Physiological determinants of the candidate physical ability test in firefighters.

Abstract

The purpose of this study was to examine the relative importance of physiological characteristics during firefighting performance, as assessed by the Candidate Physical Ability Test (CPAT). Subjects included career and volunteer firefighters aged 18-39 (N = 33). Upper- and lower-body strength, muscle endurance, lower body muscle power, body composition analysis, aerobic capacity, anaerobic fitness, and the heart rate (HR) and blood pressure response to stair climbing were assessed to determine the physiological characteristics of the subjects. To quantify firefighting performance, the CPAT was administered by members of the fire service. Absolute and relative mean power during the Wingate anaerobic cycling test (WAnT), relative peak power during the WAnT, and absolute maximal oxygen uptake (VO2max) were significantly higher in those who passed the CPAT (N = 18), compared to those who failed (N = 15; p < 0.01). Mean power during the WAnT, fatigue index during WAnT, absolute VO2max, upper body strength, grip strength, and the HR response to stair climbing were significantly related to CPAT performance time (p < 0.01). Absolute VO2max and anaerobic fatigue resistance during WAnT best predicted CPAT performance (Adj. R2 = 0.817; p < 0.001). Performance on the ceiling breach and pull was the only CPAT task that was not significantly related to the physiological characteristics assessed. Measures of anaerobic and cardiovascular fitness best predict overall CPAT performance, and individual task performance. Remedial programs aimed at improving firefighting performance should target anaerobic and aerobic fitness qualities.

Full text

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ABSTRACT


Title:
PHYSIOLOGICAL DETERMINANTS
OF THE CANDIDATE PHYSICAL
ABILITY TEST IN FIREFIGHTERS

Andrew K. Sheaff, M.A., 2009

Professor Ben F. Hurley,
Department of Kinesiology



Directed By:
The purpose of this study was to examine the relative importance of physiological
characteristics during firefighting performance, as assessed by the Candidate Physical
Ability Test (CPAT). Participants included professional and volunteer firefighters, ages
18-39 (n=33). Muscle strength, muscle endurance, muscle power, body composition,
aerobic capacity, anaerobic fitness, and the cardiovascular response to stairclimbing were
assessed to determine the physiological characteristics of the participants. To quantify
firefighting performance, the CPAT was administered by members of the fire service.
Absolute and relative mean power during Wingate anaerobic cycling test (WAnT),
relative peak power during WAnT, and absolute maximal oxygen uptake (VO2max) were
significantly higher in those who passed the CPAT (n=18), compared to those who failed
(n=15) (P < 0.01). Absolute and relative mean power during WAnT, fatigue index during
WAnT, absolute VO2max, upper body strength, and the heart rate response to
stairclimbing were all significantly related to CPAT performance time (all P < 0.01).
However, absolute VO2max and anaerobic fatigue resistance during WAnT combined
were the best predictors of total CPAT performance (Adj. R2 = 0.817; P < 0.001).

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Performance on the ceiling breach and pull was the only individual CPAT task that could
not be significantly predicted by the physiological characteristics assessed. Rate-pressure
product during the stairclimb was not related to CPAT performance. In conclusion,
measures of anaerobic and aerobic fitness best predict overall CPAT performance, as
well as individual task performance. Remedial programs aimed at improving firefighting
performance should target anaerobic and aerobic fitness qualities.

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PHYSIOLOGICAL DETERMINANTS OF THE CANDIDATE PHYSICAL
ABILITY TEST IN FIREFIGHTERS


Andrew Kirkham Sheaff











Thesis submitted to the Faculty of the Graduate School of the
University of Maryland, College Park, in partial fulfillment
of the requirements for the degree of
Master of Arts
2009

















Advisory Committee:
Professor Ben F. Hurley, Chair
Professor James M. Hagberg
Professor Marc A. Rogers

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© Copyright by
Andrew Kirkham Sheaff
2009

