Firefighter Cardiorespiratory Fitness (CRF) Pilot Study

Firefighters are exposed to extreme metabolic and cardiopulmonary stressors in the
performance of their vocation that are recognized to exceed the actual physical or
environmental hazards. The current medical literature regarding firefighting highlights two
frequently cited statistics: (1) based on body mass index (BMI), upwards of 73-80% of
firefighters are considered overweight or obese, and (2) >45% of firefighter line-of-duty
deaths are due to cardiovascular events.

This finding regarding BMI has been widely reported in the U.S. media after being published
in a 2014 CDC medical journal. Such a finding is particularly relevant to firefighters given
that there are recommended cardiorespiratory performance standards for firefighters, commonly
12 metabolic equivalents (METs) or maximum oxygen consumption during aerobic exercise
(VO2max) of 42 mL O2/kg of body weight/min. As a consequence, failure to meet such a standard
may limit a firefighter's ability to perform (or be employed) in full-duty tasks based on
individual fire station requirements.

Fire suppression activities account for 1-5% of a firefighter's duty time yet result in 32%
of firefighter deaths. This is attributable to the extreme physical demands of firefighting
activities in which anaerobic threshold (typically 85% of maximal heart rate) may be exceeded
and sustained throughout an engagement. Few professions, other than elite athletes, require
this level of cardiorespiratory fitness (CRF). As such, CRF is of vital importance to
firefighters and yet is rarely, if ever, tested in a systematic fashion over the course of an
individual firefighter's career.

The vital importance of CRF is well-established in the medical literature. Epidemiological
studies have demonstrated an inverse relationship between CRF and coronary heart disease
(CHD) and all-cause mortality in healthy individuals. There are incremental health benefits
to increased levels of fitness and reduced morbidity and mortality associated with lower
levels of fitness. The fitness standard of 12 METs (the equivalent of a VO2max of 42
mL/kg/min) remains the testing metric for firefighters in the NFPA 1582 guidelines; it is
applied to all candidates, male or female, and of any age. While a VO2max of 42 may be "good"
to "excellent" for a 50-59 year old male, it is only "good" for a 40-49 year old male, and
only "fair" for a 30-39 or "poor" for a 20-29 year old male. In women, a VO2max of 42
indicates a "good" level of CRF for a 20-29 year old female and "superior" CRF for a 50-59
year old female. Knowing that CRF declines inevitably with age argues that a firefighter
whose VO2max is 42 mL/kg/min at age 20 will decline significantly by age 50 and raises the
question of their ability to safely participate in fire suppression activities at that age.
CRF measures in firefighters would benefit from age-adjustment and gender stratification.
This research would begin that process.

While elevated BMI is associated with cardiovascular disease morbidity and mortality, BMI has
been demonstrated to be a non-specific metric of body composition. Specifically, BMI "is
limited as an index of obesity (body fatness) because it does not account for the composition
of body weight," and the concurrence of BMI and body fat percentage (BF%) is affected by age,
gender, ethnicity, and body shape. The misclassification of firefighters as overweight and
obese based on BMI has been discussed in a several studies. These studies utilized
bioimpedance testing or skin calipers for BF% measurement, methods known to have significant
levels of error in terms of false positives and false negatives. Interestingly, a series of
these studies cite a single article with a sample size of 39 individuals as validation of
bioimpedance in comparison to dual-energy X-ray absorption (DXA), but also report DXA as the
gold standard for BF% measurement. This inaccuracy of BF% compared to BMI was addressed
thoroughly in one study of U.S. firefighters, demonstrating the potential for false positive
and false negative identification of obesity in this population; specifically, they reported
rates of 15.4% false positive and 18.2% false negative identification of obesity when
identified by BMI as opposed to BF%.

The primary advantages of using BMI in a clinical setting include the long-established
history of BMI usage and its extremely low cost (simply measuring someone's height and
weight). However, waist circumference (WC) is easily measured, and has demonstrated
comparable prediction of cardiovascular risk as compared to and in conjunction with BMI.10
Although classification of obesity has not been conducted by WC, an elevated cardiovascular
risk has been identified for men with WC > 102 cm and women with WC > 88 cm.More
specifically, WC classifications of very low, low, high, and very high have been developed.
For purposes of this study, WC measurements within the high and very high classifications are
considered as obese, with this population (WC > 100 cm in males, WC > 90 cm in females)
representing a similar population to those identified with an increased cardiovascular risk.

