Validation of the firefighter WFI treadmill protocol for predicting VO2 max

Validity of submaximal aerobic capacity and strength tests in firefighters

BACKGROUND

Typically, the fitness of UK firefighters is assessed via submaximal estimate methods due to the low demands on time, money, expertise and equipment. However, the firefighter-specific validity of such testing in relation to maximum aerobic capacity (V˙O2max) and particularly muscular strength is not well established.

AIMS

To examine the validity of submaximal methods to estimate V˙O2max and maximal strength in operational firefighters.

METHODS

Twenty-two full-time operational firefighters (3 female) completed same-day submaximal (Chester Step Test; CST) and maximal (treadmill) assessments of V˙O2max, with a sub-sample of 10 firefighters (1 female) also completing submaximal and maximal back-squat (i.e. one repetition maximum; 1RM) assessments. All participants then completed the Firefighter Simulation Test (FFST) within 2-4 days.

RESULTS

CST underestimated actual V˙O2max by 1.4 ml·kg-1·min-1 (~3%), although V˙O2max values were positively correlated (r = 0.61, P < 0.01) and not significantly different. Estimated V˙O2max values negatively correlated with FFST performance (r = -0.42). Predicted 1RM underestimated actual 1RM by ~2%, although these values were significantly correlated (r = 0.99, P < 0.001) and did not significantly differ. The strongest predictive model of FFST performance included age, body mass index, and direct maximal measures of 1RM and V˙O2max.

CONCLUSIONS

Submaximal back-squat testing offers good validity in estimating maximum firefighter strength without exposure to the fatigue associated with maximal methods. The CST provides a reasonably valid and cost-effective V˙O2max estimate which translates to firefighting task performance, although the error observed means it should be used cautiously when making operational decisions related to V˙O2max benchmarks.

Firefighter Health: A Narrative Review of Occupational Threats and Countermeasures

Structural firefighters are responsible for protecting properties and saving lives during emergency operations. Despite efforts to prepare firefighters for these hazardous occupational demands, the unfortunate reality is that the incidence of health morbidities is increasing within the fire service. Specifically, cardiovascular disease, cancer, and mental health disorders are among the most documented morbidities in firefighters. Pubmed and Google Scholar search engines were used to identify peer-reviewed English language manuscripts that evaluated firefighters' occupational health threats, allostatic factors associated with their occurrence, and evidence-based strategies to mitigate their impact. This narrative review provides fire departments, practitioners, and researchers with evidence-based practices to enhance firefighters' health.

Influence of Cardiorespiratory Fitness on Cardiac Autonomic Recovery Among Active-Duty Firefighters

Cornell, DJ, Flees, RJ, Shemelya, CM, and Ebersole, KT. Influence of cardiorespiratory fitness on cardiac autonomic recovery among active-duty firefighters. J Strength Cond Res 38(1): 66–73, 2024—It has been suggested that an inability of the autonomic nervous system (ANS) to recover after strenuous events is a potential cause of sudden cardiac death among firefighters. The purpose of this study was to examine the influence of cardiorespiratory fitness (CRF) on the heart rate recovery (HRR) kinetics of firefighters. Thirty-seven male career active-duty firefighters completed both a submaximal step test and a maximal treadmill graded exercise test. A monoexponential curve was fit to postexercise submaximal and maximal HRR data of each subject. Subjects were placed into Low CRF (n = 13) and High CRF (n = 24) groups based on the standard peak aerobic capacity (V̇O2peak) criterion of <42 ml·kg−1·minute−1 and ≥42 ml·kg−1·minute−1, respectively. After controlling for age and body mass index, CRF was significantly (p < 0.05) correlated with the decay rate ( ) and asymptote ( ) after submaximal exercise (r sp = −0.556; r sp = −0.637, respectively), as well as the , , and amplitude ( ) after maximal exercise (r sp = −0.353; r sp = −0.416; r sp = 0.603, respectively). High CRF firefighters demonstrated a significantly faster after both submaximal (p = 0.003) and maximal exercise (p = 0.043), a lower after submaximal exercise (p = 0.002), and a higher after maximal exercise (p = 0.001), than Low CRF firefighters. Greater CRF was associated with enhanced HRR kinetics after submaximal and maximal exertion, suggesting that CRF may positively influence the ANS recovery of firefighters.

