Physical Activity, Fitness and Injuries Among Women in the Army

Michelle Canham Chervak, PhD, MPHBruce H. Jones, MD, MPH

Bradley C. Nindl, PhD

21 May 2014 UNCLASSIFIED

U.S. Army Public Health Command

2 UNCLASSIFIED

Vision: World-Class Provider of Public Health Services across DA and DoD.

Mission: Promote health and prevent disease, injury, and disability of Soldiers and military retirees, their Families, and DA Civilian employees; assure effective execution of full spectrum veterinary service for Army and DoD Veterinary missions.

•Reasons for interest in training related injuries– Physical fitness is a requirement for the Army that needs

physical training/exercise– Injuries are a problem for the Army and most result from

physical training; women experience more injuries

•Risk factors for training-related injuries include:– Extrinsic Factors– Intrinsic Factors

•Conclusions

Overview of Factors for Injuries to Women in the Army

IMAGE SOURCE: http://www.defenseimagery.mil/ 120109-A-RX742-054UNCLASSIFIED2

Relative Burden of Injuries and Diseases, U.S. Army Active Duty, 2012

Other*

Infect/Parasite

Resp Disease

Digestive

Genitourinary

Skin

Sense Organ

Resp Infections

Musculoskeletal

Signs/Symptoms

Mental

Injury

Medical encounters

Individuals affected

Hospital bed days

Medical Encounters/Individuals Affected

ICD

-9-C

M C

od

e G

rou

ps

Data source: Defense Medical Surveillance System, 2013; Prepared by Army Institute of Public Health, Injury Prevention Program

UNCLASSIFIEDIncludes all ICD-9-CM code groups with less than 80,000 medical encountersDiagnosis group Injury contains both injury and musculoskeletal related injuries

3

Army OIF-OND/OEF Air Medical Evacuations by Diagnosis Group, 2003 - 20101-4

1 Total evacuations: n= 57,9682 ICD-9 codes obtained from TRAC2ES3 Percents represent the percent of all evacuations in each diagnosis group4 Operation Iraqi Freedom (OIF-OND) started on 19 March 2003, Operation Enduring Freedom (OEF) started in October 2001

Unknown

Other

Skin

Neoplasms

Infectious

Endocrine

Respiratory

Musculoskeletal

Circulatory

Nervous system

Genitourinary

Digestive

Ill-defined conditions

Mental health

Battle injury

Non-battle injury

Non-Battle injuries

Battle injuries

Disease

17.0%

9.5%

8.8%

5.9%

4.9%

3.5%

3.2%

2.1%

1.7%

1.6%

1.4%

1.4%

1.4%

3.6%

0.2%

33.8%

UNCLASSIFIED4

Annual Percent of Service Members withAny Injury or Exercise & Sports Activity (ESA)-Related

Injury by Military Service

N = 10,692

Service

Any Injury (>1) ESA Injury (>1)

Percent Injured

Percent Injured

Army 56.6 29.0

Navy 41.4 19.9

Marine Corps 53.0 32.6

Air Force 42.7 21.8

All Services 48.9 25.4

Source: Status of Forces Survey Analysis 2008, USAPHC Technical Report No. 12-HF-0PDT-08

UNCLASSIFIED5

Risks of Injury for Women Compared to Men

Length of Training (weeks)

Study Year data Collected Recruits (n) Cumulative Injury

Incidence (%) Risk Ratio

Women Men Women Men Women:Men

8 weeks

Kowal et al. 1978

1978 770 347 62 26.2 2.4

Bensel and Kirk 1983

1980 644 1,840 41.2 20.7 2.0

Jones et al. 1993

1984 186 124 50.5 27.4 1.8

Bell et al. 1993

1988 352 509 57 27 2.1

Jones et al. 1996

1996 84 159 65.5 41.5 1.6

Knapik et al. 2001

1998 305 604 58 30.8 1.9

9 weeks

Canham-Chervak et al. 2000

1998 498 655 65.3 30 2.2

Knapik et al. 2008

2007 915 2,147 64.7 36.9 1.8

Source: Knapik, J. et al. USAPHC Epidemiological Report #S.0007856-11, 2012UNCLASSIFIED8