The knowledge gap between BF% and cardiovascular risk as it pertains to clinical use of BMI
and other body composition metrics has been identified by the National Heart, Lung, and Blood
Institute (NHLBI), whose 2013 systematic review noted, "studies using BMI and waist
circumference compared to more valid measures of percent body fat are needed to examine the
predictive role of various adiposity measures." However, strong correlations between body
composition metrics and CRF were found in a recent study in Brazilian firefighters, and in
this case, BMI was considered to be an adequate surrogate for other body composition methods
evaluating body composition. A limitation of this study was that it used skin caliper testing
for BF% measurement and a non-respiratory-based exercise test to indirectly estimate VO2max.
Thus, there is an evident need to clarify which among several potential measures of body
composition best predicts CRF, with firefighters serving as a relevant population for study.
To the best of our knowledge, there are no studies that utilize the accepted criterion
standard of dual X-ray energy absorption (DXA) scanning coupled with measured VO2max testing
that would allow coupling these two metrics into a reference fitness-leanness measure.

DXA is a widely-available technology that is relatively inexpensive compared with other
diagnostic technologies, is safe, and can accurately measure BF%. DXA studies can be
completed in less than ten minutes and provide data that is valid and reproducible over time.
The radiation from a DXA scan is less than that received from routine environmental exposure
in a single day. Americans typically receive approximately 3.0 milliSieverts (mSv) of
radiation exposure annually from cosmic radiation, household radon, and other environmental
sources. This does not include elective diagnostic imaging sources. The radiation exposure of
a DXA scan is ~0.005 mSv, about a tenth of that from a single chest x-ray (CXR). 19 By
comparison a CT scan of the pelvis, chest or abdomen can expose the patient to 6.0 -10.0 mSv
in one study (the equivalent of 2-3 years of environmental exposure in a single medical
study). A CT scan of the head is ~2.0 mSv.20 A lumbar spine X-ray series is ~1.5 mSv and a
single PA (posterior-anterior) chest X-ray (CXR) is ~0.06 mSv. The precept of As Low As
Reasonably Achievable (ALARA) in order to minimize radiation exposure is easily honored in
the case of DXA scanning due to the extremely low mSv exposures. The Biological Effects of
Ionizing Radiation (BEIR) VII report and executive summary provide definitive recommendations
regarding radiation exposure and cancer risk.

DXA has been identified an accurate method of measuring BF%, with the additional benefit of
also measuring lean body mass percentage (LBM%) and, of course, bone mineral density (BMD),
as well. This is supported by numerous studies including BF% measured by DXA as the reference
against their study variable of interest. Obesity has been defined for BF% by age categories,
with classifications of low, mid, high, and obesity, where the bottom of the low range is the
minimum of essential body fat. On the other hand, LBM% has not been extensively studied in
correlation with obesity in adults, though contemporary work has been conducted to estimate
LBM% in children and adolescents.

As such, this study aims to address which body composition methods best correlate with CRF in
firefighters. Investigators hypothesize that BF% will better correlate with CRF metrics than
traditional (but technologically outdated) body composition methods, such as BMI or waist
circumference (WC), and furthermore in conjunction with measurement of LBM%. Additionally,
investigators hypothesize that these data, in conjunction with demographic, employment,
physical activity, and medical history data, can comprise a simplified metric (a
cardiorespiratory risk score) to estimate firefighter CRF. In this context, a cost analysis
of the evaluated surveillance methods will be generated.

Results of this analysis will provide pilot data and inform future work to assess whether
providing more accurate data on body composition can lead to more effective reductions in
cardiorespiratory risk in this population. This study has the additional benefit of creating
the availability of DXA three-compartment (fat mass, lean mass, bone mineral content) body
composition at our institution, where this study is not currently performed despite the
required technology already being used for bone studies.

Inclusion Criteria:

1. Fire fighter from selected local metropolitan fire department(s)

2. Willing and agree to complete all data collection components of the study -
Anthropometrics, participant survey, Concept 2 Rower Test 2,000 meter test, Treadmill
VO2max Test, and DXA scan

Exclusion Criteria:

1. Declined participation in the study

2. Unwilling or do not agree to complete all data collection components of the study

3. Pregnant females or females who anticipate being pregnant during the course of the
study due to administration of the VO2max fitness test and DXA scan (pregnancy may not
appropriately reflect an active-duty firefighter's cardiorespiratory fitness and
radiation exposure will be avoided in pregnant individuals)

4. Those who are not currently authorized to operate at full duty with their fire
department without restrictions