performance is highlighted by Robinson and colleagues [18] who found that increased aerobic fitness and strength were associated with better load carriage performance in specialist police. Similarly, the findings from Hendrickson et al. [19] revealed that an 8-week aerobic endurance and strength training led to significant improvements in common tactical occupational tasks including load carriage and repetitive lift and carry tasks.
Due to the importance of fitness on injury risk and occupational task performance, initial trainees seeking employment in tactical populations are required to undergo a series of physical tests. These tests are aimed at assessing future performance [20] and identifying those most at risk of injury [21,22]. Despite the benefit of using many of these assessments, the use of both pushups and situps to determine occupational fitness has attracted wide criticism in the literature [23]. Carstairs et al. [24] found that both pushups and pullups only correlated to one out of four army task simulations. One of the problems identified in these assessments by Blacker et al. [25] was that they are typically performed without any of the additional equipment that tactical personnel are required to carry as part of their occupational requirements.
Although there appears to be a link between different fitness variables and performance in tactical personnel, debate still exists around the assessments used to measure these attributes, and whether a link between these measures of fitness is, in any way, associated with occupationally specific performance tasks. Therefore, the aim of this literature review was to identify and critique studies that investigated the relationships between physical fitness, quantified by fitness assessment measures, and occupational task performance.

Search Strategy
Search terms were developed based on a brief initial review of the literature and in consultation with subject matter experts. Initial terms were adjusted and refined based on the relevance of the re-occurring articles and eventually agreed upon through consensus from all authors. Databases searched included PubMed (https://pubmed.ncbi. nlm.nih.gov/?otool=iaubondlib: accessed on 1 November 2019) EMBASE (https://wwwembase-com.ezproxy.bond.edu.au/#/login: accessed on 1 November 2019), and Ebscohost (CINAHL and SportDiscus) (http://web.a.ebscohost.com.ezproxy.bond.edu.au/ehost/ search/selectdb?vid=0&sid=d8069b8b-e82d-45c6-96d2-9c8cba027660%40sessionmgr4007: accessed on 1 November 2019). These databases were chosen based on a large number of high-quality peer-reviewed articles present and the representation of journals relevant to the review topic. The finalized search terms and applied filters (where available) for the databases searched are summarised in Table 1.
After search terms were established and prior to the screening of the studies, inclusion and exclusion criteria ( Table 2) were developed. In order to evaluate the most current evidence, studies older than 15 years were excluded during the screening process. Duplicates were removed after the collection of all studies, with the remaining studies screened based on title and abstract for relevance. In order to minimize both search and selection bias, three reviewers were responsible for screening and the selection of relevant studies independently. A search was performed following the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines. The PRISMA flow diagram [26] ( Figure 1) summarizes the entire search process. (("Exercise Test") OR "Physical Fitness") OR "Assessment Screen Testing") AND (("Police") OR ("Firefighters") OR ("Military Personnel") OR ("Military Recruits") OR "Sheriff" OR "Incumbent officer" OR "Patrol Officer" OR "law enforcement") AND ("work * ADJ performance" OR ("Physical Fitness") OR "occupational ADJ skills" OR ("Task Performance and Analysis")) Search modes Boolean/Phrase 1136 * Denotes truncation of a word for database searches.

Critical Appraisal
All studies which met the criteria were critically appraised using the Critical Appraisal Skills Programme (CASP) checklist for cohort studies [27]. The checklist consists of twelve questions that evaluate the methodological quality of a study. Each question can be answered "yes", "can't tell", or "no", where one point was given for answers with "yes" and zero-point was given for answers with "can't tell" or "no". Questions seven and eight have to be answered with a short response rather than "yes", "can't tell", or "no"; therefore, those two questions were left blank due to subjectivity. Question five and six consisted of two sub-questions "a" and "b" which form a total possible score of 12 out of 12 questions. Methodological quality was also assessed individually by three authors to avoid bias.

Critical Appraisal
All studies which met the criteria were critically appraised using the Critical Appraisal Skills Programme (CASP) checklist for cohort studies [27]. The checklist consists of twelve questions that evaluate the methodological quality of a study. Each question can be answered "yes", "can't tell", or "no", where one point was given for answers with "yes" and zero-point was given for answers with "can't tell" or "no". Questions seven and eight have to be answered with a short response rather than "yes", "can't tell", or "no"; therefore, those two questions were left blank due to subjectivity. Question five and six consisted of two sub-questions "a" and "b" which form a total possible score of 12 out of 12 questions. Methodological quality was also assessed individually by three authors to avoid bias.

Statistical Analysis
Once the critical appraisal score (CAS) for each study was finalized, a mean score for each study was calculated along with a mean and standard deviation of scores for all studies. Krippendorff's Alpha was used to determine the inter-rater reliability by a fourth author (RO) who was independent of the CASP scoring.

Statistical Analysis
Once the critical appraisal score (CAS) for each study was finalized, a mean score for each study was calculated along with a mean and standard deviation of scores for all studies. Krippendorff's Alpha was used to determine the inter-rater reliability by a fourth author (RO) who was independent of the CASP scoring.
The mean critical appraisal score (CAS) score for all studies was 8.4 ± 1.2, ranging from the lowest being 6.33 [35] to the highest of 10.0 [29]. The level of agreement between the three raters, as measured by Krippendorff's Alpha, was 0.80 which was considered to be substantial agreement [42].
Power was measured by vertical jump height in three studies [36,40,41], standing long jump in two studies [29,31], and both 2 kg medicine ball put and 9 kg overhead throw in one study [29]. One other article assessed power via a single-leg knee extension power test at 50, 60, and 70% of 1 RM [37].
Subjective rankings of occupational relevance were assessed in two studies. The evacuation victim drag was subjectively rated as relevant to a 'large extent' or 'very large extent' by 81% of its participants [28]. The Officer Physical Ability Test (OPAT) for US law enforcement officers was rated as having excellent relevance [39]. Key data pertaining to the fitness measure utilized and the occupational measures conducted are found in Table 3 below.