N Number Injured Follow-Up

Injury Rate per 1000 Soldiers per

Month

Risk Ratio

(95% CI)

Women 453 198 6 months 73 1.16*

(1.0-1.3)

Men 5,029 1,909 6 months 63 1

Injury Rates for Women and Men after the Implementation of a Physical Training Program

in an Operational Army Unit

Source: EDS-IPP, AIPH, APG, MD

*p=0.02

N=5482

UNCLASSIFIED6

Casualty Type

Male Female

Cases (n)

Percent (%)

Incidence per 1,000

Cases (n)

Percent (%)

Incidence per 1,000

Battle Injury

8,721 19.4 6.2 179 2.7 1.1

Non-Battle Injury

15,990 35.6 11.5 1,542 23.7 9.8

Illness20,22

8 45.0 14.5 4,791 73.6 30.9

Total44,93

9 100.0 32.2 6,512 100.0 41.5

Distribution of Casualty Type by Gender for Air Evacuated Soldiers from CENTCOM , OIF/OEF (Army) 2001-2009

Incidence: cases per 1,000 deployed Soldiers

Data source: US Transportation Command Regulating and Command & Control Evacuation System (TRAC2ES)

9UNCLASSIFIED7

• Extrinsic– Training

• Amount• Type Activity

– Equipment– Environment

• Intrinsic– Gender– Age– Race– Physical Fitness

• Health Related• Skill Related

– Multivariate Models• Stratified Models• Logistic Regression

Risk Factors for Training Injuries

IMAGE SOURCE: http://www.defenseimagery.mil111101-A-VB845-030

UNCLASSIFIED9

Extrinsic Risk Factors

Physical Training and Activity

IMAGE SOURCE: Flickr / U.S. ArmyUNCLASSIFIED10

Injuries per Year among Menand Women by Miles Run per Week

Source: Koplan JP, Powell KE, Sikes RK. JAMA; 248:3118, 1982UNCLASSIFIED11

Lower Activity Moderate Activity Higher Activity0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

3.6

5.6

7.2

9.6

13.2

14.9

Men

Women

Activity Level (steps per day)

Inju

ry In

cid

en

ce

Ra

te (

ca

se

s/1

00

0 p

ers

on

da

ys

)

Injury Risks for Female and Male Trainees by Footsteps During BCT

Men n=1174Women n=898

Average # of footsteps per day: Lower=14,772 ± 400; Moderate=16,346 ± 768; Higher=17,948 ± 550

UNCLASSIFIED12

Distribution (%) of Injuries in Women and Men by Activity in Basic Combat Training

Other

Land Navigation

Unsure

Army Physical Fitness Test

Combatives

Barracks Activities

Confidence/Obstacle Courses

Road Marching

Physical Training

No Specific Activity (Gradual Onset)

0% 5% 10% 15% 20% 25% 30% 35% 40%

Women

Men

Percent (%) Injured

Ac

tiv

itie

s A

ss

oc

iate

d w

ith

Inju

ry

Source: Knapik J et al. Military Medicine 178(5):500-506, 2013Fort Leonard Wood, April 2011

Rank order by percent of women injured in each categoryMen n=4,128; Women n=2,907

UNCLASSIFIED13

Other

Repairing/maintaining equipment

Riding/driving on a motorized vehicle

Other Exercise

Stepping/Climbing

Sports

Lifting/moving heavy objects

Walking/Hiking/Marching

Running

0% 5% 10% 15% 20% 25% 30% 35% 40%

Men

Women

Percent (%) Injured

Ac

tiv

itie

s A

ss

oc

iate

d w

ith

Inju

ry

Rank order by percent of women injured in each categoryMen n=1,078; Women n=120

Distribution (%) of Injuries in Women and Men by Activity in an Operational Unit

UNCLASSIFIED14

Cause of Injury for Soldiers Air Evacuated from CENTCOM by Gender, OIF/OEF: 2001 – 2009a

