Examining the Relationship between Firefighters' Performance on Physical Ability Test and Measures of Blood Pressure, Pulse Rate, and Aerobic Capacity

2.1. Study Design and Population

In the current study a secondary analysis of data collected by the City of Cape Town Fire and Rescue Service (CoCTFRS) was conducted. The data included the physical ability test (PAT) that was conducted by the Fire Services during their annual wellness and Fitness assessment. The data included demographic information, such as age, sex, height, and weight. In addition, data were collected on firefighters' resting heart rates and blood pressures, and post-PAT heart rates and blood pressures. In total, data were collected on 599 male and female full-time firefighters, with ages ranging between 20 and 65 years, as this is the typical retirement age for firefighters. Approval to analyze the secondary data was provided by the Chief Fire Officer and the head firefighter in charge of the wellness and physical fitness assessment. Additionally, all firefighters provided their consent for the data to be used for research purposes. Ethical clearance was granted by the University of the Western Cape (UWC) Biomedical Research Ethics Committee (BMREC) (ethical clearance number: BM21/10/9). Additionally, the Helsinki Declaration has been adhered to in this study. During data collection, all participating firefighters were informed that their written informed consent was obtained before proceeding. The period of data collection spanned from July to August 2022.

2.2. Sampling and Participant Recruitment

Data collection took place at a single fire station located in the South District in the Cape Town Metropolitan area. Furthermore, to ensure consistency in terrain, environmental conditions and testing surface, data was collected on dry days with cool temperatures. All physical measurements and PAT tasks were gathered and recorded by qualified firefighters and researchers who were familiar with all testing equipment and research protocols to ensure the consistency and reliability of the test results. All full-time firefighters, regardless of age, who had passed the initial health assessment were tested and included in the data set. Firefighters on sick leave, in administrative duty, with seasonal or part-time employment, or who did not participate in the PAT were excluded from the study. Firefighters who failed to pass the pre-PAT assessment, such as those with elevated blood pressures (systolic blood pressures above 180 mmHg and diastolic blood pressure above 105 mmHg), those with underlying cardiovascular disease (CVD), or those with signs and symptoms of CVD (angina, chest pressure, dyspnea, dizziness or fainting) were excluded from participation.

2.3. Physical Ability Test

The Fire and Rescue Service in the City of Cape Town utilized occupational-specific tasks to evaluate operational performance, following the testing protocol outlined in the wellness manual. The PAT is a standardized work ability assessment that all firefighters are required to pass when becoming firefighters. This is then used to test the firefighters’ occupational readiness annually. Collaborating with industry professionals, the CoCTFRS incorporated these tasks into their fitness and wellness program to mimic the challenges firefighters encounter. These tasks aimed to replicate the physical demands and strains faced by firefighters during their duties. Participants were required to complete a simulation protocol within 9 minutes (540 seconds), with 20 seconds allotted for recovery between tasks, while wearing full PPE and breathing apparatus. The simulation comprised six tasks designed to simulate various stressors encountered by firefighters: step-up (SU), charged hose drag and pull (CHDP), forcible entry (FE), equipment carry (EC), ladder raise and extension (LRE), and rescue drag (RD). Each task had specific completion time requirements, and failure to meet them resulted in a “not yet competent” grade on the Physical Ability Test (PAT). The SU task mandated 30 repetitions on a standardized 200 mm platform within 90 seconds. For the CHDP, firefighters had to drag a tire 27 meters and then pull it an additional 15 meters within 180 seconds. The FE task involved driving a 6-kg sledgehammer to move a tire 600 mm in under 60 seconds. In the EC task, firefighters had to remove two 25 kg foam drums from a 1.2-meter platform, carry them 25 meters, return 25 meters, and place the drums back within 90 seconds. For the LRE, firefighters had to position a ladder against a building, hoist a 35 kg drum using a hauling line, and lower it within 90 seconds before returning the ladder to its original position. Lastly, the RD required firefighters to drag an 80 kg tire 11 meters, execute a 180-degree turn, and continue for another 11 meters within 60 seconds. The protocol used was used previously in a study conducted by Ras et al. [17]