Performing one or more verification VO2 workload(s) immediately after an incremental to maximal graded exercise test significantly increases the proportion of participants who meet the job-related aerobic fitness standard for structural firefighters

PURPOSE

Graded exercise tests (GXTs) are commonly used to determine the maximal oxygen consumption (VO2max) of firefighter applicants. However, the criteria used to confirm VO2max are inconsistent and have a high inter-subject variability, which can compromise the reliability of the results. To address this, a verification phase (VP) after the GXT has been proposed as a "gold standard" protocol for measuring VO2max.

METHODS

4179 male and 283 female firefighter applicants completed a GXT and a VP to measure their VO2max. VO2peak values measured during the GXT were compared to the VO2 values measured during the VP. The proportion of participants who met the job-related aerobic fitness standard during the GXT was compared to that of those who met the required standard during the VP.

RESULTS

For male and female participants that required the VP to attain their VO2max, the VO2peak values measured during the GXT (47.3 ± 6.0 and 41.6 ± 5.3 mL kg-1 min-1) were, respectively, 10.1% and 10.3% lower than the VO2 values measured during the VP (52.1 ± 6.7 and 45.9 ± 6.4 mL kg-1 min-1), p < 0.001. Furthermore, the proportion of male and female participants who met the job-related aerobic fitness standard significantly increased from the GXT to the VP by 11.6% and 29.9%, respectively, p < 0.001.

CONCLUSION

These results strongly support the use of a VP to confirm VO2max, especially for females, older and overweight individuals. These findings are applicable to other physically demanding public safety occupations and when examining the efficacy of training interventions on VO2max.

The Acute Effect of High-Intensity Resistance Training on Subsequent Firefighter Performance

ABSTRACT

Mason, MR, Heebner, NR, Abt, JP, Bergstrom, HC, Shapiro, R, Langford, EL, and Abel, MG. The acute effect of high-intensity resistance training on subsequent firefighter performance. J Strength Cond Res 37(7): 1507-1514, 2023-High-intensity resistance training (HIRT) is commonly performed by structural firefighters on duty to enhance occupational readiness. However, exercise-induced fatigue may negatively impact subsequent occupational performance. Therefore, the purpose of this study was to assess the acute effect of HIRT on subsequent occupational physical ability in structural firefighters and to determine the time course of recovery. Seven resistance-trained male firefighters performed a timed maximal effort simulated fireground test (SFGT) in 3 randomized conditions: baseline (SFGT baseline ), 10 minutes post HIRT (SFGT 10min ), and 60 minutes post HIRT (SFGT 60min ). Work efficiency and air depletion were assessed during the SFGT. The timed HIRT session consisted of a standardized set of exercises using absolute training loads. Repeated measures analysis of variance and minimal difference (MD) analysis assessed group and individual effects between the conditions, respectively. The level of significance was set at p < 0.05. SFGT 10min completion time was greater than SFGT baseline (430 ± 137 vs. 297 ± 69 seconds, p < 0.01), with no difference between SFGT baseline and SFGT 60min (297 ± 69 vs. 326 ± 89 seconds, p = 0.08). The MD analysis indicated that all firefighters' SFGT 10min times exceeded the MD (±26.4 seconds) compared with SFGT baseline . However, 43% of firefighters still exceeded the MD at SFGT 60min . Air depletion during SFGT 10min was greater than that during SFGT baseline (2,786 ± 488 vs. 2,186 ± 276 lb·in -2 , p = 0.02), with no difference between SFGT baseline and SFGT 60min ( p = 0.25). Work efficiency during SFGT 10min was 40% lower than that during SFGT baseline ( p < 0.01), with no difference between SFGT baseline and SFGT 60min ( p = 0.25). These findings indicate that an acute bout of HIRT decreases multiple descriptors of firefighters' occupational performance 10 minutes post exercise with varied responses at 60 minutes post exercise.

