1. Impact of Body Armor
on Physical Work
Performance
Colonel Ric Ricciardi
9 August 2006
9th Annual Force Health Protection Conference
Albuquerque, New Mexico
rricciardi@usuhs.mil
3. Co-Investigators
Laura Talbot, Ph.D, Ed.D., RN
Associate Professor, GSN, USUHS
Patricia Deuster, Ph.D., M.P.H.
Professor, Military and Emergency Medicine,
USUHS
4. Special Thanks
US Army Nurse Corps
Study Participants from USN, USAF, USA and USPHS
TriService Nursing Research Program
Honorable Daniel K. Inouye
The Henry M. Jackson Foundation for the Advancement of
Military Medicine
5. Title of Study
The Impact of Body Armor on Physical Work
Performance
6. Background
Personal Protective Equipment (such as body
armor) when worn in high threat military
environments impacts military personnel’s work
performance
Decrements in Physical Performance impacts
both mission and the individual
However little is known about the physiological
effects of wearing body armor
7. Body Armor - Military Relevance
Reduces Lethality
Saves Lives
Prevents Injury
References: Hoge, C. W., et al.(2004); Patel, T. H., et al., (2004);
Mabry, R. L., et al., (2000).
8. January 7, 2006
Pentagon Study Links Fatalities to Body Armor
MSNBC.com
February 2006
U-S Soldiers Question Use of More Armor
9.
10. Study Goal
Identify Physiological Risks associated
with personal protective equipment such
as body armor
Develop Strategies to Prevent or Mitigate
Risks
11. Specific Aims
Determine changes in work performance, energy cost,
and physiological fatigue as a function of body armor as
compared to no body armor.
Compare how body armor alters energy cost and
physiological fatigue under conditions of low and
moderate physical activity levels.
Estimate how body composition and background
variables such as age and sex affect:
work performance
energy cost
physiological fatigue
12. Central Hypothesis
Individuals who wear body armor
will have:
Increased Energy Expenditure
Increased Physiological Fatigue
Reduced Work Performance
13. Conceptual Model of the Impact of Physical
Load on Physical Performance
Physical
Load:
Personal
Protective
Equipment
(Body Armor)
Energy Expenditure
Physiological Fatigue
Work Performance
Physiological
Risk
14. Overview of Study Design
Counterbalance
16 Participants tested without
body armor in first session
16 Participants tested with
body armor in first session
Same 16 Participants tested with
body armor in second session
Same 16 Participants tested
without body armor in second
session
32 Participants
15. Population
Healthy military personnel aged 18-40
Free of heart, endocrine and liver disease;
hypertension; and asthma by history and
physical exam
Nonpregnant
Able to perform treadmill exercise test
Able to wear body armor
16. Assessment of Energy Cost
Modified treadmill exercise using submax
protocol at 4.5 and 9 MET’s.
Peak oxygen consumption (VO2peak) defined by
highest 2 minute average, expressed in
mL/kg/min
17. Assessment of Physiologic Fatigue
Blood Lactate
Borg Perceived Physical Exertion Scale
Heart Rate
18. Assessment of Work Performance
Scores on Physical Performance Battery
Heart Rate
Oxygen Consumption
19. Other Variables
Body adiposity approximated by body
mass index (BMI) defined as weight in kg/
(height in meters)2
Anthropometric Measures
Bioelectrical Impedance Analysis
20. Procedures
Recruitment
Informed Consent
Counterbalance
Testing: 2 sessions with & without body armor
Treadmill Walking Test
Physical Performance Battery
Blood Analysis
22. Aim 1
Determine changes in work performance, energy
cost, and physiologic fatigue.
Statistics
A paired-samples t-test was conducted to
determine mean differences between the
variables under two conditions (wearing and
not wearing body armor).