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Table of Contents

Table of Contents................................................................................................................ 1
Introduction......................................................................................................................... 1
Research Hypotheses and Significance .............................................................................. 5
Research Hypotheses...................................................................................................... 5
Significance..................................................................................................................... 5
Methods............................................................................................................................... 6
Subjects........................................................................................................................... 6
Design/Variables............................................................................................................. 6
One-repetition maximum (1-RM) strength..................................................................... 6
Muscle Endurance........................................................................................................... 8
Muscle Power.................................................................................................................. 9
Peak Anaerobic Power, Mean Anaerobic Power, and Fatigue Index........................... 10
Aerobic Capacity .......................................................................................................... 10
Body Composition........................................................................................................ 11
Cardiovascular Responses to Stair-Climbing............................................................... 12
Candidate Physical Abilities Test (CPAT)................................................................... 12
Statistical Analysis........................................................................................................ 14
Results............................................................................................................................... 15
Subjects......................................................................................................................... 16
Muscle Strength, Muscle Power, VO2max, and WAnT............................................... 16
Determinants of Successful CPAT Performance.......................................................... 16
Relationship Between Physical Attributes and CPAT Performance Time................... 17
Relationship between physical attributes and successful CPAT performance............. 18
Determinants of rate-pressure product (RPP)............................................................... 19
Individual task determinants......................................................................................... 19
Discussion......................................................................................................................... 20
Review of Literature......................................................................................................... 28
Cardiovascular Disease in Firefighters......................................................................... 29
Occupational Risk Factors............................................................................................ 33
Physiological Responses to Fighting Fires................................................................... 34
Metabolic Responses................................................................................................. 36
Endocrine Responses................................................................................................ 39
Fitness Characteristics of Firefighters .......................................................................... 40
Fitness and Job Performance ........................................................................................ 43
Needs for Future Research............................................................................................ 46
Appendix A- Delimitations & Limitations....................................................................... 48
Delimitations................................................................................................................. 49
Limitations.................................................................................................................... 49
Appendix B- Tables.......................................................................................................... 49
Appendix C- Figures......................................................................................................... 51
Appendix D- Raw Data..................................................................................................... 54
References......................................................................................................................... 58
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Introduction