Data source: US Transportation Command Regulating and Command & Control Evacuation System (TRAC2ES)

Falls

and

nea

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s

Sports

and

PT

Mot

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Crush

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a

Liftin

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ushin

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Wea

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relat

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ishap

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Wea

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BE, boo

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Cuttin

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Enviro

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Compli

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med

/sur

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Mac

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Air tra

nspo

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Heat,

fire

and

corro

sives

Toxic

sub

stan

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Other

spe

cified

age

nt0

5

10

15

20

25

30

Male

Female

Causes

Pe

rce

nt

Air

Ev

ac

ua

ted

fo

r N

BIs

N: men=10,792; women=947

UNCLASSIFIED15

–Gender

–Age

Intrinsic Risk Factors

IMAGE SOURCE (TOP): Flickr / U.S. Army, (BOTTOM): http://www.defenseimagery.mil/ 111002-A-QD683-210

UNCLASSIFIED16

Risks of Injury for Women Compared to MenLength of Training (weeks)

Study Year data Collected Recruits (n) Cumulative Injury

Incidence (%) Risk Ratio

Women Men Women Men Women:Men

8 weeks

Kowal et al. 1978

1978 770 347 62 26.2 2.4

Bensel and Kisk 1983

1980 644 1,840 41.2 20.7 2.0

Jones et al. 1993

1984 186 124 50.5 27.4 1.8

Bell et al. 1993

1988 352 509 57 27 2.1

Jones et al. 1996

1996 84 159 65.5 41.5 1.6

Knapik et al. 2001

1998 305 604 58 30.8 1.9

9 weeks

Canham-Chervak et al. 2000

1998 498 655 65.3 30 2.2

Knapik et al. 2008

2007 915 2,147 64.7 36.9 1.8

Source: Knapik, J. et al. USAPHC Epidemiological Report #S.0007856-11, 2012UNCLASSIFIED18

N Number Injured Follow-Up

Injury Rate per 1000 Soldiers per

Month

Risk Ratio

(95% CI)

Women 453 198 6 months 73 1.16*

(1.0-1.3)

Men 5,029 1,909 6 months 63 1

Injury Rates for Women and Men after the Implementation of a Physical Training Program

in an Operational Army Unit

Source: EDS-IPP, AIPH, APG, MD

*p=0.02

N=5482

UNCLASSIFIED6

Relative Risk of Injury for Women and Men by Age in Basic Combat Training

17.0-19.9 y 20.0-24.9 y 25.0-29.9 y ≥30 y0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1

1.1

1.4 1.4

1 1

1.3

1.5

Men

Women

Age (years)

Ha

zard

Ra

tio

fo

r In

jury

Source: Knapik, J et al. JSCR 23(3):685-697, 2009.Men n=2124Women n=902

UNCLASSIFIED19

Intrinsic Physical Fitness Risk Factors

Health-related fitness

Skill-related Fitness

Cardiorespiratory endurance

Muscular endurance

Muscular strength

Body composition

Flexibility

Agility

Balance

Coordination

Speed

Power

Reaction time

UNCLASSIFIED20

IMAGE SOURCE: http://www.defenseimagery.mil/ 090818-A-AO884-339

UNCLASSIFIED21

Injury Risks by Quartiles of Run Time for Female and Male Trainees

Fast Q1 Q2 Q3 Q4 Slow0

10

20

30

40

50

60

70

14

10

26

42

3633

57

61

Men

Women

Quartiles of Run Time

Inju

ry in

cid

en

ce

(%

)