Alpha level p<0.0025 (Bonferonni correction)
29. 0
50
100
150
200
HR SP NBA HR SP BA HR MP NBA HR MP BA
Mean Heart Rate
107
118
164
180
Beatsperminute
*
*
* P < 0.001
10%
10%
30. 0
10
20
30
40
RR SP NBA RR SP BA RR MP NBA RR MP BA
Mean Respiratory Rate
25.2
27.7
33.9
40
Breadthsperminute
* P < 0.001 18%
10%
*
*
31. 0
0.2
0.4
0.6
0.8
1
1.2
RER SP NBA RER SP BA RER MP NBA RER MP BA
0.873 0.894
0.985
1.07
VCO
2
/VO
2
Mean Respiratory Exchange Ratio
8.6%* P < 0.001
*
NS
32. Aim 2
Compare how body armor alters energy cost physiologic
fatigue under conditions of low and moderate physical
activity levels and whether that effect is the same in men
and in women.
Statistics
A one-way analysis of variance was conducted to
determine mean differences between women and men
under two conditions (wearing and not wearing body
armor).
Alpha level p<0.05
33. Women (n = 17) Men (17)
NBA BA p
Percent
Increase
NBA BA p
Percent
Increase
VO2
(mL∙kg-1
∙min-1
) 16.8 ± 1.4 18.9 ± 1.3 <0.001 12.5 16.8 ± 1.7 18.6 ± 2.0 <0.001 10.7
HR (beats/min) 109.1 ± 15.4 121.8 ± 17.0 <0.001 11.6
105.7 ±
14.0
114.9 ± 13.5 <0.001 8.7
R (VCO2
/VO2
) 0.87 ± 0.1 0.88 ± 0.06 0.76 1.1
0.87 ±
0.05
0.91 ± 0.06 0.02 4.6
RR (breaths/min) 26.3 ± 4.8 29.7 ± 5.6 <0.001 12.9 24.0 ± 3.6 25.8 ± 3.4 <0.001 7.5
RPE 8.7 ± 0.1 11.0 ± 1.9 <0.001 26.4 8.7 ± 0.05 9.9 ± 1.4 <0.001 13.8
Physiological and Perceptual Response Values by Gender at Slow Pace
34. Physiological and Perceptual Response Values by Gender at Medium Pace
Women (n = 17) Men (n = 17)
NBA BA p
Percent
Increase
NBA BA p
Percent
Increase
VO2
(mL∙kg-1
∙min-1
) 33.6 ± 2.2 38.9 ± 3.3 <0.001 15.7
35.90 ±
4.8
42.6 ± 5.7 <0.001 18.6
HR (beats/min) 164.5 ± 14.9 179.0 ± 12.4 <0.001 8.8
162.5 ±
17.7
180 ± 14.5 <0.001 10.7
R (VCO2
/VO2
) 0.97 ± 0.1 1.06 ± 0.14 <0.001 9.2 1.00 ± 0.1 1.06 ± 0.14 0.002 6.0
RR (breaths/min) 34.7 ± 5.5 40.9 ± 6.2 <0.001 17.9 33.2 ± 6.4 39.1 ± 7.1 <0.001 17.8
RPE 14.1 ± 2.2 16.8 ± 2.3 <0.001 19.1 14.4 ± 2.4 16.5 ± 2.0 <0.001 14.6
35. Women (n = 17) Men (n = 17)
NBA BA p
Percent
Change
NBA BA p
Percent
Change
Baseline 1.5 ± 0.7 1.5 ± 0.7 0.7 NC 1.9 ± 0.9 2.0 ± 0.6 0.8 NC
Post Treadmill 3.5 ± 2.4 6.0 ± 2.8 <0.001 71.4 4.4 ± 2.4 7.3 ± 2.4 <0.001 65.9
Post PPB 7.2 ± 2.7 7.5 ± 3.4 0.4 NC
11.9 ±
4.0
9.9 ± 3.1 0.01 16.9
Blood Lactate Levels by Gender
36. Aim 3
Estimate how body composition and background
variables affect energy cost, physiological
fatigue, and work performance.