Body Composition Is Related to Maximal Effort Treadmill Test Time in Firefighters

Firefighting tasks may require near maximal levels of cardiorespiratory fitness. Previous research has indicated that body fat percentage (BF%) and aerobic capacity (VO_2peak) are related to the performance of firefighting tasks. Since a standard submaximal treadmill test for firefighters is terminated at 85% of maximal heart rate (MHR), key performance information relating to maximal cardiorespiratory effort may not be measured in a submaximal test. The purpose of this study was to examine the relationships between body composition and time spent running at intensities greater that 85% MHR. Height, weight, body mass index (BMI; kg/m²), BF%, MHR (bpm), VO_2peak (mL/kg/min), predicted VO_2peak (P-VO_2peak; mL/kg/min), submaximal treadmill test time (WFI_sub Test Time; min), and maximal treadmill test time (WFI_max Test Time; min) were collected in fifteen active-duty firefighters. The results indicated that significant relationships (p < 0.05) existed between BF% and VO_2peak, BF% and WFI_max Test Time, BF% and T_diff, and VO_2peak and WFI_max Test Time. P-VO_2peak was not significantly different than VO_2peak, and the WFI_max Test Time was significantly longer than the WFI_sub Test Time. These results indicate that a submaximal treadmill test may reasonably predict VO_2peak, but key information about physiological work at intensities greater than 85% MHR may be missed when using submaximal effort tests.

Customized Occupational-Specific Graded Exercise Test for Structural Firefighters: An Update

OBJECTIVE

The aim of the study is to validate a customized V˙O 2max Graded Exercise Test (GXT) protocol specifically to accommodate firefighters with different cardiovascular fitness levels.

METHODS

Career male firefighters (N = 15) completed 3 customized GXTs on a treadmill: 1 in athletic clothes and 2 in their bunker gear to determine maximal oxygen uptake (V˙O 2max ).

RESULTS

The on-duty task protocol was reliable, V˙O 2max values of 40.2 ± 4.6 mL·kg·min -1 and 40.3 ± 5.3 mL·kg·min -1 between trials yielded an interclass correlation of 0.911 with a typical error of 1.48 mL·kg·min -1 and a coefficient of variation of 4.0%. The validity analysis indicated consistent maximal V˙O 2 values for the GXTs yielding mean interclass correlation of 0.94 with typical error of 1.16 mL·kg·min -1 and a coefficient of variation of 2.9%.

CONCLUSIONS

The customized GXT for structural firefighters has shown to be a reliable, valid, and applicable method of testing cardiovascular fitness in firefighters.

Relationship between a Maximum Plank Assessment and Fitness, Health Behaviors, and Moods in Tactical Athletes: An Exploratory Study

A maximum plank hold (PH) has been implemented in the Army Combat Fitness Test (ACFT) with the Holistic Health and Fitness (H2F) program. The H2F program introduces a shift in wellbeing from a fitness centered approach to framework also comprising nutrition, sleep, mental, and spiritual components. The purpose was to analyze how a maximum PH correlated with fitness, lifestyle behaviors, and mood states in tactical athletes (TA) and assess differences between those who pass and fail. Forty-nine TA completed fitness testing, lifestyle behavior, and mood state surveys. Bivariate correlations were used to examine relationships with PH performance. PH time was significantly correlated with total body mass, fat mass, BMI, push-ups, and state physical energy (SPE). VO_2max was significantly different between the groups who passed and failed the PH. PH was not associated with lifestyle behaviors or trait mood states. PH performance could vary day-to-day as it was correlated with SPE. Individuals with poorer aerobic fitness and body composition may be at risk for failing the PH.

