Impact of Body Armor on Physical Work Performance

Colonel Ric Ricciardi9 August 20069th Annual Force Health Protection ConferenceAlbuquerque, New Mexico rricciardi@usuhs.mil

“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