Discussion
The aim of this review was to identify and critique studies that investigated the relationships between physical fitness, as measured by fitness assessment measures, and occupational task performance. Overall, the methodological quality of studies in this area appears to be of acceptable quality. Across tactical groups, there appear to be no standardized fitness tests that can determine occupational performance. This finding agrees with previous investigations which have suggested that multi-faceted fitness assessments are important to assess the various essential fitness components of tactical personnel which are often unique to each environment [39].
Aerobic fitness was found to be correlated with OPAT completion time and components of the OPAT [39] and with PAT performance [40] in police officers. It was also related to Military Occupational Specialties test performance [29] and military simulation tests in combat soldiers [31], loaded marches of 3.2 km and 29 km in elite soldiers [33] and field tasks [34], job performance tests [36], PAT [37] and fire fighting simulation tests [38] in firefighters. These results are not surprising given that high levels of aerobic fitness are paramount in tactical professions with research supporting its importance to tasks involving load carriage [18,43]; a common but important requirement within tactical populations. Furthermore, those with lower levels of aerobic fitness must work at a higher level of their overall capacity for a given task, leading to an earlier onset of fatigue [44]. This fatigue may lead to alterations in movement mechanics which in turn leads to injuries. As such, aerobic fitness deficits have also been linked to injury risk in military populations [13,14], Federal agents [45], and firefighters [46]; again highlighting the importance of aerobic fitness for both injury and performance and injury mitigation amongst tactical populations.
In a similar manner to aerobic fitness, measures of strength have also been associated with task performance and injury risk. Load carriage performance and victim drag ability, for example, have both been found to be associated with strength (both relative and absolute) in tactical personnel [18,47]. The carrying of a pack, for example, becomes part of an individual's body mass, or relative load, hence the relationship with relative strength [48]. Conversely, the victim drag task requires moving of an external or absolute load, hence the relationship with absolute strength. Lower limb muscular strength, specifically, was found to predict dummy drag performance in Navy operators [28], was a predictive component of Military Occupational Specialities tests [29], and correlated to repetitive box lifting tasks in soldiers [32]. Likewise, upper limb strength was correlated with army task simulations [24], ability tests [35], and job performance tests [36] in firefighters. Specific grip strength was associated with improved scores in tactical situations and marksmanship in police officers [41] while finger strength was associated with physical ability tests scores in firefighters [37].
Muscular endurance is often a focus of tactical training programs [49] and bears occupational relevance with the prolonged carrying of stores and pack marching [50]. Upper limb endurance was related to the PAT [40] and components of the OPAT in police officers [39], Army task simulation performance [24] and military simulation tests in soldiers [31], ability tests [35], and job performance tests [36] in firefighters. Likewise, lower limb endurance was related to job performance tests in firefighters [36]. Abdominal endurance was correlated with PAT [40] and OPAT [39] performance while abdominal endurance and strength was found to be important for firefighters' ability test performance [35]. The use of measures of muscular endurance, such as push-ups or sit-ups, may be more indicative of a global measure of fitness and are, therefore, questioned as relevant in fitness testing [51]. However, this is not to suggest that these measures are not of value, as poor holistic fitness can have second-order impacts on occupational fitness (e.g., increased workplace absenteeism due to illness) [52].
Lower limb power is an occupationally relevant attribute for seeking cover, fire and movement drills, and short sprinting [53,54]. Lower limb power was found to be correlated with evacuation tests in Navy operators [28], PAT performance in police officers [40], and ability tests in firefighters [35]. The ability to generate power in a vertical jump while wearing external load was correlated with military simulation tests [31]. Previous research has identified that declines in power development, measured via vertical jump height, is linked to a significantly greater risk of both injury and the development of illness in police personnel [15] highlighting the benefit of lower limb power as a measure of task performance and injury risk in the tactical field.
Agility was correlated with overall OPAT time and components of the OPAT in police officers [39] while anaerobic power was found to be associated with physical ability test time in firefighters [37] and evacuation tests in Navy operators [28]. No relationship to task performance was found for measures of flexibility in this review, with the flexibility of the hamstrings, in particular, being challenged as a risk factor for injury in general [55], querying the effectiveness of this measure for either injury risk or task performance.
A limitation to this review was the inability to screen for non-English studies which reported on physical fitness and its relationship to task performance. This may have narrowed the body of literature from which conclusions could be drawn. Some further limitations arise from the articles that comprise this review being of only 'acceptable' quality. The wide range of fitness assessments studied could be viewed as a limitation. This is most likely due to the wide variety of occupational tasks which occur across the tactical professions, which, while indicative of tactical populations, does make fitness assessment protocol standardization challenging.

Conclusions
A wide range of fitness assessments appears to be required to predict occupational performance within tactical personnel. Despite aerobic fitness assessments being the most highly studied and closely related to occupational performance, other measures of great importance include muscular strength, endurance and power, agility, and anaerobic capacity. Efforts should be made to base fitness assessments on occupational demands unique to both the environment and requirements of each individual tactical unit.

Conflicts of Interest:
The authors declare no conflict of interest.