Comparing Physical Fitness in Career vs. Volunteer Firefighters

ABSTRACT

Morris, CE, Arnett, SW, and Winchester, LJ. Comparing physical fitness in career vs. volunteer firefighters. J Strength Cond Res 36(5): 1304-1309, 2022-The purpose of this study was to assess the potential similarities and differences in health and physical fitness profiles between career firefighters (CFF) and volunteer firefighters (VFF). The research protocol consisted of a health and physical fitness assessment, testing the 5 components of health-related fitness using previously published and accepted protocols. The subject population consisted of a total of 138 firefighters, including 119 CFF and 19 VFF. Statistical significance was defined as a p level less than 0.05. An independent t test showed evidence of CFF having a significantly higher value/score for the following variables: height (p = 0.034), V̇o2max (p = 0.006), push-ups completed (p = 0.024), and plank time (p < 0.001). Volunteer firefighters had a significantly higher value for the following variables: fat mass (p = 0.002), body fat percentage (p < 0.001), and absolute grip strength (p = 0.029). There were no significant differences between groups for the following variables: age (p = 0.299), body mass (p = 0.166), fat-free mass (p = 0.281), body mass index (p = 0.057), flexibility (p = 0.106), or relative grip strength (p = 0.887). With regard to physical fitness testing, the VFF had a significantly worse fitness profile across a number of variables than the CFF. Practical applications: Despite the financial and commitment status of volunteer firefighting departments, their members perform an equally dangerous and important job as do firefighters of professional/career firefighting departments, and more attention should be directed toward developing the fitness and performance of these firefighters.

The Relationship between VO2max, Power Management, and Increased Running Speed: Towards Gait Pattern Recognition through Clustering Analysis

Triathlon has become increasingly popular in recent years. In this discipline, maximum oxygen consumption (VO₂max) is considered the gold standard for determining competition cardiovascular capacity. However, the emergence of wearable sensors (as Stryd) has drastically changed training and races, allowing for the more precise evaluation of athletes and study of many more potential determining variables. Thus, in order to discover factors associated with improved running efficiency, we studied which variables are correlated with increased speed. We then developed a methodology to identify associated running patterns that could allow each individual athlete to improve their performance. To achieve this, we developed a correlation matrix, implemented regression models, and created a heat map using hierarchical cluster analysis. This highlighted relationships between running patterns in groups of young triathlon athletes and several different variables. Among the most important conclusions, we found that high VO₂max did not seem to be significantly correlated with faster speed. However, faster individuals did have higher power per kg, horizontal power, stride length, and running effectiveness, and lower ground contact time and form power ratio. VO₂max appeared to strongly correlate with power per kg and this seemed to indicate that to run faster, athletes must also correctly manage their power.

Contribution of the Autonomic Nervous System to Recovery in Firefighters

CONTEXT

Sudden cardiac deaths (SCDs) have accounted for nearly half of the line-of-duty deaths among US firefighters over the past 10 years. In 2018, 33% of all SCDs occurred after the end of a fire service call. Researchers have suggested that an imbalance in autonomic nervous system (ANS) regulation of heart rate postcall may interfere with recovery in firefighters.

OBJECTIVE

To use heart-rate recovery (HRR) and heart-rate variability (HRV), 2 noninvasive markers of ANS function, to examine the ANS recovery profiles of firefighters.

DESIGN

Cross-sectional study.

SETTING

Firehouse and research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty-seven male career active-duty firefighters (age = 39 ± 9 years, height = 178.8 ± 5.4 cm, mass = 87.9 ± 11.2 kg).

MAIN OUTCOME MEASURE(S)

Percentage of maximal HR (%MHR) and HRV (natural log of the square root of the mean sum of the squared differences [lnRMSSD]) were collected after both submaximal and maximal exercise protocols during a 10-minute seated recovery. The HRR profiles were examined by calculating the asymptote, amplitude, and decay parameters of the monoexponential HRR curve for each participant.

RESULTS

Differences in HRR parameters after 10 minutes of seated recovery were identified after submaximal versus maximal exercise (P < .001). In addition, although ANS was more suppressed after maximal exercise, HRV indicated incomplete recovery, and regardless of the test, recovery %MHR and lnRMSSD values did not return to pretest %MHR and lnRMSSD values.

CONCLUSIONS

Our results suggest that the ANS contributions to recovery in active-duty firefighters are exercise-intensity specific, and this is likely an important factor when establishing best-practice recovery guidelines.

Cardiorespiratory fitness assessment among firefighters: Is the non-exercise estimate accurate?

BACKGROUND

Minimum cardiorespiratory fitness (CRF) has been recommended for firefighters due to job requirements. Thus, it is important to identify accurate and readily available methods to assess CRF in this population. Non-exercise CRF estimates (NEx-CRF) have been proposed but this approach requires validation in this population.

OBJECTIVE

To evaluate the accuracy of a NEx-CRF, as compared to a field maximum exercise test, among career military firefighters of both genders using a comprehensive agreement analysis.