2.4. Height, Weight, Blood Pressure, Heart rate and Aerobic Capacity Measurements

Height was measured using a standardized portable stadiometer (Seca portable stadiometer), with firefighters standing barefoot and their heads positioned in the Frankfort plane [36]. The weight of the firefighters was measured with firefighters wearing minimum clothing (shorts for males and shorts and a t-shirt for females) using a calibrated precision weight scale [36]. Body mass index (BMI) was calculated using the formula: (kg)/(height (m))^2. Blood pressure was measured using a blood pressure cuff and a Sphygmomanometer, the standard auscultatory technique employed by trained paramedics. When taking blood pressure, firefighters were instructed to remain seated for five minutes prior to testing. Blood pressure was taken, in a seated position, twice and if blood pressure varied more than 2 mm Hg, blood pressure was taken for a third time. Heart rate was taken using a pulse oximeter (SantaMedical Finger Pulse Oximeter). Additionally, heart rate was measured for 60 seconds to ensure the accuracy of the readings. Aerobic capacity was estimated using the heart rate ratio formula: VO2 max = 15.3 x (HRmax ÷ HRrest) [37]. Heart rate max was estimated using Tanaka’s formula, i.e., HRmax = 208 − 0.7 × age [38]. Once the firefighters had completed the PAT, they performed the PAT, where they were asked to remove their breathing apparatus and jacket and then remain seated for five minutes before their blood pressure was taken. Blood pressure and heart rate differences were calculated by subtracting post-PAT measures from pre-PAT measures.

2.5. Statistical Analysis

The data were cleaned and coded using a Microsoft Excel spreadsheet. Thereafter, the data were imported into a statistical software package, namely SPSS® software, version 29 (Chicago, Illinois, USA), and analysed. Descriptive statistical analyses, such as the mean and standard deviation. Thereafter, group comparisons were performed using the independent samples t-test and the one-way analysis of variance (ANOVA). Univariable and multivariable linear regressions were conducted to determine the sociodemographic characteristics and cardiovascular health measures (blood pressure and heart rate) that were significantly associated with performance on the PAT. In addition, logistic regression was used to assess the association between demographic characteristics, blood pressure, heart rate, and overall pass rates for the PAT and pass rates for each PAT task, i.e., SU, CHDP, FE, EC, LRE, and RD. Three models were used to assess the effect of confounding factors on occupational performance. For the linear and logistic regression models, Model 2 was adjusted for age and sex and Model 3 was adjusted for age, sex and aerobic capacity. For all models, the PAT completion times, PAT pass rates, and pass rates for each PAT task were considered as the dependent variables. The independent variables included measures such as height, weight, BMI, SBP, DBP and pulse rate. To ensure that significant collinearity and multicollinearity were not present, which could impact the statistical outcomes, the variance inflation factor (VIF) and Durbin-Watson statistics were used. In addition, a test statistic of between 1.5 and 2.5 for the Durbin-Watson indicated the absence of autocorrelation, while a VIF <5 was used to demonstrate the absence of significant collinearity. For this dataset, the data was normalized using the fractional ranking and inverse DF, IDF.NORMAL transformation [39]. A p-value of <0.05 was used to indicate statistical significance.

3.1. Differences between Demographic Characteristics and PAT Performance

Table 1 presents the demographic characteristics of the participants, categorized by sex and age groups. The mean age of the firefighters was 39.4 ± 10.0 years, with a mean weight of 85.4 ± 16.9 kg, height of 1.7 ± 0.1 m, and BMI of 27.9 ± 6.7 kg•m-2. Males were significantly heavier (p = 0.009), taller (p <0.001), and had higher SBP compared to females (p <0.001). Male firefighters were found to complete the PAT significantly faster than female firefighters (p <0.001). In addition, the resting heart rate was higher in females than in males (p = 0.003). There was a significant difference in BMI according to sex and age groups (p <0.001). Based on age groups, the oldest age group of firefighters (50 and older) had the highest BMIs (p <0.001), DBPs (p <0.001), resting heart rates (p = 0.003), post-PAT heart rates (p = 0.041), SBP (post) (p <0.001), and the lowest aerobic capacity (p = 0.008) and slowest PAT completion times (p <0.001).