The physical demands of firefighting, as an occupation, are characterized by
significant activation of the cardiovascular, metabolic, and endocrine systems. Heart
rates in excess of 95% of maximum (53, 55, 72, 74, 89, 92), rates of oxygen consumption
approaching maximal oxygen uptake (VO2max) (10, 34, 89, 92), and significant
activation of the sympathoadrenal axis (64, 76) have been recorded during simulated or
live firefighting tasks. Thus, fire fighting suppression activities may be a significant
physiological stress and high levels of fitness are required by the firefighter. Although
the generalized physiological reactions to fighting fires have been investigated, the
physical attributes and fitness components required for optimal firefighting performance
have not been fully identified. For this reason, it has been difficult to design appropriate
remedial intervention programs that make optimal improvements in the qualities most
important for firefighting performance. Previous studies on firefighters have assessed
factors most closely aligned with steady state work/exercise, i.e., aerobic metabolism (10,
23, 25, 66, 74, 89), while little is known about the role of anaerobic energy sources
during firefighting tasks (92).
Several studies have correlated physical attributes with performance in individual
firefighting-related tasks (16, 65, 89, 93). In these studies, muscle strength (65, 89, 93),
body composition (93), absolute VO2max (89), and muscle endurance (65, 93) are
significantly related to task performance. Cardiovascular fitness predicted performance
in one study (93), but failed to do so in another (65), raising questions as to the relative
importance of cardiovascular fitness for firefighting performance. Stairclimbing tasks in
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full gear have been shown to elicit heart rates of 95% of maximum and rates of oxygen
consumption equivalent to 80 % of VO2max (61).
Intense muscular exertions in firefighters with compromised cardiovascular systems
can precipitate cardiac events when the heart’s demand for oxygen (myocardial oxygen
demand) exceeds its oxygen supply capabilities. The product of heart rate and systolic
blood pressure (RPP) offers a reliable index of myocardial oxygen demand and serves as
an indicator of the cardiovascular and metabolic stress placed on the heart during
strenuous activity. Reducing the RPP response to firefighting tasks may reduce the risk
of a cardiac event in predisposed firefighters, by lowering the cardiovascular and
metabolic stress on the heart during the task. However, no information is available on the
fitness and body composition components that are most closely associated with a low
RPP response to firefighting tasks.
While most studies have examined the dynamics of heart rate and oxygen uptake
during firefighting performance, some have observed substantial elevations in peak
lactate values (34, 89), as well as varying oxygen demands (34), elevated respiratory
exchange ratios (92), and heart rates (23, 67) among different tasks. Coupled with the
inherently unpredictable nature of emergency situations, the data suggest that firefighting
is an intermittent, non-steady state activity. Despite the apparent importance of anaerobic
fitness, limited research has been done to clarify the relationship between muscular
power and firefighting performance. One study examined the importance of muscular
power, as measured by the standing long jump, to firefighting tasks (16). More recently,
another study found a moderate relationship between peak power during WAnT and
firefighting performance (92). Anaerobic endurance, as measured by 400m run, was also
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reported to be positively related to firefighting task performance (65). Thus, there is a
need to clarify the relative influence of aerobic versus anaerobic fitness to firefighting
performance.
Few studies have examined the relationship between fitness and integrated
firefighting tasks. In this context, the Candidate Physical Ability Test (CPAT) is a
nationally established firefighting simulation test, which is currently employed by many
fire departments throughout the country to screen applicants. Yet, information is lacking
on the relative contribution of the various physical or functional attributes that determine
optimal CPAT performance.
Characterization of the physiological variables contributing to CPAT performance
can potentially improve the application process. The establishment of the minimal
physical capacities necessary to successfully complete CPAT can potentially result in
significant financial savings through an improved screening process (11). Additionally,
by further clarifying the physiological determinants of CPAT performance, the fitness
requirements for optimal firefighting performance can be established and applied to
create training programs capable of improving CPAT, and ultimately, improving
firefighting performance.
Williams-Bell et al. (92) recently reported on the physiological demands of CPAT
through the use of portable metabolic analysis. Respiratory exchange ratios in excess of
1.0 were demonstrated during CPAT, suggesting significant activation of anaerobic
metabolism. Absolute VO2max during treadmill running was able to explain 57% of the
variation in CPAT performance. However, the subjects studied were not firefighters,
order and fatigue effects were not controlled, body composition was not measured, and
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only indirect assessments of muscular strength were implemented in this investigation.
Consequently, there is a need to further examine these parameters in firefighters while
attempting to control for the influence of fatigue on sensitive such, such as strength,
power, and anaerobic capacity.
Therefore, the purpose of this study was to examine the relative importance of
several physiological variables during CPAT performance in active firefighters, while
controlling for order and fatigue effects of testing. Because of the intermittent nature of
fighting fires, it is hypothesized that physical attributes, such as muscular strength,
power, and anaerobic power are better predictors of CPAT performance than aerobic
capacity.













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Research Hypotheses and Significance

Research Hypotheses

1. Anaerobic fitness (anaerobic capacity and muscle power) , aerobic capacity, body
composition, upper body strength, lower body strength, peak heart rate following
stair climbing , and percentage of maximal heart rate achieved during stair climbing
will each be significantly correlated to CPAT performance. Anaerobic fitness and
muscular strength combined will be a significantly better predictor of CPAT
performance than any of the other individual factors alone.

2. Lower body strength, followed by aerobic capacity and body composition, will be
significantly related to the rate-pressure product achieved during a stair climbing task.

3. Differences in anaerobic fitness, aerobic capacity, body composition, upper body
strength, lower body strength, peak heart rate in response to stair climbing, and
percentage of maximal heart rate achieved during stair climbing will account for
successful completion of the CPAT, with measures of anaerobic fitness and strength
being of greater importance.

