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Impact of Body Armor on Physical Work Performance
Colonel Ric Ricciardi9 August 20069th Annual Force Health Protection ConferenceAlbuquerque, New Mexico [email protected]
“Learning to care for those in harms way”
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
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
Title of Study
The Impact of Body Armor on Physical Work Performance
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
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).
January 7, 2006Pentagon Study Links Fatalities to Body Armor
MSNBC.comFebruary 2006
U-S Soldiers Question Use of More Armor
Study Goal
Identify Physiological Risks associated with personal protective equipment such as body armor
Develop Strategies to Prevent or Mitigate Risks
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
Central Hypothesis
Individuals who wear body armorwill have:
Increased Energy Expenditure Increased Physiological FatigueReduced Work Performance
Conceptual Model of the Impact of Physical Load on Physical Performance
PhysicalLoad:
Personal Protective Equipment
(Body Armor)
Energy Expenditure
Physiological Fatigue
Work Performance
Physiological Risk
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
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
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
Assessment of Physiologic Fatigue
Blood Lactate Borg Perceived Physical Exertion Scale Heart Rate
Assessment of Work Performance
Scores on Physical Performance Battery Heart Rate Oxygen Consumption
Other Variables
Body adiposity approximated by body mass index (BMI) defined as weight in kg/(height in meters)2
Anthropometric Measures Bioelectrical Impedance Analysis
Procedures Recruitment Informed Consent Counterbalance Testing: 2 sessions with & without body armor
Treadmill Walking Test Physical Performance Battery Blood Analysis
Results
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)
0
10
20
30
40
50
Mean Oxygen Consumption
16.818.8
34.8
40.8
VO
2 (ml *
kg-1
* m
in-1
)
VO2
SP NBA VO2 SP BA VO
2 MP NBA VO
2 MP BA
*
** P < 0.001
12%
17%
0
2
4
6
8
10
Mean Blood Lactate
1.74 1.74
3.96
6.66
9.59
8.78m
mol
/L
BL NBA BL BA PT NBA PT BA PPPB NBA PPPB BA
*
NS
NS* P < 0.001
68%
0
5
10
15
20
RPE SP NBA RPE SP BA RPE MP NBA RPE MP BA
Mean Rating of Perceived Physical Exertion
8.35
10.4
14.3
16.6B
org
RP
E S
core
*
** P < 0.001
16%
25%
0
5
10
15
20
Hang Time NBA Hang Time BA
Mean Hang Time
19.1
7.02
Sec
onds
63%*
* P < 0.001
0
2
4
6
8
10
Pull-Ups NBA Pull-Ups BA
9.12
3.59
Num
ber o
f Rep
ititio
ns
Mean Number of Pull-Ups
* P < 0.001*
61%
0
5
10
15
20
25
30
Step Test NBA Step Test BA
Mean Step Count
28.7
24.3
Ste
p C
ount
** P < 0.001
15%
0
50
100
150
200
HR SP NBA HR SP BA HR MP NBA HR MP BA
Mean Heart Rate
107118
164
180B
eats
per
min
ute
*
*
* P < 0.001
10%
10%
0
10
20
30
40
RR SP NBA RR SP BA RR MP NBA RR MP BA
Mean Respiratory Rate
25.227.7
33.9
40B
read
ths
per m
inut
e
* P < 0.001 18%
10%
*
*
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
1.07V
CO
2 / V
O2
Mean Respiratory Exchange Ratio
8.6%* P < 0.001*
NS
Aim 2Compare 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
Women (n = 17) Men (17)
NBA BA p PercentIncrease 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
Physiological and Perceptual Response Values by Gender at Medium Pace
Women (n = 17) Men (n = 17)
NBA BA p PercentIncrease 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
Women (n = 17) Men (n = 17)
NBA BA p PercentChange 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
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)
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
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%
Logistic Regression Results – Slow Pace
Variable Variance Explained Specificity Sensitivity
Heart Rate 37-50% 80% 71%
Mean Heart Rate – Slow Pace without Body Armor
Did not complete vs. completed testing
Did not Complete Testing
CompletedTesting P
Heart Rate (beats per
minute)118.0 ± 8.4 100.0 ± 13.5 <0.001
Logistic Regression Results – Moderate Pace
RPE = Rating of Perceived Physical Exertion
Variable Variance Explained Specificity Sensitivity
Heart Rate 37-50% 80% 71%
RPE 45-61% 90% 86%
Lactate 56-75% 90% 92%
Mean Heart Rate, RPE and Lactate at Moderate Pace without Body Armor
Did not complete vs. completed testingDid not
Complete Testing
CompletedTesting 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
Logistic Regression Results Physical Performance Battery
Variable Variance Explained Specificity Sensitivity
Pull-Ups 48-65% 89% 75%
Mean Pull-Ups without Body Armor Did not complete vs. completed testing
Did not Complete Testing
CompletedTesting P
Pull-Ups 4.3 ± 3.9 12.5 ± 4.4 <0.001
Conclusions
The results of this study demonstrate that wearing interceptor body armor under simulated work conditions significantly: Increases energy costReduces physical work performance
capabilities and Increases physiological fatigue
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
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)
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 NBAVO2 MP BA
VO
2 (m
l * k
g-1 *
min
-1)
Percent Body Fat
R = 0.50 p= 0.004R = 0.64 p< 0.001
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).
Recommendations
Body Composition Standards Fitness Levels Entry Requirements – age now 42 (NPS) Caloric needs
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
Questions