3.2. Linear Associations between Demographic Characteristics, Blood Pressure, Heart Rate, Aerobic Capacity and PAT Performance in Firefighters

Table 2 presents the results of univariable and multivariable analyses in relation to the Physical Ability Test. In the univariable models, age demonstrated a significant positive association (β = 3.750, p < 0.001) with physical ability, while weight, diastolic blood pressure, and heart rate post-test showed no significant relationship. The results showed that height, BMI, heart rate, and SBP, both pre and post-test, exhibited significant associations with physical ability (p <0.001, p = 0.003, p <0.001, p <0.001, p <0.001, respectively). In model 2, after adjustment for age and sex, height (p <0.001), heart rate (p = 0.015), and SBP both pre- and post (p <0.001) retained their significant associations with the PAT. In model 3, age, height, SBP (post) and SBP diff. remained significantly associated with PAT completion times (all p <0.001). The results confirm the hypothesis that PAT performance is significantly related to demographic characteristics and measures of cardiovascular health.

3.3. Associations between Demographic Characteristics, Blood Pressure, Heart Rate, Aerobic Capacity and PAT Performance in Firefighters

Table 3 presents the odds ratios of firefighters passing the physical ability test, based on demographic characteristics, resting and recovery blood pressure, and heart rate. Age was found to be significantly associated with the PAT pass rate (OR = 0.96, p < 0.001). Similarly, males were eighteen times more likely to pass the PAT compared to females (OR = 18.41, p <0.001). Firefighters with higher BMIs and higher heart rates were less likely to pass the PAT (p < 0.001). In addition, firefighters with higher SBP differences and higher heart rate differences, pre-and-post-test, were more likely to pass the PAT (both p <0.001). An increase in aerobic capacity was associated with an increase in the odds of passing the PAT (OR = 1.06, p = 0.003). These results confirm our hypothesis that a linear relationship exists between demographic characteristics and cardiovascular measures in firefighters.

3.4. Multivariable Analysis

In model 2 of the multivariable analysis, after adjusting for age and sex, an increase in BMI and heart rate remained associated with lower PAT pass rates in firefighters (p = 0.039, p < 0.001). In addition, a larger difference between SBP and DBP pre-and-post-test was associated with a higher likelihood of passing the PAT (p <0.001, p = 0.014). After adjustment, an increase in aerobic capacity remained significantly associated with an increase in odds of passing the PAT (OR = 1.05, p = 0.023). In model 3, age (OR = 0.92), sex (OR = 28.56), heart rate (OR = 0.91), systolic blood pressure (post) (OR = 1.02), and SBP difference (OR = 1.10) remained significantly associated with PAT pass rates. The hypothesis remained true after adjustment for age, sex and aerobic capacity.

3.5. Associations between Demographic Characteristics, Blood Pressure, Heart Rate, Aerobic Capacity and Individual Task Performance in Firefighters

Table 4 presents the association and odds ratios for passing the individual PAT tasks, based on demographic characteristics, resting and recovery blood pressure, and heart rate, as well as aerobic capacity, in firefighters. Univariable analysis showed that age decreased the odds of passing the SU (OR = 0.91), EC (OR = 0.94), LRE (OR = 0.95), and RD tasks (OR = 0.94). An increase in heart rate decreased the odds of passing the CHDP (OR = 0.95), FE (OR = 0.96), EC (OR = 0.96), LRE (OR = 0.96), and the RD (OR = 0.95) tasks. An increase in heart rate post-PAT was significantly associated with the SU (OR = 1.04), FE (OR = 1.03), EC (OR = 1.03), LRE (OR = 1.03) and RD (OR = 1.03) tasks. An increase in the heart rate difference was significantly associated with the CHDP (OR = 1.04), FE (OR = 1.04), EC (OR = 1.05), LRE (OR = 1.04) and RD (OR = 1.04) tasks. The results of the logistic regression confirmed the hypothesis, showing that resting and post-PAT heart rates and blood pressures were significantly associated with performance on each individual PAT task.