Significance

The results of this study will serve to better characterize the physiological
attributes that best determine firefighting performance as assessed by the CPAT. This
may be useful in combination with other studies for future development of optimal
training interventions for improving firefighting performance. This information may also
be helpful for developing more optimal, efficient, and fiscally prudent screening
processes.
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Methods


Subjects: Thirty-three volunteer and career firefighters, ages 18-45, from
Baltimore-Washington metropolitan area fire departments volunteered to participate in a
5 day testing battery. Subjects were actively recruited by the Maryland Fire and Rescue
Institute (MFRI) through the use of flyers, internet advertising on the MFRI website, and
in-person recruitment visits to local fire departments. After the methods and procedures
of the study were explained, all subjects signed a consent form approved by the
Institutional Review Board of the University of Maryland, College Park. All subjects had
no more than 2 risk factors for cardiovascular disease as determined by guidelines set
forth by the American College of Sports Medicine (2). A minimum of 1 day of rest
separated each day of testing in order to minimize fatigue.

Design/Variables: This research project utilized a cross-sectional design. The
study sought to determine the physiological characteristics which are correlated with and
predict firefighting performance. In this case, the various physiological characteristics
acted as independent variables, and include body composition (% body fat & fat free
mass), aerobic capacity, peak anaerobic power and mean anaerobic power, muscle power,
muscle endurance, and strength. Firefighting performance, as assessed by the CPAT, was
the dependent variable.
One-repetition maximum (1-RM) strength: Air-powered resistance training
machines (Keiser A-300 Leg Extension machine, Chest Press machine, Leg Press
machine, Keiser Sports/Health Equip. Co., Inc., Fresno, CA) were used to test 1-RM. 1-
RM strength testing has been shown to have a test-retest reliability of r = 0.98 (91) to
0.99 (45). The test measures the amount of force the exercised muscles can exert in a
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given movement pattern. The 1-RM is considered to be the reference standard for the
measurement of maximal strength by the American College of Sports Medicine (1).
The 1-RM strength testing was performed bilaterally on the chest and leg press,
and unilaterally on the knee extension exercise. For all strength tests, subjects were
familiarized to the testing equipment between 2 and 5 days prior in order to account for
the effects of motor learning (skill acquisition) on performance. The estimated 1-RM
was determined as a percentage of bodyweight. Chest press 1-RM was 75% of
bodyweight, knee extension was equal to bodyweight, and leg press was equal to 3 times
bodyweight. The familiarization consisted of 4 sets at varying percentages of the
estimated 1-RM. The first set was performed for 10 repetitions with no resistance and the
second set was performed for 8 repetitions at 10% of estimated 1-RM. The third set was
performed for 5 repetitions at 30% of estimated 1-RM and 3 repetitions at 50% of the
estimated 1-RM were performed for the fourth set.
For all strength tests, subjects completed 2 minutes of seated cycling as a warm-
up. Testing proceeded with single repetition sets and 1 minute rest between each set.
After each trial they provided a number on the Pain/Discomfort and Rating of Perceived
Exertion scales. The resistance increased in a manner that allowed for the determination
of 1-RM within 8 to 10 trials.
For the leg press, the subjects were seated on the machine with the seat positioned
so that the knee joint forms a 90 degree angle. They were instructed to place their arms
across their chest and to breathe normally. A successful repetition was counted when the
knee was fully extended. For the chest press, subjects were seated in a position that
aligned the handlebars with the xyphoid process. Subjects were instructed to keep the
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head and back against the back pad and their feet flat on the floor. A successful
repetition was achieved when the elbows were fully extended. For the knee extension
exercise, each leg was tested separately, with the right leg tested first. The seat was
positioned so that the axis of rotation of the knee joint lined up with the axis of rotation of
the knee extension machine. Subjects were instructed to cross their hands across their
chest and breathe normally. A restraint was placed across the subject’s lap in order to
restrict movement of the hips. A successful repetition was achieved when the knee joint
angle exceeded 165 degrees, as assessed by an indicator light when this angle was
reached.
Muscle Endurance: The Keiser A-300 Chest Press machine and Leg Press
machine were used to test muscle endurance. A maximal repetition test against a pre-
determined percentage of strength was used to determine muscular endurance, as
endorsed by American College of Sports Medicine as a valid measure of muscular
endurance (1). The test measures fatigue resistance with a reliability index of greater
than r = 0.97 in a previous study (56).
Muscle endurance in the chest press and leg press exercises were assessed directly
after the achievement of a 1-RM in the respective movement. A 5 minute rest period was
taken after the final trial of the 1-RM testing process. The same seat position was used
for both 1-RM and muscle endurance testing. Subjects completed as many repetitions as
possible with 80% and 70% of the 1-RM in the leg press and chest press, respectively.
The same criteria were used to determine a successful repetition as during 1-RM testing,
with the addition that the subject must completely return to the starting position at the
conclusion of each repetition. They were instructed to breathe normally, ensure a full
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range of motion, and to move continuously. Pausing between repetitions resulted in the
termination of the test. The total number of repetitions was recorded.