To consider predictors of treadmill completion
while wearing body armor, multivariate analyses
using a logistic regression model were
conducted on predictor variables (percent body
fat, age, sex, rating of perceived physical
exertion, and heart rate)
37. Logistic Regression Results
Predictors of Test Completion
Physical Characteristics
Age, Waist Circumference, Percent Body Fat and BMI
Slow Pace
Heart Rate
Moderate Pace
Blood Lactate, RPE and Heart Rate
Physical Performance Battery
Pull-Ups
38. Logistic Regression Results – Body Fat
*Body fat cut points = 17% in men and 26% in women
Variable
Variance
Explained
Specificity Sensitivity
Body Fat* 20-26% 79% 67%
40. Mean Heart Rate – Slow Pace without Body
Armor
Did not complete vs. completed testing
Did not
Complete
Testing
Completed
Testing
P
Heart Rate
(beats per
minute)
118.0 ± 8.4 100.0 ± 13.5 <0.001
42. Mean Heart Rate, RPE and Lactate at
Moderate Pace without Body Armor
Did not complete vs. completed testing
Did not
Complete
Testing
Completed
Testing
P
Heart Rate 173.57 ± 10.9 156.5 ± 15.6 0.001
RPE 16.1 ± 1.8 13.0 ± 1.5 <0.001
Lactate 6.1 ± 2.3 2.5 ± 0.9 <0.001
RPE = Rating of Perceived Physical Exertion
44. Mean Pull-Ups without Body Armor
Did not complete vs. completed testing
Did not
Complete
Testing
Completed
Testing
P
Pull-Ups 4.3 ± 3.9 12.5 ± 4.4 <0.001
45. Conclusions
The results of this study demonstrate that
wearing interceptor body armor under
simulated work conditions significantly:
Increases energy cost
Reduces physical work performance
capabilities and
Increases physiological fatigue
46. Conclusions
Of note, these physiologic changes
occurred from a mean increase in body
mass of only 15.7% (17.7% women and
14.1% men)
Nonlinear increases in VO2
Effect size 0.60 at the slow pace and 0.75
at the medium pace on VO2
47. Conclusions
The physical characteristic variable that
was the best predictor of test completion
in subjects wearing body armor was
percent body fat.
Lower body fat is associated with:
↑ VO2peak
↓ heart rate
↑ pull-ups
↓ rating of perceived physical exertion
↓ Blood lactate levels (men)
48. Relationship between VO2 and Percent Body Fat at Medium Pace
25
30
35
40
45
50
55
5 10 15 20 25 30 35 40 45
VO2 MP NBA
VO2 MP BA
VO
2
(ml*kg
-1
*min
-1
)
Percent Body Fat
R = 0.50 p= 0.004
R = 0.64 p< 0.001
49. Conclusions
The variable most predictive of treadmill
test completion was blood lactate.
In field testing where blood analysis may
not be available, the best predictor of test
completion is heart rate at the slow (4.5
METs) or moderate pace (9 METs).
51. Future Research
Thermoregulation
Field Studies
Specific to Military Related Occupational
Specialties
Female Model of Body Armor – Related to
chest pain complaints
Warrior Personal Protective System Model
Balanced Personal Protective System
As we prepare to “learn to care for those in harms way” it is only fitting that we begin this presentation taking a moment to remember those who are the fabric as we weave knowledge to improve upon the federal health care system….our beloved warriors from all services, and those that support them.
I would like especially thank my advisors for their support, mentoring, and patience over the past 3 years, and for their commitment to support me in the future.
I have many to thank, but in the nature of time I will begin with:
In a high threat military environment, body armor and other load-bearing personal protective equipment are widely used by military personnel for protection against fragmentation, handgun, and rifle projectile injuries. To date, no studies have examined the metabolic cost and the subsequent consequences of wearing body armor. It is hypothesized that over time, the wearing of body armor increases physical exertion and metabolic cost, thus increasing physiological fatigue, and reducing work performance.