3.6. Multivariable Analysis

In the multivariable analysis, after adjusting for age and sex, an increase in age remained significantly associated with a decrease in the odds of passing the SU (OR = 0.85), EC (OR = 0.93), LRE (OR = 0.94), and RD (OR = 0.94) tasks. After adjustment for covariates, an increase in resting heart rate remained significantly associated with a decrease in odds of firefighters passing the CHDP (OR = 0.96), FE (OR = 0.96), EC (OR = 0.96), LRE (OR = 0.97) and RD (OR = 0.97) tasks. In addition, an increase in heart rate post-PAT was significantly associated with an increased odds of firefighters passing the SU (OR = 1.03), FE (OR = 1.02), EC (OR = 1.03), LRE (OR = 1.03), and RD (OR = 1.03) tasks. In addition, an increase in heart rate difference was associated with increased odds of passing the CHDP (OR = 1.04), FE (OR = 1.04), EC (OR = 1.05), LRE (OR = 1.04), RD (OR = 1.04). The hypothesis remained true after adjusting for covariates, such as age and sex, indicating that resting measures of heart rate and blood pressure as well as post-PAT were significantly associated with PAT task performance.

4.1. Associations between Demographic Characteristics and PAT Performance

In the results of the current study, as firefighters aged, their performance on the PAT decreased significantly. Similarly, Michalides et al. [7] reported that age was negatively correlated with ability test performance in firefighters. Similarly, Williford et al. [22] reported that as firefighters aged, their performance of occupational tasks significantly decreased. This was further corroborated by Ras et al. [17] where the study found that in firefighters from Cape Town, age was negatively correlated with occupational performance. Previous studies have found that aging is associated with a decrease in cardiorespiratory fitness and musculoskeletal health among firefighters [41-43]. In addition, as firefighters age, their likelihood of developing cardiovascular disease increases significantly [6, 44, 45]. The combination of reduced cardiorespiratory fitness and musculoskeletal health, as well as a reduction in cardiovascular health, may explain the poorer performance on the PAT. In addition, males were significantly more likely to pass the PAT compared to females, with female completion times nearly double those of males (675.7 seconds vs 377.1 seconds). This is supported in previous studies, where it has been well established that female firefighters’ tended to fare worse on the occupational performance assessments, compared to male firefighters [3, 17, 46]. Males have been shown to have a higher muscle mass, and bone mineral density and are able to produce higher force compared to females [46-48], providing a possible explanation for the difference in results. In addition, males were found to be taller and heavier than females, which is significantly correlated with task performance in firefighters [17, 18, 22]. Furthermore, a meta-analysis conducted by Nuzzo [49] indicated that men tended to have much greater cross-sectional area and greater distribution of Type II fibres compared to females, which accounts for much of the strength disparities between males and females. This may provide an additional reason for the sex disparities, as the PAT is very strength and anaerobic power dominant [17, 50].

Height was a significant factor in firefighters passing the PAT, where significant inverse associations were present between height and PAT completion times, which remained significant after adjustment for age, sex and aerobic capacity in firefighters. Phillips et al. [40] reported similar results, where the authors found that taller and heavier firefighters tended to perform better on simulated firefighting tasks compared to shorter firefighters and those who weighed less. In addition, the results of the current study showed that heavier firefighters were less likely to pass the step-up task, which is similar to the results reported by Phillips et al. Phillips et al. [40] noted that heavier firefighters had an advantage over tasks that required heavy lifting and force production but performed worse on tasks that required them to support their body weight while carrying additional loads. These results were supported by previous studies that height may be advantageous in performing many tasks, particularly those that require firefighters to lift objects and apply high amounts of force, such as a ladder raise and extension and rescue drag [7, 22, 51]. The current study reported that BMI was significantly associated with decreased PAT performance. Previous literature supports these results, as it has been consistently shown that firefighters with higher BMIs, particularly those over 30 kg•m-2 performed significantly worse on firefighter ability tests [7, 18, 20, 52].