N = 310 (186 women, 124 men) Source: Jones B et al Am J Sports Med, 1993

UNCLASSIFIED22

916 19

2432

40 44

65

01020304050607080

1st(fastest)

2nd 3rd 4th(slowest)

Run Quartiles

LE

Overu

se I

nju

ry I

ncid

en

ce

(%) Males

Females

Association of Initial Run Time and LE Overuse Injury* BCT

RR Males: Q4/Q1 =2.81 p=<0.001; RR Females: Q4/Q1=2.03, p=<0.001

* Any LE overuse injury in the first 9 weeks of training IET, Ft Leonard Wood, 2002

UNCLASSIFIED23

IMAGE SOURCE: http://www.defenseimagery.mil/ 110403-A-VF572-002

UNCLASSIFIED24

Injury Risks by Push-Up Repetitions for Female and Male Trainees by Quartiles

Knapik, USACHPPM Epicon Report No 29-HE-8370-99, 1999

Q1(few) Q2 Q3 Q4(many)0

10

20

30

40

50

60

70

3033

24 21

60 5955

43

Men

Women

Quartiles of Push-ups

Inju

ry I

nc

ide

nc

e (

%)

N=692 Men, 398 Women; Risk Ratio (Q1/Q4): Men=1.4, Women=1.4p-value for Trend: Men = 0.02, Women = 0.01 (Ft Jackson, 1998)

UNCLASSIFIED25

≤55 55-66 67-75 ≥760%

10%

20%

30%

40%

50%

60%

Men

Repetitions

Pe

rce

nt

Inju

red

≤30 31-40 41-47 ≥480%

10%

20%

30%

40%

50%

60%

70%

Women

Repetitions

Pe

rce

nt

Inju

red

Injury Risks by Push-Up Quartiles for Women and Men in an Operational Unit

Men n=2,530Chi Square for Trend: p=<0.01

Women n=219Chi Square for Trend: p=0.08

UNCLASSIFIED26

Injury Risks for Female and Male Trainees by Quintiles of Body Mass Index (BMI)

Low Q1 Q2 Q3 Q4 Q5 High0

5

10

15

20

25

30

35

40

45

50

23.325.6

20.923.2

24.8

43.641.3

38

30.7

37.4

Men

Women

BMI by Quintile

Inju

ry In

cid

en

ce

(%

)

Source: Jones BH. Body Composition & Physical Performance. National Academy Press, pp 141-173, 1992.Ft. Jackson, 1988; Men n = 1053 Women n= 895, 8 weeks of training

UNCLASSIFIED27

Women

Run Q1 (Fastest)

Run Q2 Run Q3 Run Q4 Run Q5(Slowest)

Overall

BMI Q1 (lowest)

29.2 38.9 45.3 49.3 63.1 41.9

BMI Q2 26 35.8 40.2 47.7 56 39.1

BMI Q3 24.6 33.9 38.3 46.6 55.4 39.5

BMI Q4 26.1 33.4 36.5 40.8 56 39.6

BMI Q5 (highest)

25 30.7 36.5 40.8 54 41.2

Overall 26.5 35 39.3 44.6 56

Percent of Female Soldiers Injured by Run Time and BMI Quintile

Source: DMSS, 2014. Prepared by Army Institute of Public Health, Injury Prevention Program

N= 41,727 Trend of increased injury risk with decreased fitness. Significance: Run Q1, BMI Q3 << Run Q5, BMI Q1, RR=3.5; p < 0.001

UNCLASSIFIED28

Incidence (%) of Women and Men in Army BCT with One or More Injury (2010 to 2012)

Source: AIPH Analysis 2013

GenderIncidence/Risk of

Injury Risk Ratio W/M (95% CI)

Women 39.7 % 2.00 (2.00 - 2.10)

Men 19.4% 1.00

N = 182,638 (155,670 men, 26,968 women)

UNCLASSIFIED29

Quintile (Run Time)