METHODS

We evaluated the accuracy of a NEx-CRF estimate compared to the Cooper 12 min running test among 702 males and 106 female firefighters.

RESULTS

Cooper and NEx-CRF tests yielded similar CRF in both genders (differences <1.8±4.7 ml/kg-1.min-1; effect size <0.34). However, NEx-CRF underestimated Cooper-derived CRF among the fittest firefighters. NEx-CRF showed moderate to high sensitivity/specificity to detect fit or unfit firefighters (71.9% among men and 100% among women). Among men, the NEx-CRF method correctly identified most firefighters with less than 11 METs or greater than 13 METs, but showed lower precision to discriminate those with CRF between 11-13 METs.

CONCLUSIONS

The NEx-CRF method to estimate firefighters' CRF may be considered as an alternative method when an exercise-based method is not available or may be used to identify those who require more traditional testing (CRF 11-13 METs).

An Occupational-Specific O2max Protocol for Structural Firefighters

OBJECTIVE

The aim of this study was to validate a (Equation is included in full-text article.)O2max protocol designed specifically for the occupational demands of firefighters by incorporating the use of personal protective equipment (PPE).

METHODS

Career firefighters completed a stage-graded exercise test (GXT) with submaximal square-wave verification bout while wearing PPE (pants and boots) to determine (Equation is included in full-text article.)O2max. Using the self-reported Physical Activity-Rating (PA-R) scale and an estimated nonexercise regression equation of (Equation is included in full-text article.)O2max for comparison to measured.

RESULTS

Twenty-eight male, career firefighters performed the GXT and square-wave bout. (Equation is included in full-text article.)O2 values (mean ± SD) from the GXT and the square-wave verification bout were 41.04 ± 6.98 and 39.74 ± 6.42 mL/kg/min, respectively (ICC = 0.98, typical error = 0.96 mL/kg/min, CV = 2.4%).

CONCLUSION

Our data suggest an incremental treadmill protocol that incorporates PPE and square-wave verification as an occupational-specific tool to measure cardiovascular fitness in firefighters.

Association Between Push-up Exercise Capacity and Future Cardiovascular Events Among Active Adult Men

IMPORTANCE

Cardiovascular disease (CVD) remains the leading cause of mortality worldwide. Robust evidence indicates an association of increased physical fitness with a lower risk of CVD events and improved longevity; however, few have studied simple, low-cost measures of functional status.

OBJECTIVE

To evaluate the association between push-up capacity and subsequent CVD event incidence in a cohort of active adult men.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective longitudinal cohort study conducted between January 1, 2000, and December 31, 2010, in 1 outpatient clinics in Indiana of male firefighters aged 18 years or older. Baseline and periodic physical examinations, including tests of push-up capacity and exercise tolerance, were performed between February 2, 2000, and November 12, 2007. Participants were stratified into 5 groups based on number of push-ups completed and were followed up for 10 years. Final statistical analyses were completed on August 11, 2018.

MAIN OUTCOMES AND MEASURES

Cardiovascular disease-related outcomes through 2010 included incident diagnoses of coronary artery disease and other major CVD events. Incidence rate ratios (IRRs) were computed, and logistic regression models were used to model the time to each outcome from baseline, adjusting for age and body mass index (BMI) (calculated as weight in kilograms divided by height in meters squared). Kaplan-Meier estimates for cumulative risk were computed for the push-up categories.

RESULTS

A total of 1562 participants underwent baseline examination, and 1104 with available push-up data were included in the final analyses. Mean (SD) age of the cohort at baseline was 39.6 (9.2) years, and mean (SD) BMI was 28.7 (4.3). During the 10-year follow up, 37 CVD-related outcomes (8601 person-years) were reported in participants with available push-up data. Significant negative associations were found between increasing push-up capacity and CVD events. Participants able to complete more than 40 push-ups were associated with a significantly lower risk of incident CVD event risk compared with those completing fewer than 10 push-ups (IRR, 0.04; 95% CI, 0.01-0.36).

CONCLUSIONS AND RELEVANCE

The findings suggest that higher baseline push-up capacity is associated with a lower incidence of CVD events. Although larger studies in more diverse cohorts are needed, push-up capacity may be a simple, no-cost measure to estimate functional status.