4.2. Associations between Heart Rate and PAT Performance

The current results showed that heart rate, heart rate post-PAT, and pre-and-post-PAT differences were significantly related to PAT performance. Similarly, studies by Michaelides et al. [7, 20] reported that heart rate was inversely associated with ability test performance in firefighters. This was supported by Williams et al. [53] Those who did not finish the candidate physical ability test reported a higher heart rate than those who completed it. Similarly, Davis et al. [54] found that maximal heart rate was significantly associated with performance on simulated firefighting tasks. Firefighters with a lower resting heart rate, theoretically, would have a higher heart rate reserve and be able to achieve a higher increase in heart rate while performing the PAT [23, 25, 55]. Adaptations to exercise, as one increases their aerobic capacity, is a decrease in resting heart rates [56, 57]. If firefighters perform the PAT at their maximum capacity, their heart rates would increase exponentially, particularly if they attempt to complete the PAT as quickly as possible [7, 18, 20]. In addition, in those firefighters with higher resting blood pressures and heart rates, there would be a concomitant increase in heart rates during the PAT, which may remain elevated well after completion of the PAT [31, 58-60]. This would result in a lower cardiac output and higher heart rates during the PAT [61, 62], resulting in firefighters reaching exertional fatigue earlier [17, 58, 61-63], leading to poorer performance. Moreover, this poses a significant risk to firefighters, potentially leading to sudden cardiac events.1 This could provide a possible explanation for the linear association between PAT completion times and a larger heart rate difference.

4.3. Associations between Blood Pressure and PAT Performance

Systolic blood pressure, pre-and-post-PAT, and the difference between pre-and-post-PAT blood pressure readings were significantly associated with PAT completion times and pass rates. A study by Rynne et al. [64] reported that firefighters who had hypertension had higher blood pressure responses than firefighters who were normotensive. In the current study, the mean blood pressure post-PAT was 163.1 mm Hg, compared to Rynne et al.64 where blood pressures ranged between 135.9 and 141.9 mm Hg. The exaggerated difference between the two studies may be explained by the firefighters in the current study having higher resting blood pressures, which may explain the exaggerated post-PAT blood pressures. Blood pressures have been shown to increase linearly with heart rate and exercise intensities [65, 66]. Less fit firefighters, or those with higher resting blood pressures, may cause them to reach a point where their mean arterial pressure starts to reduce cardiac output [16, 58, 67]. Moreover, the association between the difference between pre-and-post-PAT blood pressures and PAT performance may be explained by the blood pressure “reserve” in normotensive firefighters before the afterload starts to reduce cardiorespiratory functioning [67-69]. Previous studies have shown that the stress related to firefighters and the constant exposure to toxic chemicals and fumes may be important factors accounting for arterial dysfunction, which ultimately leads to an increase in blood pressure and dysfunctional blood pressure regulation [16, 64, 70]. The exaggerated blood pressure responses may result in, not only reduced work capacity, but also lead to adverse cardiovascular events [10]. The results indicated that blood pressure, pre-and-post-PAT remained significantly associated with PAT performance after adjustment for aerobic capacity. This suggests that, regardless of the firefighters' cardiorespiratory fitness and muscles' ability to utilize oxygen, the increased blood pressure as a result of physical exertion, may independently reduce cardiac output and work capacity [16, 67]. Stress has been linked to increased blood pressure [71, 72]. Firefighting is a strenuous occupation that often leads firefighters to develop blood pressure abnormalities [5, 72-74]. Stress and blood pressure may need to be monitored as this may negatively impact work capacity, regardless of overall physical fitness levels.