Muscle Power: An air-powered resistance training machine (Keiser A-300 Leg
Extension machine, Keiser Sports/Health Equip. Co., Inc., Fresno, CA) was used to test
for muscle power. Additionally, a computer program (A430 version 1.6.0.19 (2003),
Keiser Sports/Health Equip. Co., Inc., Fresno, CA) was used to measure muscle power in
watts. Subjects completed a 5 minute warm-up on a cycle ergometer prior to power
testing, which was performed on an air-powered knee extension resistance machine. The
Keiser machine measures maximal movement velocity and force production to calculate
muscle power in watts, using a specialized timing device and load cell. Muscle power
testing was shown to be both reliable and valid in a previous study using similar
equipment, with an intra-class correlation coefficient of 0.91 (13).
A single practice trial was performed at 30% of the previously established
unilateral 1-RM prior to muscle power testing at 50%, 60%, and 70% of the previously
determined 1-RM for each leg. Three sets of a single repetition were performed at each
resistance. For each trial, subjects were instructed to extend the knee as fast and as hard
as possible. For each set, the right leg was tested and immediately followed by the left
leg. A 1 minute rest period was taken between sets at the same percentage of 1-RM.
After all 3 sets were completed for a given percentage of 1-RM, a 2 minute rest was taken
prior to the next series of tests. Test results were recorded using a software program from
Keiser Sports/Health Equipment Co. Muscle power was tested on 2 separate occasions,
with approximately 3-5 days in between. The higher of the 2 values was used, as this
value would represent peak power.
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Peak Anaerobic Power, Mean Anaerobic Power, and Fatigue Index: A Wingate
Anaerobic Cycling Test (WAnT) was administered using a cycle ergometer (Monark
824E) to determine a fatigue index, maximal anaerobic power, and mean anaerobic
power. Reliability for peak anaerobic power and mean anaerobic power range from 0.95
to 0.98 (27, 44, 46). The validity of the WAnT is based upon correlations between
physiological measures and performance measures. Peak anaerobic power and mean
anaerobic power, as measured by WAnT, have been shown to be correlated with the
percentage of fast-twitch muscle fibers, as well as the total area of fast-twitch fibers (46).
Additionally, peak anaerobic power has been shown to be significantly related to a 50m
run (r = -0.91) (46).
Subjects pedaled with no resistance for 3 minutes, followed by a pair of 5-second
practice sprints separated by approximately 30 seconds of active recovery with no
resistance. Following the second practice sprint, they rested passively for 2 minutes
while remaining on the bike. After 2 minutes had elapsed, they pedaled slowly for 30
seconds, followed by pedaling as fast as possible for 30 seconds against a resistance
equivalent to 7.5% of bodyweight. The number of revolutions completed in each 5
second period was recorded over the course of the 30 second test. The test concludes
with 5 minutes of slow pedaling with no resistance.
Aerobic Capacity: A treadmill (Trackmaster), Douglas bags, and a mass
spectrometry unit (Perkin-Elmer) were used to determine maximal oxygen uptake
(VO2max). Subjects wore a mask that collects all gas expired through the mouth. The
nose was clipped to ensure that all air was exhaled through the mouth. A hose connected
the mask to a leak-proof bag where the gas was collected for standardized periods of
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