The interceptor body armor is an effective and highly valued piece of gear by soldiers and marines in the global war on terrorism and has saved many lives (Hodge, et al., 2004; Patel, et al., 2004).
There are many anecdotal reports from soldiers in the field whose body armor was hit by bullets and fragments where minor or no injury occurred (Mabry, et. al., 2000).
Hodge in the NEJM
Patel in the Journal of Trauma
Mabry in the Journal of Trauma
Hoge, C. W., Castro, C. A., Messer, S. C., McGurk, D., Cotting, D. I., & Koffman, R. L.(2004). Combat duty in Iraq and Afghanistan, mental health problems, and barriers to care. New England Journal of Medicine,35(1), 13-22.
Patel, T. H., Wenner, K. A., Price, S. A., Weber, M. A., Leveridge, A., & McAtee, S.J. (2004) A U.S. Army forward surgical team&apos;s experience in operation Iraqi freedom. Journal of Trauma, 57(2), 201-207.
Mabry, R. L., et al., (2000). United States army rangers in Somalia: An analysis of combat casualties on an urban battlefield. The Journal of Trauma, 49, 515-529.
Recently, there have been numerous reports by the news media on the importance of body armor – and its impact on saving lives. In addition, soldiers and marines have commented on the need to have a “balanced approach” to personal protective equipment…how much is too much?
The overall goal of this project is to identify the physiological risks for military personnel associated with personal protective equipment such as body armor, and to develop strategies to prevent or mitigate any negative effect.
SPECIFIC AIMS OF DISSERTATION are to:
Determine changes in work performance, energy cost, and physiological fatigue as a function of body armor as compared to no body armor.
Compare how body armor alters energy cost and physiological fatigue under conditions of low and moderate physical activity levels.
Estimate how body composition and background variables such as age and sex affect:
work performance
energy cost
physiological fatigue
The central hypothesis is that individuals who wear body armor will have increased energy expenditure, increased physiological fatigue, and reduced work performance when performing physical activity as compared to times when they are not wearing body armor.
This study was a within-subjects repeated measure design: participants were tested with and without body armor under all conditions. Participants reported to the Human Performance Lab (HPL) at the Uniformed Services University of the Health Sciences for two sessions. Each session was a minimum of five days apart and lasted approximately one and a half - two hours. The independent variable (wearing of body armor) was counterbalanced to control for time and order. Half of the participants were tested wearing body armor first; the other half were tested without wearing body armor first.
Criteria for inclusion are: 1) 18-40 years of age; 2) able to speak and read English; 3) willing and able to exercise and climb stairs with a load of 20 lbs; 3) willing to receive venipuncture, and 4) members of the armed services.
Criteria for exclusion are: 1) hypertension 2) use of glucose lowering medications; 3) pregnancy; 4) endocrine diseases; 5) cardiac disease; 6) liver disease; 7) asthma; and 8) use of beta blockers.
4.5 METs = Women 2.3 and men 2.4mph at 5% grade
9 METs = Women 3.6 and men 3.8mph at 10% grade
Blood Lactate was measured three times – baseline, post treadmill testing and after the physical performance battery
Rating of perceived physical exertion was measured twice – after slow pace and after moderate pace on the treadmill
Heart Rate was measure continuously throughout testing using polar system
Scores on physical performance battery:
Pull-Ups – measured with palms facing chin bar and counted each time chin was elevated over the bar.
Hang-Time – measured in seconds with arms in flexed position and chin over bar
Oxygen consumption (VO2peak) measured by indirect &gt;&gt;&gt;&gt;&gt;&gt; with real time recording
Anthropometric Measures: Waist Circumference Waist Hip Ratio
including height, weight, waist and hip circumference, WHR, body mass index, blood pressure, pulse, and bioelectrical impedance analysis
Bioelectrical Impedance Analysis: Quantum II, RJL Systems
After obtaining informed consent and being cleared for participation, anthropometric measures will be obtained. All measurements and testing will be done in the HPL at USUHS.