Men Women

N % Injured N % Injured

(Fast) ≤14.3 36,444 14.2 526 33.5

14.4-15.4 35,255 16.8 981 30.1

15.5-16.5 34,458 19.1 2,121 28.7

16.6-18.3 30,366 22 6,258 33

(Slow) ≥18.3 19,147 30.3 17,082 44.2

Total 155,670 19.4 26,968 39.7

Injury Risk for Women and Men in Basic Combat Training Stratified by Run Time

RR (Unadjusted) 2.0 (2.0-2.1)

RR (Adjusted for Fitness) 1.5 (1.4-1.5)

Source: USAPHC injury analysis 2010-2012UNCLASSIFIED30

Risks of Injury for Women Compared to Men

Length of Training (weeks)

Study Year data Collected Recruits (n) Cumulative Injury

Incidence (%) Risk Ratio

Women Men Women Men Women:Men

8 weeks

Kowal et al. 1978

1978 770 347 62 26.2 2.4

Bensel and Kisk 1983

1980 644 1,840 41.2 20.7 2.0

Jones et al. 1993

1984 186 124 50.5 27.4 1.8

Bell et al. 1993

1988 352 509 57 27 2.1

Jones et al. 1996

1996 84 159 65.5 41.5 1.6

Knapik et al. 2001

1998 305 604 58 30.8 1.9

9 weeks

Canham-Chervak et al. 2000

1998 498 655 65.3 30 2.2

Knapik et al. 2008

2007 915 2,147 64.7 36.9 1.8

Source: Knapik, J. et al. USAPHC Epidemiological Report #S.0007856-11, 2012UNCLASSIFIED31

Women Men

Age 20 20

Height (cm) 162 175.1

Weight (kg) 57.8 76.3

Body Fat (%) 26.6 16.4Initial 1-mile run

(min) 10.1 7.6

Initial Sit-Ups (n) 30.9 43.7

Initial Push-Ups (n) 10.9 32.4

Injury Risk Ratio = 2.1 (1.78-2.5)

Body Composition and Physical Fitness of Female and Male Army Basic Trainees

Source: Bell NS, et al. Am J Prev Med. 18(3S):141-6, 2000.

Men n=509, Women n=352

UNCLASSIFIED32

Gender & Risk of ≥ 1 Training-Related Injury, Controlling for Fitness, Age & Race

  Risk Factor OR* 95% CI

GenderMen –– ––

Women 1.14 (0.48-2.72)

Run time

Very Fast –– ––Fast 1.47 (0.68-3.18)

Average 1.54 (0.91-2.62)Slow 2.52 (1.26-5.04)

Very Slow 3.23 (1.59-6.58)

Strength

Very Strong –– ––Strong 1.41 (0.80-2.50)

Average 1.61 (0.90-2.88)Weak 2.1 (0.88-5.04)

Very Weak 2.11 (0.83-5.36)

Age (yrs)

< 20 –– ––20-24 1.5 (1.00-2.23)

25 + 1.26 (0.69-2.31)*Multivariate logistic regression; other variables include SU, PU, Race

Source: Bell NS, et al. Am J Prev Med. 18(3S):141-6, 2000.

N= 861; 509 men, 352 women

UNCLASSIFIED33

• Crude injury risk is greater for women than for men.

• Injury risk increases with increased activity

• Activities associated with injury risk are similar for men

and women (physical-training related)

• Injury risk is highest at the lowest fitness levels for women

and men.

Conclusions Regarding Fitness and Injuries Among Women in the Army

UNCLASSIFIED34

• There are some women in every level of fitness.

• On average, women’s fitness levels are lower than men’s.

• When corrected for fitness, women’s injury risks are similar to men’s

• Women with highest BMIs at each fitness level at lower risk of injury.

• Higher BMI or % body fat not as important as fitness for injury risk

• All conclusions need more research with focus on operational units.

Conclusions Regarding Fitness and Injuries Among Women in the Army

UNCLASSIFIED34