4.4. Associations between Aerobic Capacity and PAT Performance

In the present study, aerobic capacity was significantly associated with PAT completion times and overall PAT pass rates in firefighters. Similarly, studies conducted by Skinner et al. [52] and Sheaff et al. [75] reported that V̇O2max was significantly and inversely associated with ability test/work performance tests in completion times. Fitter firefighters may be able to sustain a higher level of intensity for longer during the PAT, explaining the association present in the current study. Fitter firefighters would likely have lower resting and exercise blood pressure levels, suggesting that firefighters with lower blood pressures may be fitter. Interestingly, in the present study, aerobic capacity was not associated with pass rates for individual tasks. Previous studies have suggested that overall muscular strength and endurance may play a larger role in completing specific tasks, rather than aerobic capacity. [17, 18, 51,22] Firefighters who have a higher aerobic capacity may have a lower body mass, which has been shown to disadvantage firefighters when completing individual tasks [40, 76]. The current study used a calculation that estimated V̇O2max, which may be less accurate for older adults [37, 57]. This may have influenced the results slightly, and should be kept in mind when interpreting the findings.

4.5. Factors Affecting Individual Task Performance

For the SU task, younger, lighter males with higher post-PAT heart rates and a larger SBP difference were more likely to pass the step-up task. This is a similar result found by Phillips et al. [40], who reported that tasks incorporating moving their own body weight and additional load, such as the stair climb or SU task, their performance decreased. In addition, older firefighters may have sustained lower limb injuries or musculoskeletal discomfort which may influence their performance on this task [17, 77]. Moreover, the SU task, due to its anaerobic nature [78], would cause significant increases in blood pressure. Firefighters with lower blood pressure may tolerate a larger increase in blood pressure before significant fatigue sets in.16,58 A similar result was shown in the CHDP task, where firefighters who had lower resting heart rates, larger heart rate differences, and higher aerobic capacity were more likely to pass. Similar, studies by Michaelides et al. [7, 20] have shown that firefighters with lower resting heart rates were more likely to pass the hose drag task. In addition, a lower resting blood pressure will result in a higher cardiac output as peripheral resistance remains lower [58, 66]. In addition, the CHDP is the most strenuous of the tasks causing the highest physical stressors, which higher blood pressures may accentuate, leading to premature fatigue and lower work rates [17, 50]. It was found that males who had a lower heart rate and larger heart rate difference were more likely to pass the FE task. The FE task is an upper extremity-dominated task, where higher force production would equate to quicker task completion [50, 79]. Research has shown that females tend to have significantly lower upper-body muscular and force production compared to males, possibly explaining the performance bias toward males [46-48]. For the EC, younger males with a lower resting heart rate, higher heart rate difference, and higher aerobic capacity were more likely to pass. In addition, for the LRE and RD tasks, younger firefighters with lower resting heart rates and larger heart rate differences were more likely to pass. Similar to the FE task, the EC required firefighters to carry 25kg drums 50 meters. Insufficient grip strength would lead to poorer performance. Research has indicated that males tended to have higher grip strength compared to female firefighters, explaining males' better performance [17, 50]. In addition, there may have been a fatigue carryover to early onset of cardiovascular and muscular exhaustion in firefighters who had higher blood pressure and heart rates [50, 79, 80], as the 20-second recovery between each task would be insufficient [81, 82]. Possibly, firefighters who had lower resting blood pressures and heart rates had higher cardiorespiratory fitness levels and were less likely to have experienced significant fatigue prematurely during the PAT. The outcome of the study suggests that blood pressure and heart rate play an important role in the workability and efficiency of firefighters beyond the assumption that it may potentially lead to cardiovascular incidents on-duty.

4.6. Strengths and Limitations

A strength of the study was the relatively large sample size, which strengthened the results that were drawn from the dataset. This was the first study conducted on firefighters from the CoCTFRS that investigated the association between physical ability test performance and blood pressure and heart rate pre-and-post-PAT. However, there were several limitations of the study. The first limitation was that this was a secondary data analysis, which could influence the validity of the results. Secondly, female firefighters made up a very small proportion of participants in the current study, which may limit the generalizability of the results to this population. Thirdly, there were instances of missing data in the datasheet, and these firefighters were excluded from the analysis. A fourth limitation would be that healthier and fitter firefighters may have been more likely to complete the PAT. Lastly, aerobic capacity was estimated using a non-exercise calculation, which may not have been a true reflection of the firefighters' aerobic fitness levels, especially since this calculation takes age into account and may have biased the results in favor of younger firefighters.