Determine changes in work performance, energy cost, and physiological fatigue as a function of body armor as compared to no body armor.
Statistical analyses were performed using SPSS version 12.0.1 for Windows (SPSS, Inc., Chicago, IL). Values are reported as means ± standard deviation in the tables and figures. Statistical assumptions of normality, linearity and multicollinearity were tested using scatterplots and plots of standardized residuals. To evaluate the effects of wearing body armor on energy cost and physiological fatigue (VO2, blood lactate, heart rate, respiratory exchange ratio, respiratory rate, and rating of perceived physical exertion) and physical work performance, a paired t-test with Bonferonni correction was used to determine mean differences between the variables under two conditions (wearing and not wearing body armor). Statistical significance was set at P&lt; 0.0025 using a Bonferonni correction. Logistic regression was used to predict treadmill completion wearing body armor and the studied variables of percent body fat, age, heart rate and rating of perceived physical exertion) .
Mean VO2 at slow pace (SP) and medium pace (MP) in participants not wearing (NBA) and wearing (BA).
* Value significantly different (P &lt; 0.001) between NBA and BA at SP and MP.
Mean serum lactate at baseline (BL), post treadmill testing (PT) and post physical performance battery (PPPB). * Value significantly different (P &lt; 0.001) between PT NBA and PT BA.
Mean Rating of Perceived Exertion (RPE) at slow pace (SP) and medium pace (MP) in participants not wearing (NBA) and wearing (BA). * Value significantly different between NBA and BA at SP and MP (P &lt; 0.001).
Mean number of pull-ups in participants not wearing body armor (NBA) and wearing body armor (BA).
* Value significantly different (P &lt; 0.001).
Compare how body armor alters energy cost, and physiological fatigue under conditions of low ( 4.5 METs) and moderate (9 METs) physical activity levels.
BMI split at 25: variance 13-18% specificity = 71% sensitivity = 70%
Waist cut at 102cm in men and 89cm in women: not significant
It should be noted, however, that this metabolic impact occurred from as little as a 15.7% mean increase in body weight from wearing the body armor. Additionally of note, as work intensity increased, changes in oxygen consumption were not linear, with mean increases in VO2 while wearing the Interceptor Body Armor being 12% at slow pace and 17% at medium pace.
These results are clinically important since during military, police and homeland security operations, personnel are required to routinely walk long distances and perform moderate intensity critical occupational tasks while wearing body armor.
Exercise and increased levels of fitness have been associated with lower heart rate during exercise and strenuous activities in numerous studies [15-18]. The lower heart rate in physically fit individuals is a result of increased stroke volume and myocardial contractility and a decreased sensitivity to catecholamines. Prevention measures such as aerobic and strength physical training to keep an individuals heart rate below 100 at a sustained normal walking pace (4.5 METs) and below 157 at a moderate walking pace (9.5 METs) may be the best method to prevent or mitigate physical work performance decrements from wearing body armor.
In conclusion, this study indicates that wearing body armor imposes a significant impact on human physiology and performance. Specifically, wearing Interceptor Body Armor significantly increases VO2 while walking at both slow and moderate paces. Walking at a slow pace increased energy needs by 42 Kcal/hour whereas walking at a moderate or military maneuver-like pace increased energy needs by 126 Kcal/hour. Total blood lactate levels were 68% higher while wearing body armor (6.7 ± 2.6 vs. 4.0 ± 2.4 mmol/L), which indicates the onset of muscle fatigue and physical activity limitations. Interceptor Body Armor significantly impacted physical work capacity of militarily relevant tasks. In summary, the potential for physical exhaustion is high and the performance of physical tasks is markedly impaired when wearing body armor for sustained work operations. It is likely that these findings will generalize to military deployment related physical duties, but further studies in the field would be required.