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Body armor effect on heat
- 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
- 2. “Learning to care for those in harms way”
- 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
- 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
- 21. Results
- 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)
- 23. 0 10 20 30 40 50 Mean Oxygen Consumption 16.8 18.8 34.8 40.8 VO 2 (ml*kg -1 *min -1 ) VO 2 SP NBA VO 2 SP BA VO 2 MP NBA VO 2 MP BA * ** P < 0.001 12% 17%
- 24. 0 2 4 6 8 10 Mean Blood Lactate 1.74 1.74 3.96 6.66 9.59 8.78 mmol/L BL NBA BL BA PT NBA PT BA PPPB NBA PPPB BA * NS NS * P < 0.001 68%
- 25. 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 16.6 BorgRPEScore * ** P < 0.001 16% 25%
- 26. 0 5 10 15 20 Hang Time NBA Hang Time BA Mean Hang Time 19.1 7.02 Seconds 63% * * P < 0.001
- 27. 0 2 4 6 8 10 Pull-Ups NBA Pull-Ups BA 9.12 3.59 NumberofRepititions Mean Number of Pull-Ups * P < 0.001 * 61%
- 28. 0 5 10 15 20 25 30 Step Test NBA Step Test BA Mean Step Count 28.7 24.3 StepCount * * P < 0.001 15%
- 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%
- 39. Logistic Regression Results – Slow Pace Variable Variance Explained Specificity Sensitivity Heart Rate 37-50% 80% 71%
- 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
- 41. 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%
- 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
- 43. Logistic Regression Results Physical Performance Battery Variable Variance Explained Specificity Sensitivity Pull-Ups 48-65% 89% 75%
- 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).
- 50. Recommendations Body Composition Standards Fitness Levels Entry Requirements – age now 42 (NPS) Caloric needs
- 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
- 52. Questions
Editor's Notes
- 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.